LOFAR Family Meeting 2025

22 Sept 2025, 09:00 → 26 Sept 2025, 13:05 Europe/Paris

Institut de Physique du Globe de Paris

The 2025 LOFAR Family Meeting will take place in Paris, France, from 22–26 September 2025. It will be hosted at the IPGP (Paris Institute of Planetary Physics), located in the heart of the Latin Quarter, near the Jardin des Plantes.

The meeting will feature a mix of exciting talks on the latest scientific results, updates on the LOFAR2.0 upgrade, and other recent developments within the LOFAR community.

The conference fee is 400€, which includes lunches, coffee breaks and conference dinner. A limited number of travel supports are available for early-career researchers. If you wish to apply, please contact lfm2025.contact@obspm.fr with a short motivation statement, preferably before the abstract submission deadline.

Monday 22 September

09:00 Welcome

Science talks

1 Recent Advances in the LOFAR-EoR and NenuFAR Cosmic Dawn Projects

Direct observation of the Cosmic Dawn and Epoch of Reionization via the redshifted 21-cm line will have unprecedented implications on the study of structure formation in the early Universe. This exciting goal is challenged by the difficulty of extracting the feeble 21-cm signal buried under bright astrophysical foregrounds and contaminated by numerous systematics. The LOFAR-EoR and NenuFAR Cosmic Dawn projects aim to statistically detect the 21-cm signal fluctuations from the EoR and Cosmic Dawn, and to pave the way for the SKA EoR/CD experiment, which will be capable of directly imaging the large-scale neutral hydrogen structures from these distant epochs.

In this talk, I will present the latest results from the LOFAR-EoR and NenuFAR Cosmic Dawn collaborations. The LOFAR-EoR team recently published a new and deeper upper limit on the 21-cm signal power spectrum, now extending across a broader redshift range, further tightening constraints on the thermal and ionisation history of the intergalactic medium during the EoR. On the Cosmic Dawn front, the NenuFAR team is preparing the release of a new upper limit around z∼20, which for the first time allows constraints on non-standard models predicting an excess in the diffuse radio background.

These new results will be discussed, along with the advances in calibration and foreground mitigation that enabled them. I will also address their broader implications for the upcoming SKA-Low CD/EoR observations.

Speaker: Florent Mertens (Paris Observatory (LUX))

2 Overdispersed radio source counts and excess radio dipole detection

The source count dipole from wide-area radio continuum surveys allows us to test the cosmological standard model.
Many physical radio sources are observed as multiple components, which can cause an overdispersion of the source counts distribution.
We account for this effect via a new Bayesian estimator, based on the negative binomial distribution.
Combining the two best understood wide-area surveys, NVSS and RACS-low, and the deepest wide-area survey, LoTSS-DR2, we find that the source count dipole exceeds its expected value as the kinematic dipole amplitude from standard cosmology by a factor of $3.67 \pm 0.49$ --- a $5.4\sigma$ discrepancy.

Speaker: Lukas Böhme (Bielefeld University)

3 WEAVE-LOFAR: Harnessing the Power of Low-Frequency Radio Observations Using Optical Spectroscopy

The faint radio-source population includes sources dominated both by star formation and active galactic nuclei (AGN), encoding the evolution of activity in the Universe. Investigating its nature requires accurately identifying the dominant source of emission in each system - a task that spectroscopy is uniquely well-suited to address. To demonstrate this, we make use of available spectra provided by the Dark Energy Spectroscopic Instrument (DESI) to probabilistically classify 5,173 z~1 radio sources from the LoTSS Deep Fields.This was done by combining three tools: (i) the identification of a radio excess, (ii) the BPT diagram, and (iii) a modified Mass Excitation diagram, alongside Monte Carlo methods to estimate the probability that each source is either a star-forming galaxy (SFG), a radio-quiet AGN (RQ AGN), or a high-\slash low-excitation radio galaxy (HERG or LERG). This approach extends the probabilistic classification framework of previous works by nearly doubling the redshift range, such that we can now probabilistically classify sources over the latter half of cosmic history. Using a 90 per cent reliability threshold, we find reasonable overall agreement (~77 per cent) with state-of-the-art photometric classifications, but significant differences remain, including that we identify 2-5 times more RQ AGN. Furthermore, our high-confidence spectroscopic classifications show that radiatively-efficient and inefficient AGN exhibit clearly distinct Eddington-scaled accretion rate distributions, contrary to recent findings in the literature. Overall, our results highlight the need for new and forthcoming spectroscopic campaigns targeting radio sources, on the pathway to the SKA. In particular, with the launch of the WEAVE-LOFAR survey, we will obtain over a million spectra of sources identified in the LOFAR surveys. This dramatic increase in sample size will allow us to probe the interplay between star formation and AGN activity, as well as the different accretion modes, thereby providing us with a deeper and more complete understanding of the low-frequency radio population.

Speaker: Marina Arnaudova (The University of Edinburgh)

4 Radio-Detected Lyα Emitters at $1.88 < z < 3.52$: AGN Fraction and Lyα Visibility

Lyα emitters (LAEs), characterized by their prominent Lyα emission at 1216 Å, are key tracers of high-redshift galaxies and play a crucial role in our understanding of galaxy evolution and cosmic reionization. In particular, radio-detected LAEs offer valuable insights into the interplay between star formation, active galactic nuclei (AGN) activity, and the interstellar medium.

Using the HETDEX–LOFAR spectroscopic catalog, which combines spectroscopic redshifts from HETDEX DR4 with radio data from LOFAR DR1, we identify 400 robust Lyα+radio sources in the redshift range $1.88 < z < 3.52$, selected from a parent sample of 79,022 LAEs and 28,705 radio sources. After correcting for completeness, we find a radio-detected AGN fraction of $1.67 \pm 0.33%$ among LAEs and a Lyα-emitting fraction of $23.76 \pm 4.76%$ among radio sources. Both fractions increase with Lyα and radio luminosity.

We observe weak correlations between luminosity, redshift, and Lyα line width. A small subset of resolved radio galaxies, with projected radio sizes ranging from 141 to 502 kpc, highlights the diversity of Lyα environments.

Our results confirm that the majority of LAEs are star-forming and radio-quiet, while a luminous minority host AGN. The presence of Lyα emission in some radio AGN suggests ongoing interaction with cold gas, indicating a complex interplay between AGN feedback, gas dynamics, and galaxy evolution at high redshift.

Speaker: Sai Zhai (Leiden University)

10:45 Coffee / tea break

Science talks

5 The role of galaxy properties and environmental factors on radio AGN prevalence

In this talk we explore the intricate role of both galaxy-intrinsic and environmental factors in triggering radio AGN activity in the local Universe. We investigate the prevalence of radio AGN by combining radio observations from the LOFAR Two-Metre Sky Survey (LoTSS) data release 2 with optical data from the extensively characterised Sloan Digital Sky Survey (SDSS). The large samples allow us to break degeneracies between stellar mass, black hole mass, bulge mass, morphology, and environmental parameters, including both local and global galaxy density. Consistent with previous studies, our findings confirm that stellar mass is a primary driver of radio AGN prevalence. However, at fixed stellar masses, galaxy morphology plays only a small role, with the fraction of galaxies hosting a radio AGN being up to two times higher in elliptical galaxies than in spirals of the same mass. But environmental factors emerge as significant determinants for radio-AGN activity, even after controlling for the dependence on stellar mass. Specifically, global density has a stronger correlation with the percentage of galaxies with radio-AGN activity than local densities or tidal interactions. These results support a cooling-flow scenario in which AGN activity depends primarily on the thermodynamic properties of the available gas. Our work provides new insights into the demographic and environmental drivers of AGN activity and contributes to a more complete understanding of the complex mechanisms of gas inflows towards supermassive black holes that have emerged as essential for understanding AGN triggering and maintenance.

Speaker: Lara Alegre (University of Hertfordshire)

6 Studies of compact AGNs at low frequencies with LOFAR

There are still many open questions and uncertainties regarding the evolution of radio galaxies. Compact AGNs, such as Gigahertz Peaked Spectrum (GPS) and Compact Steep Spectrum (CSS) sources, are thought to be the precursors of classical double-lobed radio galaxies. However, some studies suggest their evolution may be more complex than previously assumed. These sources can be temporarily frustrated by their host environments or even be short-lived and transient. Low-frequency radio observations provide a unique opportunity to probe the oldest plasma and investigate the early stages of activity and dynamics in young AGNs.

In this study, we present the results of an analysis of a sample of CSS sources that remain unresolved in the FIRST and LoTSS surveys. Using the LOFAR-VLBI pipeline, we resolved their structures into components at 150 MHz and compared them with higher-frequency observations from MERLIN and the VLA. In several cases, we detected 150 MHz emission from lobes that are not visible at higher frequencies. We modelled the synchrotron spectra of these components to investigate absorption processes and estimate source ages. Furthermore, we report significant asymmetries in the brightness of radio lobes in some sources and discuss potential physical explanations for this phenomenon in light of our new observations.

Speaker: Aleksandra Krauze (Nicolaus Copernicus University)

7 Sub-arcsecond wide-field imaging with the LOFAR LBA

Very-long baseline interferometry (VLBI) across a wide field of view is notoriously difficult given the extreme data volume and compute resource requirements. Nevertheless, improvements in the calibration and imaging algorithms in the past few years made it possible to carry out wide-field imaging at sub-arcsecond resolution using the LOFAR High-Band Antenna (HBA).
The strong variations of the ionosphere across the LOFAR international baselines of up to $2000\,$km require us to carry out direction-dependent calibration of the ionospheric systematic effects. There are by now several fields across which a full direction-dependent calibration of LOFAR HBA including the international stations was achieved.

For the LOFAR Low-Band Antenna (LBA), operating at ultra-low frequencies of ~50 MHz, calibrating the international baselines is even more challenging given the increased severity of the ionospheric systematic effects and the lower signal-to-noise ratio compared to the HBA. Previously, calibration of the international baselines was only shown to be feasible in a direction-independent manner and only for a small number of exceptionally bright (${>}10\,$Jy) and compact sources. If calibration of sources with flux densities ${\leq}1\,$Jy is possible was unknown.

In this talk, I will present the first ever wide-field VLBI image obtained with the LOFAR LBA system, reaching sub-arcsecond resolution ($0.9''\times0.5''$) across 6$\,$deg$^2$. In $8\,$h of observation time of the field around the galaxy cluster Abell 2255, a noise level of $650\,\mathrm{µJy\,beam^{-1}}$ in the frequency range 42-66$\,$MHz was obtained. The ionospheric effects were calibrated using ten different direction-dependent calibrators. This breakthrough shows that, at least under mild ionospheric conditions and in presence of a 2-3 Jy compact infield-calibrator, wide-field VLBI at ultra-low frequencies is possible.

In addition to the calibration strategy, I will discuss the image quality and properties and showcase the scientific value of the data using high-resolution spectral index maps of the radio galaxies in the Abell 2255 cluster.

Lastly, I will outline important considerations for long-baseline imaging in the LBA as standard observation mode for LOFAR 2.0, also in context of NenuFAR as LOFAR Super-Station in the interferometer.

Speaker: Dr Henrik Edler (ASTRON)

8 A view of radio relics at sub-arcsecond resolution with LOFAR

Radio relics are elongated diffuse sources located in the outskirts of merging galaxy clusters, tracing merger-induced shocks. In the last decade, high-resolution observations - up to a fraction of an arcsecond - at GHz frequencies have revealed that they are characterized by filamentary structures, challenging our understanding of these sources.
In this talk, I will present the first images of radio relics as seen by the International LOFAR Telescope (ILT). These novel observations, together with their high-frequency counterparts, are essential to define the exact place of particle acceleration which is crucial for theoretical models.

Speaker: Gabriella Di Gennaro (INAF-IRA)

9 Searching for revived fossil plasma sources in galaxy clusters

LOFAR surveys have enabled unprecedentedly detailed analysis of large-scale, diffuse, and steep-spectrum sources in galaxy clusters, such as radio relics and halos. These are thought to arise from particle re-acceleration operated in the intra-cluster medium (ICM) by shocks and turbulence triggered by a cluster merger. Similar processes are likely also responsible for the re-ignition of fossil electrons from radio galaxies, thus forming amorphous and filamentary sources known as radio phoenices. These are interesting sources to investigate the injection of seed relativistic particles into the ICM, the re-energising mechanisms, and the merging history of the host cluster. However, the ultra-steep spectrum ($\alpha \gtrsim 1.5-2$) of phoenices makes them to be remarkably elusive, and the lack of sensitive and high-resolution multi-wavelength data at low radio frequencies, which are essential for a proper classification, has hampered their study.
LOFAR offers a unique opportunity to investigate phoenices. I will present the analysis of a sample of 7 candidate phoenices, which have been selected by visual inspection of a sample of low-mass and nearby galaxy clusters in LoTSS-DR2, and then followed-up with the uGMRT. I will show radio images, optical/X-ray overlays, and spatially-resolved spectral index maps at 144-400 MHz that we used to confirm the classification of our targets. Our sample highlights the challenges of selection and classification of these sources. I will present the first attempt to derive constraints on the statistical properties of phoenices, by exploring similar correlation to those known for radio relics and halos.

Speaker: Luca Bruno (Istituto Nazionale di Astrofisica (INAF))

10 New Scaling Relations of Galaxy Cluster Radio Halos

The Universe hierarchical formation process can be investigated through the fundamental relations of galaxy cluster observables. Since the matter accretion is gravity-dominated, the hot plasma within galaxy clusters displays a self-similar behaviour, following precise scaling relations that link spatially resolved quantities to global ones. Similarly, the diffuse, non-thermal cluster component (radio halo) is tightly connected to the system properties, with its total radio halo power showing a strong correlation with the system's mass ($P_R - M$ relation). However, only integrated quantities have been systematically investigated for this component, leaving the non-thermal emission on sub-cluster scales largely unexplored.
In my talk, I address this gap by exploiting the wide and deep radio survey conducted by LOFAR (the LoTSS), which allows for the detection of a large number of radio halos with sufficient angular resolution to characterise in detail their emission.
To this aim, I consider a well selected sample of clusters observed by the LoTSS, also leveraging deep XMM-Newton data from the CHEX-MATE project. I use these data to derive novel scaling relations that link global and spatially resolved radio halo emission with the cluster properties.
Using an analytical model to describe the halo radial profiles, I obtain several key results. I demonstrate how the various features displayed by the halo surface brightness profiles are recovered by properly accounting for the cluster mass and redshift. Furthermore, this analysis provides an assessment of the role of cluster dynamics in shaping the non-thermal emission. By comparing model predictions and observed scaling relations, it also yields constraints on the impact of different radio halo properties, such as the halo average emissivity and the halo size.
Finally, I adopt a physically motivated model to improve the conventional treatment of the observed $P_R-M$ relation. By explicitly incorporating the magnetic field contribution, this methodology provides, for the first time, a statistical estimate of the average cluster magnetic field. Remarkably, thanks to the novel approach adopted, I can derive a scaling relation between the cluster magnetic field and its mass, with results that align consistently with independent literature estimates.

Speaker: Marco Balboni (DIFA UNIBO - IASF Milan)

13:00 Lunch break

Science talks

11 Unveiling the Spectral Properties of Radio Halos in the Galaxy Clusters of the LOFAR sky survey

Radio halos are large-scale, diffuse radio sources with low surface brightness located in the central regions of galaxy clusters, extending across several megaparsec scales. They are believed to originate from cosmic rays re-accelerated by merger-induced turbulence by second-order Fermi mechanism. The turbulent re-acceleration model anticipates a substantial population of radio halos with very-steep spectra ($\alpha > 1.5$, where $S_\nu \propto \nu^{-\alpha}$) and a correlation between the turbulent energy, linked to the cluster merger event, and the resulting radio synchrotron spectral shape. But this hypothesis has not been tested extensively due to the absence of low-frequency sensitive radio observations. In this talk, I will present preliminary results on a project aimed to address for the first time in a complete sample the statistical spectral properties of radio halos by combining LOFAR and uGMRT data. The project focuses on a complete sample of 45 radio halos in the Second Data Release of the LOFAR Two-meter Sky Survey (LoTSS-DR2, 150 MHz), which was recently followed up at uGMRT 650 MHz. I will show the first results based on a subsample of 18 radio halos discussing the connection between their spectral properties and the dynamical state of the hosting clusters. Finally I will show how radio halo properties are connected with cluster mass and redshift and discuss implications of my results for the turbulent re-acceleration scenario for the formation of giant radio halos and highlight the importance of this study for future LOFAR observations.

Speaker: Koushika Sri Lakshmi srikanth (IRA-INAF Bologna)

12 Magnetic fields inside and beyond galaxy clusters with LOFAR

Magnetic fields are ubiquitous, permeating all large-scale cosmic structures — voids, filaments and galaxy clusters — and their strength decreases with thermal electron density. Understanding magnetic fields in the transition regions between clusters and filaments is crucial for unravelling the interplay of thermal and non-thermal processes and the mechanisms that amplify weak seed fields. While high-frequency observations probe μG-level fields in dense cluster cores, low-frequency instruments such as LOFAR excel at revealing much fainter fields in cluster outskirts, inter-cluster bridges and the cosmic web. In this talk, I will review the latest results obtained with LOFAR in this context, with a focus on supercluster environments, and discuss the advances anticipated with the advent of LOFAR2.0. Finally, I will highlight synergies with other polarisation surveys —most notably the Polarisation Sky Survey of the Universe’s Magnetism (POSSUM)— and outline how these efforts will set the stage for transformative science with the SKA.

Speaker: Chiara Stuardi (IRA INAF)

13 Galactic fields in the LoTSS

By the end of LOFAR 1.0 operations in the summer of 2024, the LOFAR Two-meter Sky Survey (LoTSS) had surveyed 85% of the Northern sky. The majority of the missing 15% of regions are at Galactic latitudes b<|20| degrees. However, a substantial fraction of the Milky Way was observed as part of the LoTSS, and will be part of data release three (DR-3), including two long contiguous segments between Galactic longitudes l=30-77 and l =123-180 degrees, as well as smaller regions around l=97-106, and l=190-209 degrees. We refer to these regions as the LoTSS Galactic Fields.

In this talk, I will present these fields and discuss their scientific potential for Galactic science. I will then showcase one science case in depth: that of Galactic supernova remnants (SNRs). I will show that these LoTSS data have the potential of altering our understanding of the low-energy electrons in SNRs as their low-frequency spectra deviate from classical power-law behavior. Moreover, they can address the “missing SNRs problem” with the discovery of tens of new sources in the survey regions.

Speaker: Maria Arias (Leiden Observatory)

14 Magnetic fields in planetary nebulae revealed by LOFAR

Planetary nebulae are gaseous shells ejected by low-mass stars at the end of their lives. The shells are ionized by hot central stars. The ionized plasma is a source of thermal radio continuum emission at GHZ frequencies with a spectral index between 0 and 2. This emission is spatially correlated with optical emission lines. LOFAR images revealed radio emission originating in many cases from regions different from optical emission. Radio spectra derived using archival data reveals the non-thermal spectral indices. This indicates presence of magnetic fields in planetary nebulae. We will discuss the possible origin of magnetic fields in these objects.

Speaker: Marcin Hajduk (University of Warmia and Mazury in Olsztyn)

15 ApPolLo- Apertif counterparts of polarised LOFAR sources

Polarisation studies over a significant redshift range are an important tool for understanding the evolution of cosmic magnetic fields and unrevealing their origin. As most depolarisation effects are highly wavelength dependent, the combination of different surveys allows us to distinguish between different effects.

We use the synergy of LOFAR and Apertif; starting with sources known to show significant polarised emission at 144 MHz, we image their 1.4 GHz counterparts and construct a catalogue of 598 polarised sources.
The comparison of polarisation properties, such as the fractional polarisation and the Rotation Measure values, at 1.4 GHz and 144 MHz provides us with information about the local environment of the sources as well as about the magnetic fields along the line of sight.
Combined with redshift information, we use this to study the evolution of the direct source environment and also to obtain a first redshift-dependent estimate of the Rotation Measure dispersion in cosmic web filaments.
We find a small fraction of sources to be more polarised at 144 MHz than at 1.4 GHz and two sources that don’t show significant polarisation in the Apertif data at all. We also present further investigation of those sources.

Speaker: Anna Berger (Bielefeld University)

Poster flash talks

16 The LBA view of bright radio galaxies and their science with long baselines

Over the past five years, LOFAR’s Low Band Antenna (LBA) system has opened a new observational window in the electromagnetic spectrum, enabling imaging at unprecedented resolution and sensitivity. Until now the Dutch array has mainly been used for science. We present results from observations using both the Dutch and full International LOFAR Telescope where we imaged bright 3C sources at arcsecond resolution. This marks the first time such imaging has been achieved under sub-optimal ionospheric conditions. With these normal and high-resolution, ultra-low-frequency maps, we investigate The AGN lobe kinematics and energetics, and test the validity of classical plasma aging models at low frequencies. These results lay the groundwork for more extensive long-baseline LBA observations in the near future, especially as LOFAR2.0 comes online

Speaker: Jort Boxelaar (INAF - IRA)

17 Evolution of large-scale magnetism through radio observations

Diffuse radio emission in galaxy clusters has been established to be linked with the presence of (re-)accelerated particles (i.e. cosmic rays, CRs) and magnetic fields (B). In the last years, thanks to the advent of highly-sensitive radio telescopes such as LOFAR and MeerKAT, the detection of diffuse radio emission has become possible also in clusters at high redshift (z>0.6). This allowed a first investigation of evolution of magnetic fields in the largest virtualised structures in the Universe, at the time of their formation. However, a complete statistical analysis is still missing. I will present the current knowledge on the cosmic evolution of magnetic fields, and the future window that SKA and its precursors will open. These new observations will provide crucial insights on the properties of the non-thermal component in the high-z cluster population.

Speaker: Gabriella Di Gennaro (INAF-IRA)

18 Tracking AGN Recurrent Activity: A Spectral Ageing Study of Giant DDRGs

Understanding how often, and for how long, radio-loud AGN switch their jets on and off remains a central problem in extragalactic astrophysics. Double-double radio galaxies (DDRGs), whose two distinct pairs of lobes preserve the imprint of successive jet episodes, are rare laboratories for tackling this issue, particularly when the systems reach giant ( >1 Mpc) dimensions, giving exceptionally clean separation between activity cycles. Until now, however, the lack of deep, well-matched imaging across the full radio band has limited quantitative age-dating of the plasma in such sources.

We present the first systematic spectral-ageing study of 14 giant DDRGs drawn from the LOFAR Two-Metre Sky Survey (LoTSS). Each source is now covered by six high-fidelity datasets spanning 54 MHz to 11 GHz: LOFAR LBA (LoLSS, 54 MHz), LOFAR HBA (LoTSS, 144 MHz), uGMRT Band 4 (550-750 MHz), and JVLA L, S, C, and X bands. In this presentation, I will showcase the new six-band images, which recover the full diffuse emission for nearly every target and unveil previously unseen features in greater detail. I will discuss how the morphological variety across the 14-source sample, ranging from edge-brightened inner doubles to hotspot-free relic lobes, encapsulates a continuum of restarted phases, and how the derived age distributions refine our picture of jet intermittency, particle acceleration and feedback on megaparsec scales. The LBA–HBA combination, along with uGMRT Band 4, secures precise injection indices. When coupled with the uGMRT–VLA data, we achieve robust curvature constraints, essential for diagnosing radiative losses, adiabatic expansion, and in-situ re-acceleration.

Such morphological diversity is echoed in the spectral properties. Low-frequency index maps from the LBA-HBA pair show injection spectra as flat as α ≈ 0.6 in several fresh hotspots, while outer relic lobes without hotspots steepen beyond α ≈ 1.2 between 54 MHz and 1.4 GHz, signalling severe radiative ageing. Fitting JP, KP and Tribble models with BRATS yields spectral ages ranging from a few Myr for the newly ignited inner jets to as much as ~80 Myr for the oldest outer cocoons. Combining these epochs gives duty-cycle estimates of 40% to 60%, implying that even the most powerful radio galaxies may spend comparable periods in active and quiescent states.

We place the giant DDRGs in their broader cosmic context by analysing both their surrounding environment and the megaparsec environments that host them. By comparing sources embedded in dense groups with those in more isolated regions, we explore how environmental pressure and fuel supply regulate jet shutdown, quiescence and re-ignition, shedding new light on the conditions that favour recurrent radio activity.

This study represents a major step forward in decoding AGN duty cycles, jet dynamics and particle acceleration mechanisms, refining our understanding of AGN feedback in large-scale structure formation.
Overall, these results demonstrate how LOFAR’s low-frequency leverage, coupled with uGMRT and JVLA coverage, can pin down both morphology and energetics of restarted AGN on megaparsec scales. They lay the groundwork for much larger duty-cycle studies with forthcoming LoTSS-DR3 and LOFAR 2.0 surveys, and ultimately for assessing the long-term impact of intermittent jets on galaxy and large-scale-structure evolution.

Speaker: Mousumi Mahato (Tartu Observatory, University of Tartu, Estonia)

19 Probing the environments of FRI and FRII radio galaxies in LoTSS DR2 with galaxy clusters

Aims. The origin of the morphological dichotomy between Fanaroff–Riley Class I (FRI) and Class II (FRII) radio galaxies has long
been debated, and some theories propose that it may be influenced by their environments. In this study, we use galaxy clusters as
tracers of environment to investigate whether environmental conditions play a significant role in shaping the FRI/FRII classification.
Methods. Using the LoTSS DR2 FRI/FRII catalogue, we construct two samples: a volume-limited sample and a paired sample, where
each FRII is matched to the nearest FRI in luminosity and redshift. We investigate the environmental properties of FRIs and FRIIs by
cross-matching them with a galaxy cluster catalogue, which identifies clusters based on the overdensity of stellar mass in the DESI
Legacy Imaging Surveys.
Results. We find that FRIs are more frequently located in galaxy clusters than FRIIs, particularly at high radio luminosities where
the cluster association of FRIIs drops significantly. However, once inside clusters, the two populations exhibit similar environmental
properties. In particular, the richness and M500 values of host clusters are comparable, and both FRI and FRII sources show nearly
identical radial density profiles, peaking at 0.5 × R500 and declining beyond R500. Furthermore, the likelihood of a radio galaxy being
the brightest cluster galaxy (BCG) is similarly high for both classes, with no significant differences in the properties of FRI-BCGs
and FRII-BCGs or their host clusters.
Conclusions. Our findings support a scenario in which the large-scale environments of FRIs and FRIIs are broadly similar once they
reside in clusters. The observed morphological dichotomy is unlikely to be driven solely by galaxy cluster properties, and may instead
reflect host-scale processes.

Speaker: Tong Pan (Leiden Observatory)

20 A broadband (150 MHz–8 GHz) study of giant radio galaxies larger than 2 Mpc

Giant radio galaxies (GRGs; size > 0.7 Mpc) are characterised by their exceptionally large sizes, with the largest reaching up to 7 Mpc. Recent low‑frequency sky surveys have boosted the known GRG population to 11.5k via machine learning–based searches. However, despite these growing statistical samples, detailed multifrequency studies—particularly of the largest GRGs (>2 Mpc, which is only ~6% of the population)—remain scarce. GRGs exceeding 2 Mpc are exceptionally rare, with surface densities of 0.2/deg² and comoving number densities as low as 1.5/(100 Mpc)³ across different radio surveys. These findings emphasise their significance as key targets for probing RG evolution.

To address this, we have selected a sample of the largest and brightest GRGs, all exceeding 2 Mpc. Notably, all GRGs in our sample exhibit high axial ratios like inner lobes of double-double lobed radio galaxies. Using our multi-frequency high-resolution deep radio maps, we have also explored low-frequency hotspot features. We discovered complex hotspot features with conical hotspots on both sides in 6 GRGs. All GRGs were meticulously observed with LOFAR, uGMRT, and VLA over a frequency range from 150 MHz to 8 GHz—with matched sensitivity and spatial resolution—to enable detailed spectral and dynamical age modelling using Synage, BRATS, and Dynage packages.

In this oral presentation, I will discuss the importance of studying 2-Mpc GRGs and present our comprehensive work, encompassing the acquisition of multifrequency data, its subsequent analysis, and the integration of these insights into the nature of these largest GRGs.

Speaker: Sagar Sethi (Astronomical Observatory of the Jagiellonian University)

21 ViCTORIA project: exploring galaxy evolution and magnetic fields in the Virgo Cluster with LOFAR and MeerKAT

The ViCTORIA (Virgo Cluster multi-Telescope Observations in Radio of Interacting galaxies and AGN) project is a unique multi-frequency radio survey of the Virgo cluster, combining LOFAR-LBA, LOFAR-HBA, and MeerKAT data to achieve unprecedented depth, resolution, and spectral coverage. The Virgo cluster, the closest rich cluster in the Universe, is a key target for understanding galaxy evolution, AGN feedback, and the role of the environment in shaping galaxy properties.

While two components of the ViCTORIA survey are conducted with LOFAR in the LBA (42–66 MHz) and HBA (120–168 MHz) bands, this talk will focus on the high-frequency MeerKAT L-band (856–1712 MHz) observations. This dataset offers a full-polarisation, wide-band coverage over 112 $\mathrm{deg}^2$, with a total number of pointings of 320. With a sensitivity of 7$\mu \mathrm{Jy beam}^{-1}$ at the nominal resolution of 7.6\text{$^{\prime\prime}$}, and complemented by a dedicated peeling strategy to mitigate the dynamic range limitations introduced by Virgo A (M87), the MeerKAT Virgo Cluster Survey enables high-fidelity imaging of diffuse and compact radio sources, including hundreds of cluster galaxies and low-surface-brightness features such as ram-pressure stripped tails and intra-cluster filaments.

This contribution will present the initial scientific results from the MeerKAT Virgo Cluster survey, which aims to derive polarised images, including RM synthesis of cluster galaxies and AGN, spectral index mapping between HBA and MeerKAT frequencies, and perspectives for combining all three frequency regimes to probe spectral curvature. By bridging the LOFAR and MeerKAT regimes, ViCTORIA enables resolved studies of magnetic fields, galaxy evolution processes, and environmental interactions spanning the frequency range from 42 to 1712 MHz and covering out to $r_{200}$, showcasing a synergistic approach with high legacy value for the LOFAR community.

Speaker: Alessandro Benati (INAF - IRA)

22 Interpreting the 21-cm signal with accurate simulations : impact of Bayesian inference methods and modelling uncertainty

The Square Kilometre Array is expected to measure the 21-cm signal from the Epoch of Reionization (EoR) in the coming decade, and currently operating radio-interferometers might provide a detection even earlier. Recently reported upper limits, including the latest LOFAR results, have already started constraining the astrophysical parameters of the models of the EoR. The challenges that lie ahead are twofold : correctly interpreting the observed data requires accurate Bayesian inference methods as well as realistic simulated models.
Using Loreli II, a database of hydro-radiative Licorice simulations of the EoR and the 21-cm signal, we show the impact of using several inference methods and discuss the commonly-used Gaussian likelihood approximation. On mock power spectra affected by thermal noise that corresponds to 100h of observations with the SKA, we report average differences between inference methods significantly smaller than the width of the posterior. Conversely, the impact of choices and approximations in the different 21-cm simulation codes used by the EoR community remains poorly understood. We discuss this aspect in light of the SKA Data Challenge 3b, as well as show the preliminary results of a comparison between 3D and 1D radiative transfer algorithms used respectively in Licorice and a version of the Beorn code modified to use the Licorice source model and applied to the Loreli II simulations. We discuss the impact of this modelling uncertainty on inference and on the interpretation of current upper limits.

Speaker: Romain Meriot (Imperial College)

23 Probing clusters outskirts: what can megahalos tell us?

Recent LOFAR observations of massive galaxy clusters revealed the presence of very extended and low brightness radio emission, named megahalo. Due to their size, megahalos could allow us to probe cluster volumes roughly 30 times larger than those covered by radio halos, opening a new window to study non-thermal components (cosmic rays and magnetic fields) and acceleration mechanisms in the peripheries of clusters. So far, megahalos have been observed by LOFAR in four massive clusters ($M>6\times10^{14} M_\odot$), although their existence still has to be confirmed with observations at other frequencies. In this talk, I will present three new candidate megahalos, including spectral index studies obtained combining data at 50 and 144 MHz. Furthermore, I will discuss the modelling of the brightness profiles of megahalos to improve our understanding on the acceleration mechanisms that might originate these sources. Finally, I will cover the analysis of LOFAR simulated observations aimed at determine the possible presence of systematic errors in the current megahalos detections.

Speaker: Matteo Cianfaglione (INAF - IRA - University of Bologna)

24 Tracing the growth and evolution of double-lobed radio quasars to z~4.2 with a large sample

The morphologies of extended, double-lobed radio quasars beyond z>2.5 remain largely uncharted, and no systematic census of their structural properties across cosmic time has yet been undertaken. Filling this gap is essential for understanding how powerful jets couple to their evolving environments from the early Universe to the present day. Understanding how powerful FR II radio quasars evolve from the local to the very high–redshift Universe requires large, deep radio-optical data sets that can both detect faint bridge emission and resolve the compact core–jet–hotspot structure of each source. No single large-sky radio survey delivers the necessary combination of sensitivity and resolution. Hence, we employ multiple complementary radio surveys to carry out this study. LoTSS provides the necessary sensitivity to trace low-surface brightness bridges, VLASS resolves compact cores and hotspots, and FIRST/NVSS deliver robust total fluxes. By combining these with spectroscopic quasar catalogues (e.g. SDSS), we have built the largest, wide-area sample of extended radio quasars spanning 0.13 < z < 4.2.

Starting from ∼7000 candidates, we inspected each source across the three surveys and used a Python package we developed to measure total angular size (and estimated total projected size), arm-length ratio (ALR) and misalignment angle (MA). After excluding core-dominated objects via VLASS/FIRST core flux densities and NVSS for total flux densities, 1569 FR II quasars remain. NVSS recovers the total flux in all but seven cases, giving reliable core-dominance factors; LoTSS-DR2 data were essential for identifying every object above z = 2.5, owing to its superior sensitivity to low-surface-brightness emission. The final catalogue covers projected sizes from 33 to 989 kpc and includes 35 extended quasars at z > 3, with the most distant at z = 4.2 (190 kpc). This is the largest RQ above z>4. Our newly identified 35 extended FR II quasars at z>3 are the largest high-redshift set yet assembled, which span projected sizes of 45–792 kpc (median ≈ 254 kpc) and include three “giants’’ (> 700 kpc), the most distant giant radio sources known. Their ≥100 kpc lobes imply sustained jet activity in substantial gaseous haloes, making each source a compelling signpost of a forming massive structure; together they provide a uniquely powerful tracer ensemble for proto-cluster searches at the dawn of cosmic time.

Our analysis shows that when the sample is split into contiguous redshift bins, we find a modest but significant increase in both ALR and MA, and a decrease in projected size with redshift, implying that high-z quasars are systematically more distorted. Intriguingly, those trends disappear when sources are instead binned by projected size. MA and ALR rise steeply as doubles grow from ∼30 kpc to ∼300 kpc, then flatten in >300 kpc sources, implying that larger lobes are intrinsically straighter and more balanced.
Nearly 80 % of the catalogue lies in the forthcoming LoTSS-DR3 footprint; combining DR3 fluxes with NVSS will allow us to examine the spectral properties of these sources and help us to understand ICCMB-induced fading of bridge emission out to z ≈ 4.

The 1569-object sample - by far the largest set of extended radio quasars with measured morphology in this redshift range, opens a path to calibrate the evolution of core-to-lobe ratios, test jet–jet-environment interactions across cosmic time. Our new measurement tool already streamlines the geometrical analysis and will be vital for inspecting large new samples. Beyond the immediate science, the catalogue supplies a unique set of labelled images for training convolutional networks to identify FR II morphology automatically. This will be crucial for harvesting the millions of RLQs as well as radio galaxies expected from LoTSS-DR3, LoTSS-Deep, SKA pathfinders, and ultimately with the SKA.

Speaker: Dr Pratik Dabhade (Astrophysics Division, NCBJ, Warsaw, Poland)

25 Role of environment in the jet powering mechanism in radio quasars - insights from the LOFAR Two-metre Sky Survey (LoTSS)

A key component of AGN feedback is the injection of kinetic energy from radio jets. However, there’s a fundamental lack of understanding of why quasars, otherwise very similar, have such a wide range of radio jet powers and, therefore, the impact of AGN jets. Using large samples from LoTSS DR2 coupled with a Bayesian parametric model, we can separate and quantify the jet and host galaxy contributions to quasar radio emission. We demonstrate that the traditional radio-loud/quiet quasar classification fails to reflect the physical origin of radio emissions. Instead, our model allows for redefining radio AGN populations based on physical processes, which enables robust measurement of quasar jet power evolution with environmental factors on large and small scales. We discovered a positive correlation between the jet fraction in quasar radio emission and their clustering amplitudes, suggesting a coevolution between jet production and halo mass, where most powerful jets are produced in the most massive haloes. Quasars dominated by jet activities reside in haloes ~100 times more massive than those without strong jets. Quasars with more massive black holes are also more clustered, albeit with a weaker correlation, implying that accretion mode differences are less critical in the production of strong jets. Finally, we will present results from the first joint LOFAR-Euclid statistical study on the role of galaxy mergers in triggering quasar radio jets using morphological merger identification from Euclid DR1 data, which reveals the role of small-scale environment in jet production and showcases the potential of future Euclid-LOFAR2.0 synergetic studies.

Speaker: Bohan Yue (University of Edinburgh)

26 Identification of H II Regions through Cross-Matching LOFAR LoTSS DR-3 and WISE Catalogs

H II regions are key tracers of recent star formation and Galactic structure. In this study, we present a method for identifying and characterizing H II regions by cross-matching data from the LOFAR Two-metre Sky Survey Data Release 3 (LoTSS DR-3) and the Wide-field Infrared Survey Explorer (WISE) catalog. Radio emission from LoTSS provides high-sensitivity, low-frequency observations, while WISE mid-infrared data effectively traces warm dust associated with massive star formation. Our analysis reveals a significant number of matches, including both known and candidate H II regions.

Speaker: Patrycja Szybowska

27 Widefield LOFAR-VLBI + Euclid: Selecting dusty, outflowing AGN missed by spectroscopic surveys

Recently, the discovery of so-called ``Little Red Dots'' by JWST has brought the topic of obscured Active Galactic Nuclei (AGN) to the forefront of observational astronomy. Although these systems are potentially quite surprising to see at high redshift, previous studies of obscured AGN have revealed a plethora of populations and properties (red quasars, ERQs, HoTDoGS, etc.). These dusty systems are often suggested to be the missing link in galaxy evolution between dusty starbursts and massive, quenched elliptical galaxies. Unfortunately, these systems make very poor targets for typical optical spectroscopic surveys (eg. SDSS or DESI) due to their relative faintness at similar redshifts and distinct spectral shapes from the general quasar population.

In this talk, we present our new strategy using Euclid Q1 data to identify near-IR AGN candidates and LOFAR-VLBI to pierce through the dust and confirm the presence of an AGN. This approach is similar in spirit to the FIRST-2MASS survey (Glikman et al. 2012) which uncovered an unusually high fraction of quasar outflows, a hint towards this evolutionary link. We explore the effectiveness of this selection in the Euclid Deep Field North, utilising existing spectra, and demonstrate that this AGN population is missed by many existing selection strategies. To improve the selection, we are also working to extend Marco Bondi's work on this field using recent improvements to the LOFAR-VLBI pipeline and combining 4 or more 8-hour observations. We derive suitable near-IR colour and radio flux cuts to enable the application of this selection to the massive Euclid DR1 + LoTSS DR3 dataset to be released next year. This will further be complemented by the ongoing WEAVE-LOFAR survey, which is not biased by reddening.

Speaker: James Petley (Leiden Observatory)

28 Investigating the filamentary emission of radio phoenixes

The properties and structure of magnetic fields in the intracluster medium (ICM) and how cosmic rays are distributed/(re)energised are still open questions in the study of galaxy clusters.
Of late, thanks to sensitive low frequency observations, a new type of extended radio emission is being detected in the ICM, known as radio phoenixes.
Unlike other types of diffuse emission associated with galaxy clusters, phoenixes have a very steep spectrum ($\alpha \ge 1.6$) with an irregular morphology. They are thought to trace old plasma originated from formerly active galaxies that has been re-energised by adiabatic compression due to the passage of a shock wave. However, there is no clear evidence that links phoenixes to shocks.

In this talk, I will present spectral analysis of a couple of radio phoenixes performed combining LOFAR LBA and HBA observations with data at higher frequencies, in order to track a possible spectral curvature and estimate the age of cosmic rays.
I will then focus on the sub-arcsec investigation of the filamentary emission of these sources thanks to LOFAR-VLBI. The surface brightness along the filaments doesn’t follow a clear trend, suggesting these regions are uniformly filled with cosmic rays.
On comparing our results with magneto-hydrodynamical simulations of turbulent dynamo operating in the ICM, I will discuss an emerging scenario suggesting that the filamentary emission is likely tracing magnetic fields intrinsic to the ICM.

Speaker: Nadia Biava (Thüringer Landessternwarte (TLS))

29 Evolution of radio-AGN across cosmic time: new insights from LOFAR Deep Fields

Active galactic nuclei (AGN) can have a significant effect on their host galaxies by regulating their growth or suppressing star formation (known as AGN feedback). Of particular importance for massive galaxies and clusters are jet-mode AGN which display powerful radio jets and keep galaxies ‘red and dead’ once quenched. However, until recently, the cosmic evolution of jet-mode AGN has remained largely unconstrained beyond z~1. The LOFAR Deep Fields survey forms one of the deepest wide-field radio continuum surveys to date: this represents a novel sample to statistically study the evolution of AGN activity and feedback across cosmic time. Using this sample, I will present the first robust measurement of jet-mode AGN feedback out to z ~ 2.5. We discover a new dominant population of jet-mode AGN hosted by star-forming galaxies at high redshifts, that has not been previously observed. I will also present a detailed analysis of the evolution of the host galaxy properties across the bulk of cosmic history, extending to much fainter luminosities and higher redshifts than previous studies. Our results have shown evidence that this new class of AGN within star-forming galaxies is fuelled by a different mechanism compared to their quiescent counterparts. These results showcase the power of deep wide-area radio continuum surveys in the pre-SKA and LOFAR2.0 era in characterising the nature of the faint AGN population across cosmic time.

Speaker: Rohit Kondapally (Durham University)

30 A multi-resolution International LOFAR Telescope view of red and blue quasars in ELAIS-N1

Quasars can be classified as red or blue based on their optical colour. It has been found that the reddest quasars show a significant increase in their radio detection fraction compared to the bluest, and that they appear to be primarily associated with faint, compact radio sources, but the physical interpretation is still being investigated. High-resolution radio observations are essential for constraining the physical extent of the radio emission. In this talk I will present on-going work on a sample SDSS quasars at z < 2.5 in the ELAIS-N1 field, using the recently released deep 144 MHz images at angular resolutions of 6", 1.2", 0.6" and 0.3". These probe nuclear to supergalactic scales simultaneously. Furthermore, LOFAR's excellent sensitivity to faint, diffuse or steep emission allows the detection of emission that other surveys such as FIRST or VLASS, or sparser VLBI arrays potentially could have missed. In this talk, will present initial results on the projected lengths and radio powers derived by combining these four resolutions and compare it against literature findings.

Speaker: Frits Sweijen (Durham University)

31 Echoes from the Edge: Unusual Radio Emission in the Outskirts of Abell 168

Abell 168 is among the lowest mass galaxy clusters known to host multiple-component diffuse radio emission in its outskirts. Previous observations with GLEAM and GMRT revealed two extended radio sources with elongated and circular morphologies, which were classified as radio relics (Dwarakanath et al. 2018). In this study, we present a comprehensive multi-wavelength analysis of Abell 168 using new and archival data from LOFAR, GMRT, MeerKAT, XMM-Newton, and Chandra. Our analysis aims to investigate the origin, morphology, and spectral properties of the diffuse emission. We explore the dynamical state of the cluster and its environment through X-ray imaging and radio spectral mapping. The combined data allow us to test the relic classification and assess alternative scenarios, such as shock-induced emission or revived fossil plasma. This work provides new insights into the nature of diffuse radio sources in low-mass clusters and contributes to our understanding of particle acceleration mechanisms in less energetic environments.

Speaker: Duy Hoang (Thüringer Landessternwarte - TLS)

32 ViCTORIA project: The LOFAR-MeerKAT view of active galactic nuclei in Virgo cluster early-type galaxies

The evolution of active galactic nuclei (AGN) is closely connected to their host galaxies and surroundings. Via feedback processes, AGN can counteract the cooling of the intracluster medium and suppress star formation in their host galaxies. Especially radio observations at low frequencies are able to provide a glimpse into the history of AGN activity, due to the ability to trace old AGN emission. The Virgo cluster, as a substantial reservoir of nearby galaxies, provides an ideal laboratory to study these mechanisms.
To this end we analysed the ACSVCS sample of 100 Virgo cluster early-type galaxies, using unique LOFAR and MeerKAT observations which cover the entire Virgo cluster. The aim of our work was to characterise the AGN population within the Virgo cluster down to low radio luminosities, constrain the AGN duty cycle, and investigate environmental feedback in cluster member galaxies.
In this talk, I will present our results, including a clear correlation between the radio luminosity of AGN and the stellar mass of their host galaxies, as well as indications of a relationship between the angular size and spectral index of the radio emission. I will also discuss two particularly interesting sources, exhibiting very low-surface brightness emission only detectable with LOFAR. For one of those sources - the galaxy M49 - we found an X-ray cavity inflated by its wide-angle tail, which provides new insights into the AGN’s past duty-cyle.

Speaker: Angelina Spasic (Hamburger Sternwarte, University of Hamburg)

33 Evolution of radio AGN up to z~6 with LOFAR

With the availability of new large area and deep 0.3" resolution LOFAR surveys in combination with Euclid imaging, it is now finally possible to carry out large statistical studies of the radio loud Active Galactic Nuclei (AGN) population across cosmic time in combination with host galaxy properties. Whereas previous studies were limited to z~2, constrained by either the depth of observations or the field of view of the instruments, modern facilities such as Euclid and LOFAR allow us to go beyond this border and determine the evolution of the radio-loud AGN population together with their host galaxy properties up to z~6.
With a new sample of 100,000 radio sources, cross-matched with optical data, obtained from the LOw Frequency ARray (LOFAR) Two Metre Sky Survey (LoTSS) Deep Fields, we can for the first time determine the evolution of the radio AGN population out to z~6. Specifically, we study the change in number density of radio AGN for different radio luminosity bins, which shows that AGN with higher radio luminosity peak at earlier times in density compared to their lower luminosity counterpart. Using host galaxy properties such as stellar mass and star formation rate, we investigate the difference in evolution between subpopulations as well and show that at different redshifts, these subpopulations have differing amounts of radio emission. The difference between these populations is interpreted as cosmic downsizing, where the most massive black holes form at earlier times than less massive ones and discuss the importance of our findings in the context of radio AGN feedback.

Speaker: Lars Abbo (Leiden Observatory)

34 The evolution of extragalactic peaked-spectrum sources down to 54 megahertz

Peaked-spectrum (PS) sources, known for their distinct peaked radio spectra, represent a type of radio-loud active galactic nuclei (AGN). Among these, megahertz-peaked spectrum (MPS) sources, which exhibit a spectral peak at a frequency of a hundred megahertz, have emerged as a potential tool for identifying high-redshift candidates. However, the potential evolutionary link between the fraction of these sources and redshift remains unclear and requires further investigation. The recent, high sensitivity Low Frequency Array (LOFAR) surveys enable statistical studies of these objects to ultra-low frequencies (< 150 MHz). In this study, we first use the multiradio data to investigate the evolution of spectral index with redshift for 1,187 quasars from the SDSS 16th quasar catalog. For each quasar, we analyze available data from the LOFAR Low Band Antenna (LBA) at 54 MHz, High Band Antenna (HBA) at 144 MHz, and the Very Large Array (VLA) the Faint Images of the Radio Sky at Twenty cm (FIRST) at 1.4 GHz. We measure the spectral index ($\alpha^{144}_{54}$ and $\alpha^{1400}_{144}$) and find no significant change in their median values with the redshift. Extended sources have steeper spectral indices than compact sources, which is consistent with previous findings. Based on the spectral indices information, we identify MPS sources using these criteria: $\rm \alpha^{144}_{54} >= 0.1$ and $\rm \alpha^{1400}_{144} < 0$, and analyze their properties. We find that the fraction of MPS sources is constant with the redshift ($0.1-4.8$), bolometric luminosity ($\rm 10^{44}-10^{48} erg/s$), and supermassive black hole mass ($\rm 10^{7}-10^{10.5} M_{\odot}$), which suggests that MPS sources have relatively stable physical conditions or formation mechanisms across various evolutionary stages and environments.

Speaker: Sai Zhai (Leiden University)

16:20 Poster viewing + coffee / tea break

Science talks

35 Black hole jets on the scale of the Cosmic Web

Modern, large-area sky surveys at decametre to decimetre wavelengths have begun to reveal the widespread presence of magnetised plasma in the intergalactic medium, transported from SMBHs through relativistic jets. Even more sensitive surveys, such as those possible with LOFAR 2, the DSA-2000, and the SKA, will likely uncover many larger and older plasma deposits, from the Local Universe to the first gigayears. Porphyrion, a recently discovered 7 Mpc long jetted structure that formed in the first half of cosmic time, may provide a glimpse of what future observations will yield. Classically, jet plasma is thought to stay trapped within galaxy clusters and filaments of the Cosmic Web, where diffusion is ineffective. However, systems like Porphyrion appear to demonstrate that jets can carry magnetised plasma all the way into cosmic voids (~90% of the Universe by volume), which are conventionally seen as pristine enough to retain signatures of primordial magnetism.
In this talk, I will discuss observations of Porphyrion and the possibility that voids have been magnetised by Mpc-scale jets, muddling primordial signatures.

Speaker: Martijn Oei (Caltech)

36 Blazars in the LOFAR Era

Blazars have been challenging to study at low radio frequencies due to limited sensitivity and resolution in previous surveys at these frequencies. However, the recent LOFAR surveys; LoLSS-DR1 and LoTSS-DR2, have addressed these issues enabling robust detection of known blazar counterparts. Utilising this, we examine the spectral properties of the blazar population at low frequencies. We follow this up with high resolution LOFAR-VLBI imaging of an X-ray jetted blazar OJ287. The X-ray emission from resolved knots in the jets of many blazars cannot be explained as a simple extension of the radio synchrotron spectrum. So far no general consensus has been reached on the relative dominant contribution of the different broadband-emission mechanisms at play. In particular, observing the low radio frequencies provides valuable constraints to test different emission models like IC/CMB, Synchrotron Self Compton(SSC) or second synchrotron peak. The long international baselines of LOFAR allow us to spatially resolve the individual X-ray emitting jet knots at 140MHz and to probe the previously inaccessible part of the low-energy electron population. In combination with shorter-wavelength radio in uGMRT (600 MHz), the VLA GHz regime and Chandra X-ray data, the LOFAR-VLBI data will help test and constrain the above-mentioned different emission models. Here, we present results from this project with a focus on connecting the low frequency radio to X-ray emissions in the kiloparsec scale knots in the jet. Furthermore, we present broadband SED modeling analysis for these knots, thereby understanding the physical properties of the underlying electron population. Our analysis highlights the potential of low-frequency, high-resolution radio observations to bridge the gap between radio and X-ray regimes in blazar jets.

Speaker: Hrishikesh Shetgaonkar (Julius-Maximilians-Universität Würzburg)

37 Jet reorientation or giant radio blazars - a continuation

In the radio regime, blazars are mostly compact sources. However, at low radio frequencies, we may observe large-scale (several hundred of kpcs) structures. In such a case, two different radio components make up the total radio flux: a flat-spectrum central element and steep-spectrum diffuse pair of lobes, sometimes irregular, plural or misaligned with the jet axis. We interpret their morphologies in the framework of a reorientation of the jet axis related to i.a. episodic jet activity or precession. Here, we present a continuation of the pilot study presented in Pajdosz-Śmierciak et al. 2022: a sample of „extended” blazars viewed by the Lofar Two-meter Sky Survey-V. 2nd Data Release (Shimwell et al. 2022), along with their statistical and physical properties such as total radio power, spectral index or jet realingment timescale. Based on the derived data, jets could change the direction of propagation out of the sky plane during the lifetime of at least some of these sources and with such we may observe morphologically different AGN types simultaneously – similar to the previously discovered giant radio blazar SBS B1646+499 (Pajdosz-Śmierciak et al. 2018). Several plausible origin scenarios are discussed, including i. a. fast jet realignment via Lense-Thirring drag mechanism. From the other hand, we also discussed the possibility that these objects are actually Giant Radio Blazars with rare Fanaroff–Riley I morphology. Hence, the obtained results were compared to the analysis of giant radio galaxies by Dabhade et al. 2020a, 2020b. We find the above interesting not only in the frame of the AGN unification but also, for example, feedback processes and central engines analysis.

Speaker: Urszula Pajdosz-Śmierciak (Jagiellonian University)

19:00 Welcome reception

Tuesday 23 September

Science talks

38 From activation to afterglow: Duty cycles and restarted activity in peaked-spectrum radio sources

Peaked-spectrum (PS) radio sources - Gigahertz-Peaked Spectrum (GPS) and Megahertz-Peaked Spectrum (MPS) - are known to trace the youngest stages of jet evolution. Milliarcsecond VLBI images often reveal compact double morphologies embedded in kpc-scale cocoons, suggesting that many PS objects could later grow into classical FR II or FR I radio galaxies. A key open question is whether this growth is typical or PS activity instead consists of short bursts separated by long quiescent periods remains an open question that can be answered only by detecting relic, low–surface-brightness plasma around the compact cores. Over the last three decades only a handful of PS AGN have been shown to sit inside much older, faint radio cocoons, leaving the duty–cycle of young jets essentially unconstrained. Previous wide-area radio surveys lacked the surface-brightness sensitivity and resolution to recognise these “compact-core + relic/extended emission” systems in statistically useful numbers. LoTSS-DR2/3 changes the landscape with its excellent sensitivity at 144 MHz across the northern sky, exactly the regime where hundred-kiloparsec lobes survive tens of Myr after the jets switch off.
Taking advantage of the high sensitivity and resolution of LoTSS-DR2/3, we examine the duty–cycle of young radio galaxies. The sensitivity and resolution of LoTSS are ideal for unveiling the faint, steep-spectrum cocoons that trace previous jet episodes. We focus on the large LoTSS-area catalogues GPS & MPS sources. The LoTSS images reveal faint, steep-spectrum cocoons that record past jet episodes: so far I have identified 60 PS objects with diffuse emission extending ≥ 50 kpc beyond their unresolved cores. Roughly half reside inside giant radio galaxies that already span megaparsec scales. Coexisting peaked cores and relic/extended emission provide unambiguous evidence of restarted activity; spectral fitting shows that the extended emissions are tens of Myr old, whereas the new cores are younger than a Myr, implying duty cycles dominated by long dormant phases even at low radio powers. In this presentation we will detail the search strategy, analysis pipeline, the current results, and the future work now underway, including optical/IR SED modelling that will probe any synchrony between jet re-ignition and host-galaxy star formation.
By measuring how frequently PS sources carry relics or extended emission beyond core, we can constrain the life-cycle of compact AGN and test whether most eventually mature into large-scale doubles or terminate after brief spurts. These first results demonstrate LOFAR’s unique ability to connect AGN activation to its afterglow, refine models of radio-mode feedback, and deliver the first large, homogeneously selected sample of restarted peaked-spectrum galaxies.
This pilot census also acts as a path-finder: the methods and framework developed here are directly scalable to deeper LOFAR surveys with LOFAR 2.0 and, ultimately, SKA-Low & SKA-Mid surveys, where still fainter afterglows will be detectable in the tens of thousands—opening a new window on the full temporal ecology of radio-loud AGN.

Speaker: Anupama Mohanan (National Centre for Nuclear Research (NCBJ), Poland)

39 Tracing Turbulence and Shocks: LOFAR’s Exploration of Galaxy Cluster Radio Emission

The majority of baryonic matter in the Universe resides as plasma within the large-scale cosmic web, with galaxy clusters representing its densest nodes. These clusters grow through accretion and mergers, processes that inject substantial energy into the intracluster medium via shocks and turbulence. Low-frequency radio observations have revealed that these mechanisms accelerate particles to relativistic energies, producing diffuse synchrotron emission. LOFAR has been pivotal in advancing our understanding of this non-thermal emission, uncovering steep-spectrum, megaparsec-scale radio structures in clusters. Studies of radio relics link these arc-like features to merger-driven shock waves, while radio halos are associated with turbulence and evolving cluster dynamics. Mini-halos, typically found in relaxed clusters, have also been observed to extend well beyond central cores. In addition, LOFAR has revealed new phenomena such as ultra-steep spectrum emission, diffuse radio bridges in pre-merging systems, and large-scale radio envelopes surrounding clusters, highlighting the widespread presence of cosmic rays and magnetic fields. This talk will provide an overview of LOFAR’s key contributions to the study of non-thermal processes in galaxy clusters and outlines prospects for future work.

Speaker: Reinout van Weeren (Leiden University)

40 Revealing the intricacies of radio galaxies and filaments in the galaxy cluster Abell 2255

New generations of interferometers are revealing a wealth of spectacular filaments in the surrounding of radio galaxies, mostly residing in group/cluster environment, whose origin is still unknown. Filamentary structures present new opportunities for studying the physical processes in the intracluster medium, including their magnetic structures and the propagation of cosmic rays. Given the steep radio spectra shown by these structures, deep, low-frequencies observations are necessary to detect them. In this talk, I will present the deepest (56 hours) LOFAR-VLBI observations of filaments in the merging galaxy cluster Abell 2255 at 144 MHz. Going down to sub-arcsecond, we detected and resolved for the first time several filamentary structures related to the tailed cluster radio galaxies, characterizing their morphology and emission at unprecedentedly high-resolution (De Rubeis et al. 2025). These observations prove the potentiality of LOFAR-VLBI for studying these new emerging radio phenomenon. I will then present high-resolution spectral studies, that were possible combining LOFAR-VLBI data with the higher frequencies ones from uGMRT and VLA. With high-resolution (2-3 kpc), we can disentangle the spectral properties of the filaments to study their nature and the interplay between the radio galaxy and the turbulent cluster environment.
I will discuss several formation scenarios regarding the origin of the filamentary emission, involving future updates on this work thanks to new incoming radio and X-ray data, as well as comparison with other similar cases found for other galaxy clusters.

Speaker: Emanuele De Rubeis (Università di Bologna (UNIBO) & Istituto di Radioastronomia (INAF-IRA))

41 First LOFAR LBA View of the Sausage Cluster at 45 MHz

In this talk, I will present the first LOFAR LBA observations of the well-known galaxy cluster CIZA J2242.8+5301 (the “Sausage” cluster), reaching a thermal-noise limited sensitivity of 1.5 mJy/beam at 15″ resolution. This system is not only a benchmark for studying radio relics, but also one of the very few galaxy clusters observed with LOFAR LBA to date. The 45 MHz observations represent the lowest-frequency imaging of this cluster to date, unveiling a complex network of diffuse emission beyond the prominent double radio relics. Focusing on the northern relic, I will show that its surface brightness profile appears remarkably symmetric, in contrast to expected standard sharp-shock plus radiative cooling scenario. To interpret this, we used an analytic model to reproduce the profile incorporating projection effects, magnetic field variations, and shock surface irregularities. These results suggest that additional mechanisms may be at play in producing relic emission, challenging shocks formation models in cluster outskirts. This work also demonstrates the capabilities of LOFAR LBA and its related calibration pipeline for detailed studies of diffuse radio emission, and in particular radio relics, at very-low radio frequencies.

Speaker: Dr Giulia Lusetti (Open University)

42 The Perseus cluster with LOFAR LBA

The Perseus cluster is a nearby, well-studied cool-core galaxy cluster, known to host a radio mini-halo. Recent LOFAR HBA observations have revealed a Mpc-scale giant radio halo, enveloping the mini-halo. The origin of this extended radio emission and the underlying particle (re-)acceleration mechanisms remain poorly understood. By exploring the spectral properties of the radio emission at very low frequencies, we aim to better understand the nature of this radio emission. In this talk, we will present LOFAR LBA images (resolution 17.7” x 15.0”, rms noise of 3.7 mJy/beam) of the Perseus cluster. These observations allow us to investigate whether the radio spectrum of the giant radio halo is consistent with turbulent re-acceleration models, which predict a steeper spectrum than that of the mini-halo. In addition, we study two X-ray ‘ghost cavities’ in the cluster, possibly produced by an older outburst from the central AGN (3C 84), and we discuss whether their radio spectra are consistent with aged AGN plasma. Finally, we present radio images of two tailed radio galaxies in the Perseus cluster (NGC 1265 and IC 310), and discuss the spectral properties along the tails.

Speaker: Christian Groeneveld (INAF - IRA)

43 The radio and optical morphological properties of LOFAR sources in the Euclid Deep Field North

We present a joint analysis of the radio and optical morphological properties of LOFAR sources in the Euclid Deep Field North. Radio sources have been separated into AGN and star-forming galaxies and further subdivided according to their radio appearance (e.g. whether point-like or extended/complex). This information has then been complemented with Euclid/VIS images which provide a snapshot of the merging or isolated status of their host galaxies. We find that radio-AGN are mostly associated with merging systems, with a more marked preference observed for complex radio sources (about 50% vs a mere 15% in the case of association with isolated galaxies). The exact opposite is instead found for star-forming galaxies which mostly reside within isolated systems. Thanks to the exquisite statistics provided by Euclid and LOFAR observations which enable us to analyse samples with different luminosities and belonging to different redshift ranges, we will then discuss what the main drivers for the observed trends are, i.e. whether due to cosmological evolution or radio activity.

Speaker: Manuela Magliocchetti

10:45 Coffee / tea break

Science talks

44 Searching for LOFAR-selected optical/NIR-dark galaxies in the EDFN

The population of massive, dust-obscured galaxies plays an increasingly prominent role in the context of galaxy evolution. These galaxies are considered the progenitors of the passive systems observed at z~3, and they significantly contribute to the cosmic star formation rate (SFR) density at high redshift (z>3). Due to their faintness in optical and near-infrared (NIR) bands, a key challenge is the selection of statistically significant samples of these objects.
Recent studies have shown that an effective approach for identifying these galaxies involves targeting radio-detected sources lacking counterparts in optical/NIR observations. While previous results have mainly been obtained from high-frequency radio data (e.g., 3 GHz), we extend this approach to lower frequencies by leveraging recent deep LOFAR 150 MHz observations in the Euclid Deep Field North (EDFN). Exploiting the Euclid Q1 data release, we identified a sample of 81 sources without detected counterparts up to Euclid/NISP H band.
Combining data from Euclid/VIS and NISP with multiwavelength observations from the Spitzer/IRAC, WISE, Herschel and LOFAR 150 MHz, we aim to derive the physical properties through spectral energy distribution fitting. This includes estimates of their SFRs, stellar masses, and photometric redshifts. Finally, we plan to infer their contribution to the SFR density and compare our results with those from NIR-dark samples selected using higher-frequency radio data. This comparison will allow us to investigate potential differences in redshift distribution and assess their position relative to the Main Sequence of star-forming galaxies.

Speaker: Marika Giulietti (IRA-INAF)

45 From clusters and groups to the cosmic field: environmental drivers of AGN evolution in LoTSS DR2

In this talk, I will present a systematic study of how large‐scale environment influences the triggering and evolution of radio AGN. Using LOFAR observations at 144 MHz, we cross‐match a sample of more than 200.000 AGN from LoTSS DR2 with optical group and cluster catalogs to define subsamples of field, group and cluster AGN. A spectroscopic subset is also classified into HERGs and LERGs.

We find that, in the low‐power regime ($L_{144 \rm MHz} < 10^{22}$ W Hz$^{-1}$), field AGN dominate the population, indicating that high‐density halos might suppress the onset of low‐luminosity radio activity. Group and cluster AGN become significant only above this threshold.

At intermediate powers ($10^{22}

In the high‐power regime ($L_{144 \rm MHz} > 10^{26}$ W Hz$^{-1}$), powerful HERGs are found exclusively in the field, implying that the most energetic radiative AGN activity is likely fueled only by mergers outside of dense halos.

Radial distribution analysis shows that LERGs occupy the full extent of clusters, while they concentrate within $\sim$60 kpc from the centre of groups, consistent with jet‐mode feedback fueled by hot intra-group gas. HERGs are instead uniformly distributed out to $\sim$200 kpc in both groups and clusters, with cluster HERGs showing elevated densities at larger radii, which might be indicative of merger‐driven cold‐gas accretion.

These findings support the hypothesis that hot gas in groups and clusters promotes kinetic, low‐efficiency modes, while cold‐gas availability in the field enables high‐efficiency radiative modes. We conclude that both halo mass and conditions of the local gas play a fundamental role in modulating AGN fueling and accretion and regulating feedback.

Speaker: Thomas Pasini (Istituto di Radioastronomia IRA-INAF)

46 The Fraction of Radio-Loud AGN in the Euclid Deep Field North

Understanding how active galactic nuclei (AGN) evolve with cosmic time and interact with their host galaxies is central to constraining the role of AGN feedback in galaxy evolution. In the era of deep, wide-field sky surveys, it is now possible to statistically characterise the relationship between radio AGN activity and host galaxy properties across the full AGN population. We investigate the fraction of radio-loud AGN as a function of redshift and stellar mass by combining observations from LOFAR with data from the Euclid space telescope. Previous research on radio sources in the local universe (z < 0.3) has identified a clear and steep power-law dependence of the radio-loud AGN fraction on the stellar mass. Using new data in the Euclid Deep Field North (EDFN), the existing LOFAR radio source catalogue, comprising 23,309 sources, is cross-matched with the Euclid Q1 data release to identify optical counterparts and obtain physical parameter estimates. This enables an extension of the radio-loud AGN fraction out to z = 3 and down to stellar masses of 10⁹ $M_☉$—a regime not previously accessible. The combined sensitivity and spatial resolution of Euclid and LOFAR enable the most robust statistical analysis of the radio-loud AGN fraction to date. We find that the power-law relation flattens significantly at lower stellar masses, indicating a departure from previously established trends. This transition suggests a connection to a change in the AGN accretion mode from a hot, radiatively inefficient mode at higher mass to a mode corresponding to cold gas accretion, triggered by galaxy mergers and interactions in under-dense environments. These findings offer new constraints on AGN-galaxy co-evolution models.

Speaker: Mr Scott Visser (PhD Candidate at the Leiden Observatory, Leiden University)

47 The largest samples of radio-luminous AGN from wide-area LOFAR surveys

The wide-area LOFAR surveys combined with deep optical data offer an unprecedented opportunity to characterize and model the radio-luminous AGN population, which are thought to play an essential role in the evolution of the most massive galaxies. I will discuss the latest results on the selection of this AGN population and what we can learn statistically about host galaxies, environments and environmental impact from samples of hundreds of thousands of objects. I will also discuss the future progress in this area that can be expected from LoTSS DR3 and Euclid data.

Speaker: Martin Hardcastle (University of Hertfordshire, UK)

48 The LOFAR view of the EDFN

The Euclid Deep Field North (EDFN), located at RA=269.73 deg and
Dec=+66.02 deg in the North Ecliptic Pole (NEP) region, is the fourth
field of the LoTSS Deep Field project, and the only deep field in the
northern sky to be observed by the Euclid mission.
The Euclid satellite will cover the circular shape 20 sq deg of the
EDFN with multiple passes providing high-resolution near-IR imaging
(~0.3 arcsecond) down to the full depth of H=26 by DR3.
In this talk I will present an overview of the LOFAR observations on the EDFN, focusing on the status of the data processing, the images and catalogues available, and some of the results obtained so far imaging the EDFN with an angular resolution ranging from 6" down to ~0".3.

Speaker: Marco Bondi (INAF-IRA)

49 The LOFAR Two-metre Sky Survey

The LOFAR Two-metre Sky Survey is a deep low frequency survey of the northern sky. We are preparing to release LoTSS-DR3 which consists of images and data products covering about 90% of the northern sky. These data products were created from 13,000hrs (or 19PB) of observations and took around 20 million CPU core hours to produce. The survey images contain over 13.7 million sources and typically have a sensitivity of 0.1mJy/beam at a resolution of 6arcseconds.

In this talk I shall provide an update on LoTSS including survey progress, challenges, plans for the upcoming data release and ambitions to build upon LoTSS once the LOFAR2.0 upgrade is complete.

Speaker: Timothy Shimwell (ASTRON)

13:00 Lunch break

Observatory Session: Building the LOFAR2.0 Observatory

Convener: R. Pizzo

50 Welcome

Speaker: R. Pizzo

51 The LOFAR2.0 Observatory: vision

Speaker: M. van Haarlem

52 Developing the LOFAR2.0 observing capabilities

Speaker: W. van Cappellen

53 Developing the LOFAR2.0 data processing system

Speakers: V. Impellizzeri, L. Morabito

54 Scientific & Technical Committee - link to the users community

Speaker: R. van Weeren

15:25 Coffee / tea break

Observatory Session: Commissioning and Operating the LOFAR2.0 Observatory

Convener: I. van Bemmel

55 Operating the LOFAR2.0 observatory

Speaker: R. Pizzo

56 LOFAR2.0 commissioning & commissioning areas

Speakers: M. Brentjens, E. van der Wateren, C. Cordun, E. Orru, B. Asabere, T. Shimwell, M. Iacobelli

57 LOFAR2.0 Processing Pipelines

Speaker: T. Shimwell

58 Lightning talks - commissioning results

Speaker: Commissioners

Wednesday 24 September

Science talks

59 Probing AGN spectral indices with Apertif and LOFAR

We present two new radio continuum images obtained with Apertif at 1.4 GHz. The images, produced with a direction-dependent calibration pipeline, cover 136 square degrees of the Lockman Hole and 24 square degrees of the ELAIS-N fields, with an average resolution of 17x12" and residual noise of 33 uJy/beam. With the improved depth of the images we found in total 63692 radio sources, many of which are detected for the first time at this frequency. With the addition of the previously published Apertif catalog for the Bootes field, we cross-match with the LOFAR deep-fields value-added catalogs at 150 MHz, resulting in a homogeneous sample of 10196 common sources with spectral index estimates, one of the largest to date. We analyze and discuss the correlations between spectral index, redshift, linear sources size, and radio luminosity, taking into account biases of flux-density-limited surveys. Our results suggest that the observed correlation between spectral index and redshift of active galactic nuclei can be attributed to the Malmquist bias reflecting an intrinsic relation between radio luminosity and the spectral index. We also find a correlation between spectral index and linear source size with more compact sources having steeper spectra.

Speaker: Alexander Kutkin (ASTRON)

60 The LOFAR LBA Sky Survey: second release and plans for LFOAR2

The LOFAR Low Band Antenna (LBA) system makes LOFAR the only telescope capable of ultra-low frequency (<100 MHz) observations at high resolution. Working at these frequencies is challenging due to the low signal-to-noise ratio and ionospheric disturbances. Developments in the calibration strategies allowed us to reach thermal noise and even attempt <30 MHz imaging and long-baseline imaging.

In this talk, I will make an overview on the upgrades made to the Pipeline for LOFAR LBA (PiLL). The strategy is being successfully used in an increasing number of publications, and it is important for the LOFAR community to know its performance, improvements, and limitations. I will also give a status update on the LOFAR LBA Sky Survey (LoLSS), that aims to cover the sky at dec > 24 deg in the frequency range 42-66 MHz, reaching the sensitivity of 1 mJy/b and the resolution of 15 arcsec. At the moment, the data reduction of the 1974 fields has started and several images per day are being prepared. When the process will be finished, the data will be internally and then publicly released as LoLSS-DR2. Finally, I will outline the plans for the expansion of the LBA surveys with LOFAR 2.0 through the LBA LOFAR Community Sky Survey (LLoCuSS) project.

Speaker: Francesco de Gasperin (IRA INAF)

61 Reprocessing the Full LOTAAS Survey with Improved Methods: Paving the Way for Commensal LOFAR 2.0 Transient Searches

LOTAAS, the LOFAR Tied-Array All-Sky Survey, offers an extensive dataset for discovering low-frequency radio transients. However, the original single-pulse search was not optimized to detect longer-duration or heavily scattered signals, and was limited by high false positive rates arising from instrumental variability and RFI. Since then, our understanding of FRBs at low frequencies has significantly advanced. In particular, two repeating sources have now been detected with LOFAR, demonstrating that low-frequency emission is indeed produced in some FRBs and can escape their local environments. Meanwhile, surveys at higher frequencies continue to reveal a population of highly scattered FRBs and long-period transient sources, raising the possibility that similar signals remain undetected in the LOTAAS data.

In this talk, I present the reprocessing of the LOTAAS survey using updated methods tailored to this new landscape. A central component of this work is “flat-fielding,” a normalization technique we introduce to suppress beam-to-beam gain variations and reduce the impact of persistent RFI across the array. This is done by dividing each beam by the average of the central beams within a sub array pointing, effectively flattening the instrumental response across frequency and time while preserving astrophysical signal morphology. This significantly lowers the false positive rate—by several orders of magnitude—and improves the reliability of single-pulse detection. Additionally, the pipeline improves sensitivity to wide and scattered bursts and is designed to process data efficiently at scale. I’ll highlight early results from reprocessed beams and discuss how this method provides a path forward for scalable transient detection in future datasets, specifically through the EuroFlash cluster for LOFAR 2.0.

Speaker: Cees Bassa (ASTRON)

62 Nearby galaxies with LOFAR

In recent years, the study of nearby galaxies at low radio frequencies has seen significant progress, largely driven by the capabilities of the Low-Frequency Array. Both targeted observations and wide-field surveys, such as the LOFAR Two-metre Sky Survey, have provided unprecedented insights into the properties of galaxies in the local Universe.
This talk will present the work of the LOFAR Nearby Galaxies Working Group. We showcase results spanning a range of topics, including the calibration and refinement of the low-frequency radio–star formation rate relation, and the role of cosmic rays and magnetic fields in galaxy evolution. Emphasis is placed on how LOFAR observations contribute to our understanding of the interplay between star formation, energetic particle transport, and magnetic field structures, and their importance in constructing a comprehensive picture of galaxy physics

Speaker: Rosita Paladino (INAF- Istituto di radioastronomia)

63 The low-frequency radio-star formation rate relation in nearby galaxies

Radio continuum emission has the potential to be an extinction-free star formation tracer in galaxies near and far. Low-frequency radio continuum observations can give us new insights into the workings as well as the limitations of the radio-star formation rate (radio-SFR) relation. We used maps from a sample of nearby galaxies including both low- and high-band data from the LOw Frequency ARray and ancillary data in the radio continuum and infrared. Studying the radio-SFR relation at low frequencies we find deviations from the simple power-law spectrum that we would expect for a calorimetric cosmic-ray electron spectrum. In particular we find a super-linear radio-SFR relation, where the more massive galaxies are better electron calorimeters than their lighter counterparts. This can be judged on the basis of the radio spectral index where less massive galaxies have flat spectra in contrast to more massive galaxies that have steep spectra. We were able to calibrate the influence of the radio spectral index with spatially resolved observations and show that the global and local radio-SFR relation can be unified. Then, with ultra-low frequency observations we explored absorption processes in star-forming regions. We demonstrated that both ionisation losses of cosmic-ray electrons in the neutral medium and free-free absorption of radio continuum radiation in the ionised medium play a role in the shaping the radio continuum spectrum. This may potentially limit the use of radio continuum as a star-formation tracer below 100 megahertz.

Speaker: Volker Heesen (Universität Hamburg)

64 Cosmic ray electron propagation and the radio-IR correlation in IC342

We present a detailed multi-frequency study of the resolved radio--far-infrared (FIR) correlation in the nearby spiral galaxy IC342 (3.3 Mpc), using new LOFAR 144 MHz observations and archival VLA data at 1.4 and 4.8 GHz, combined with Herschel PACS and WISE infrared maps. After isolating synchrotron emission via thermal/nonthermal separation using $22\mu$ m emission, we analyze spectral indices and derive magnetic field strengths under equipartition. We find synchrotron spectral flattening at low frequencies ($\alpha_{0.14-1.4} = -0.51$ vs. $\alpha_{1.4-4.8} = -1.06$), consistent with aging or low-frequency absorption. Equipartition estimates yield average total fields of $\sim$10~$\mu$G and $B_\text{ord}/B_\text{tur} \sim 0.2$ in star-forming regions. A wavelet-based multiscale correlation analysis reveals a break scale in the radio--FIR correlation at $\sim$200 pc (1.4 GHz) and $\sim$320 pc (144 MHz), interpreted as CRE diffusion lengths. The inferred diffusion coefficient ($D \sim 10^{26}$ cm$^2$ s$^{-1}$) is lower than Galactic averages, implying slower transport or significant escape. We test two CRE propagation models: (i) pure diffusion and (ii) diffusion with escape. The latter yields a tighter match across a sample of galaxies, including IC~342, indicating that turbulent diffusion and vertical escape both shape CRE transport. Moreover, we find a strong positive correlation between diffusion length and ordered magnetic field strength, supporting a contribution from streaming propagation along magnetic field lines. Our results demonstrate that a combination of turbulent diffusion, escape, and possible streaming governs CRE propagation, and must be considered in models linking synchrotron and FIR emission in star-forming galaxies.

Speaker: Prof. Fatemeh Tabatabaei (School of Astronomy, Institute for Research in Fundamental Sciences (IPM), PO Box 19395-5531, Tehran, Iran)

10:45 Coffee / tea break

Science talks

65 Cosmic ray measurements with LOFAR, and the road to SKA

Since taking its first cosmic ray data in 2011, LOFAR has demonstrated the potential of radio measurements of cosmic ray air showers. With analysis techniques developed along the way, high-precision results on their primary energy and the depth of shower maximum became available, putting the radio technique in line with the state of the art in this field.

In this talk I will review the LOFAR results on cosmic rays, discuss the plans for making use of the new capabilities of LOFAR 2.0, and present simulation results for the next big radio telescope, the SKA.

With the SKA-Low radio telescope currently being built in Australia, the opportunity arises to detect cosmic rays with an antenna array that is over an order of magnitude more dense. It has nearly 60,000 antennas in a circle of 1 km diameter.
I will show recent results of applying the techniques developed to maturity for LOFAR to a detailed simulation study for SKA.
This serves as a baseline for the performance of SKA; new analysis techniques are being developed that aim to fully exploit the wealth of data from SKA antennas.

Speaker: Arthur Corstanje (Vrije Universiteit Brussel)

66 An overview of the cosmic-ray particle detector array at LOFAR

Have you ever been to the LOFAR superterp and noticed the black boxes spread across the grass there? In this contribution, I will give an overview of the particle detectors these boxes house, and the fundamental role they play in cosmic-ray detection at LOFAR.

When a cosmic ray enters the atmosphere it initiates a cascade of particles called an air shower. This cascade generates a sharp pulse of radio emission that can be observed with the LOFAR antennas. We have demonstrated that this radio signal can be used to reconstruct critical information about the cosmic rays that gives us clues about their origin. The particle detectors installed at the superterp are what makes this observation mode possible.

Firstly, by detecting the air shower particles that reach ground level, the particle detectors provide a means with which to trigger antenna data readout that is necessary for cosmic-ray observation. Secondly, the data collected by the particle detectors provide an independent means of reconstructing air showers, offering a complementary view of air shower development. I will discuss the operation of the LOFAR particle detectors over the last decade, the recent expansion of the array, and prospects for extracting new science from the detectors going forward in the LOFAR 2.0 era.

Speaker: Katie Mulrey (Radboud)

67 Signature of the local structures in Low-Frequency Radio Observations

The LOw-Frequency ARray (LOFAR) offers an unprecedented opportunity to study the magneto-ionised medium of the Milky Way. In this talk, I will present two mosaics constructed from the second data release of the LOFAR Two-Metre Sky Survey (LoTSS-DR2), which trace polarised synchrotron emission in the high-latitude inner and outer Galaxy. We associate the dominant observed structures with Loop III and the Local Bubble, providing new insight into the local interstellar environment.

We estimate the minimum distance to the Faraday structures associated with the Local Bubble to be 40–80 pc. The observed Faraday depth gradient suggests a connection to the curvature of the Local Bubble boundary. By comparing our results with existing models, we propose that, in addition to the shell, we may also be detecting contributions from the complex of local interstellar clouds (CLIC) residing within the cavity.

Speaker: Vibor Jelic (Ruder Boskovic Institute)

68 Magnetic fields in dense molecular cores: a new perspective from meter-wavelength radio data

Magnetic fields in dense starless cores are crucial for understanding the formation of stars, as these molecular cores mark the initial gravitationally bound stage in the star-formation process. Typically, these cores accumulate gas from their molecular cloud environment until they overcome magneto-turbulent support and collapse into protostellar objects. Traditional studies of magnetic fields in these cores have primarily used indirect methods, such as infrared dust polarization and molecular-line Zeeman splitting. However, these methods have significant limitations.

In this talk, I propose a novel technique complementary to the infrared band, utilizing non-thermal synchrotron emission detectable in the radio spectrum to trace magnetic fields in dense cores. This approach builds on theoretical studies suggesting that cosmic-ray electrons interacting with magnetic fields can produce detectable synchrotron radiation at low radio frequencies (Padovani+2018). I will present an extensive statistical analysis using the LOFAR telescope at 144 MHz, focusing on the median stacking of a large sample of more than 300 prestellar cores in the Perseus molecular cloud (Bracco+2025). While we only achieved upper limits on magnetic field strengths on the order of 100 uG—due to current telescope sensitivity—this method promises a new avenue for studying magnetic fields in molecular clouds with upcoming advanced radio telescopes like LOFAR-ERIC and the Square Kilometer Array, which could detect such emissions within a few hours of observation.

Speaker: Andrea Bracco (INAF - OAA, LPENS)

69 Detections of Carbon Radio Recombination Lines with the NenuFAR telescope

In this talk, I will present our work with the data from the Long-Term 10 program of the newly commissionned NenuFAR telescope in Nançay. This program aimed at observing radio recombination lines (RRLs) between 10 and 85 MHz in absorption in various Galactic lines of sight. I will present the results we obtained observing towards Cassiopeia A, Cygnus A, and Tau A. For each of these lines of sight, we used the beam-forming mode, and we integrated several tens of hours. The nominal spectral resolution was 95.4~Hz, and the frequency range was 10-85 MHz. We built and applied a reduction pipeline, mostly to remove RFI contamination and correct the baselines. We also fitted the Carbon RRLs (CRRLs) associated to various line-of-sight clouds. Indeed, the line variation with the electronic quantum number provides constraints on the physical properties of the clouds: the electron temperature Te, the electron density ne, as well as the temperature of the radiation field T0, the mean turbulent velocity and the typical size of the cloud. Cas A and Cyg A are the brightest sources in the sky at these frequencies, and were already observed by LOFAR, so we used them to benchmark our methodology. In these sources, we improved the signal-to-noise ratio (SNR) and spectral resolution compared to LOFAR observations. We detected 398 Calpha lines (out of 443 theoretically comprised in this frequency range) towards Cas A. Globally, our final constraints slightly differ from those inferred from LOFAR results, which we could relate to the large beam-size of NenuFAR. I will then present the first detection of CRRLs towards Taurus A. In order to identify line-of-sight clouds, we used complementary tracers: CO, HI and dust. Our analysis revealed several spatially separated velocity components in the line-of-sight, shedding light on the organisation of the multiphase ISM. Finally, I will finally present numerous perspectives opened up by our studies: detections of higher order transitions (beta, gamma, etc.), of other species (H, He, etc.) and of other Galactic environments.

Speaker: Lucie Cros (LPENS)

20:00 Conference dinner

Thursday 25 September

Science talks

70 Spectral features and scintillation studies of Cas A from low-frequency observations with NenuFAR

The supernova remnant Cassiopeia A plays a unique role in radio astronomy and astrophysics and is currently being explored in various ways. We present recent developments in NenuFAR observations applied to Cas A at low frequencies. Beginning in 2019, the GURT one-baseline interferometer established the continuous radio spectrum of Cas A at 16–74 MHz, using Cyg A as a calibration source. Based on spectral results, data analysis provided an opportunity to estimate the absorption parameters of ionized gas both inside and outside the supernova remnant.
Subsequent studies continued in 2023, based on simultaneous observations conducted with the help of two different radio telescopes, URAN-2 and NenuFAR. The instruments were configured as one-baseline interferometers, and their spectral measurements were combined from two segments, covering the frequency range of 8–66 MHz. This is particularly significant because the spectral maximum of low-frequency radiation is located at approximately 21 MHz.
Considering long-term observations of Cas A's radio emission, including the most recent ones, we have noticed that the spectral peak frequency has changed over time. This effect is driven by the interaction between the supernova remnant and its surrounding interstellar medium.
Next, we utilized the more extensive capabilities of the NenuFAR radio telescope in multi-baseline interferometric mode. Observations were carried out from May to September 2024 during a period of high solar activity, and their records were subject to intensive scintillation. These observations have enabled investigations into both the integral continuous spectrum of Cas A and the power spectrum distribution of scintillation, caused by irregularities in the ionosphere and possibly in the interplanetary medium. The recent results complement previous research very well.
We thank the National Research Foundation of Ukraine for its financial and organizational support under the call “Excellent Science in Ukraine” (2024–2026), Grant No. 2023.03/0007.

Speaker: Lev Stanislavsky (Junior Researcher, Institute of Radio Astronomy, Kharkiv, Ukraine)

71 The deepest radio image using the full European LOFAR

In recent years, we have established a robust strategy for producing sub-arcsecond (wide-field) images using the full European LOFAR array (Morabito et al. 2022; Sweijen et al. 2022). These high resolutions reduce confusion noise, making it possible to create ultra-deep images by combining multiple LOFAR observations. However, this comes for wide-field imaging with substantial computational costs (e.g. de Jong et al. 2024). To address this, we revisited our data processing strategies and introduced techniques for handling large data volumes more efficiently. This has led to a reduction in computational cost up to a factor of 15, alongside the implementation of improved calibration methods that enhance image fidelity as well (de Jong et al. 2025; de Jong et al. submitted). These developments have enabled the creation of the deepest radio image to date, achieving a central RMS sensitivity of 6 μJy/beam across a 2.5 x 2.5  degrees field of view at 0.3" resolution, using 200 hours of LOFAR observations.

In this talk, I will present the key developments that enabled the creation of this record-breaking image. I will also highlight future directions, including ongoing efforts to fully automate the LOFAR VLBI pipeline for wide-field imaging and how to further reduce computational costs. These advancements will pave the way for ultra-deep high-resolution studies of the radio sky at 150  MHz.

Speaker: Jurjen de Jong

72 From Radio to Optical: Streamlining Source Identification in LoTSS DR3

The LOFAR Two-metre Sky Survey (LoTSS) Data Release 3 (DR3) now surpasses its predecessor, DR2, in both scope and source count—covering nearly 90% of the northern sky and revealing millions of new radio sources. Identifying optical and infrared counterparts to these sources is essential for determining their properties (e.g. redshift, morphology, luminosity) and enabling further scientific analysis.

While DR2 cross-matching relied on a combination of statistical techniques and citizen science, the scale of DR3 demands a more efficient and scalable approach. This talk presents a new cross-matching pipeline developed to complement the original DR2 methodology. I will outline current automated techniques used to reduce reliance on manual inspection and discuss ongoing efforts to integrate LoTSS DR3 with new optical/IR data from the Euclid mission.

Speaker: Bonny Barkus (University of Hertfordshire)

73 A decade of sub-arcsecond imaging with the International LOFAR Telescope (and a look to the future)

Sub-arcsecond imaging with the ILT has become more accessible over the last decade, thanks to efforts to build a publicly available pipeline using LOFAR-specific tools, which has resulted in a dramatic increase in the number of publications. The ILT's combination of resolution, field of view, and low observing frequency make it a unique instrument for a wide range of scientific applications, and it will remain unparalleled even in the era of the Square Kilometre Array Observatory. In this talk I will provide an overview of the technical considerations and calibration methods for sub-arcsecond imaging with the ILT. I will demonstrate the unique capabilities unlocked by sub-arcsecond imaging with the ILT, using examples from the literature. I will summarise the current state of our technical capability as it relates to the LOFAR2.0 Large Programs, and outline ongoing and future developements.

Speaker: Leah Morabito (Durham University)

74 LoTSS-HR: The high-resolution post-processing of the LOFAR Two-Metre Sky Survey

The LOw Frequency ARray (LOFAR) is one of the world's leading observatories at low radio frequencies. With its pan-European baselines reaching up to 2000 km in length, it is capable of achieving a sub-arcsecond angular resolution at frequencies below 200 MHz. However, the use of its international baselines has been hindered for most of the current lifetime of the observatory due to technical and logistical challenges: its phased-array design, the ionosphere and lacking software tools. For this reason, many projects, including the LOFAR Two-Metre Sky Survey (LoTSS), have relied only on the Dutch part of the array, using baselines up to 120 km. Thanks to the Long Baseline Working Group, a strategy has been developed to enable the calibration of the international stations. This has unlocked the highest resolutions (~0.3 arcseconds) attainable with LOFAR, enabling a wide variety of research for the first time. Equipped with the newly-developed LOFAR-VLBI pipeline, we have been working on following up LoTSS by post-processing the archival LoTSS data to obtain high-resolution (0.3") images of all reasonably bright sources within the Field of View of each pointing. Currently, we are finishing up Data Release 1 of LoTSS-HR, which is based on 30 LoTSS fields and will include the release of around 5000 high-resolution LOFAR images to the public. In this talk, I will give an overview of the LoTSS-HR project and its upcoming Data Release 1, including the details of the calibration strategy, the current results of the project and the future outlook.

Speaker: Roland Timmerman (Durham University)

75 Initial Results from Transient Searches in the LOFAR Two-Metre Sky Survey

Long-period transients (LPTs) are a recently identified class of coherent radio transients with durations ranging from a few seconds to several minutes, and periodicities on timescales of minutes to hours. To date, only nine such sources have been reported, with few confirmed to reside in white dwarf–M-dwarf binary systems. The absence of detected optical companions or detection of X-rays in other cases leaves open alternative interpretations, including a possible magnetar origin. Identifying more LPTs is critical to constraining the population and evolutionary pathways of slowly rotating neutron stars and white dwarfs. In this work, we present results from a systematic search for long-period transients and other coherent radio bursts using data from the LOFAR Two-Metre Sky Survey (LoTSS). We report the discovery of an LPT with a 125.5-minute period, associated with a binary system containing an M-dwarf companion. We also present the initial results and highlight other transient candidates identified in the first 10% of the LoTSS Data Release 1 (DR1) fields, offering new insights into the dynamic radio sky. This project serves as a benchmark for transient search methodologies with LOFAR 2.0 and lays the groundwork for the upcoming EuroFlash project, which aims to enable real-time detection of radio transients.

Speaker: Reshma Anna Thomas (ASTRON)

10:45 Coffee / tea break

Science talks

76 Transients in the image plane with LOFAR2.0

Radio transients in the image domain are currently undergoing a big revolution, with exciting new discoveries from radio telescopes around the World including from LOFAR. Key highlights from LOFAR include the detection of the first candidate coherent radio transient following a gamma-ray burst and the first identification of a source of the new class of long period Galactic transients.

In this talk, I will give an overview of the key results and projects underway searching for image plane transients with LOFAR. I will outline the projects we will conduct for LOFAR2.0 with rapid response triggers, and fully automated fast imaging and transient processing on the LOFAR2.0 Science Data Centre. I will describe our work in collaboration with the EuroFlash team to create a real time image plane transient detection system for LOFAR2.0. Finally, I will introduce the upcoming AARTFAAC2.0 and outline the exciting results we hope to obtain from it.

Speaker: Antonia Rowlinson (University of Amsterdam & ASTRON)

77 Detecting radio transients with LOFAR using LoTSS

We recently opened a new window into the variable radio sky on timescales of seconds to minutes. Through these observations, a new class of sources Long Period Transients (LPTs) has begun to emerge. These transients emit previously unknown radio flares lasting from seconds to minutes and exhibit periodicities ranging from minutes to hours. Such timescales suggest that these transients produce coherent radio emission. Some have been associated with high-energy counterparts in the Milky Way, suggesting a magnetar origin, while others have been identified as M dwarf–white dwarf binary systems, including one detected in LOFAR data. However, their nature remains uncertain, and more detections are needed to constrain these hypotheses and improve our understanding of the origin of LPTs.

Here, we present our ongoing analysis of the LOFAR Two-Metre Sky Survey (LoTSS) data. LoTSS aims to image the entire northern sky with unprecedented sensitivity and angular resolution, probing a largely unexplored region of the radio sky. Our approach uses modern imaging techniques, including subtraction imaging and fast filter analysis, to detect rare bursts using 8-second and 2-minute snapshot images. We also introduce a new de-dispersion technique developed for LOFAR images, aimed at detecting fainter, dispersed signals. This technique will be applied for the first time to approximately 3,000 LoTSS fields.

Over the next few months, our goal is to analyze more than 20% of the available data to detect additional LPTs. This project will contribute to the development of LOFAR 2.0 and the Euroflash project, supporting efforts to accelerate the real-time identification of these transients.

Speaker: Sylvain Ranguin

78 Fast radio bursts: the LOFAR bass notes

Over the past decade, our understanding of fast radio bursts (FRBs) has greatly increased. We have now discovered thousands of these millisecond-duration, extragalactic bursts, and have localised over a hundred of them to their host galaxies. While at least some FRBs appear to come from the ultra-magnetised neutron stars known as magnetars, the diverse locations and properties of FRBs suggest that this isn't the complete answer. Low-frequency detections of FRBs, below 300 MHz, have been elusive. To date, only two FRB sources have been detected at 150 MHz, both using LOFAR. Despite the challenges in finding them, low-frequency detections provide valuable insights about the FRB phenomenon because propagation effects are particularly pronounced at these frequencies. One LOFAR-detected FRB exhibits periodic activity, with the LOFAR bursts arriving later in the cycle. This source may be an interacting binary system. The other LOFAR-detected FRB is found in a low-density plasma environment that strongly contrasts with that seen from other repeating FRB sources. Is this FRB in a cleaner environment because it is older than others or because it has a different physical origin? In addition to explaining what we have learned from these two sources, I will summarise ongoing and upcoming efforts to detect FRBs using LOFAR. These include beam-formed searches through the LOTAAS survey, image-plane searches in the LoTSS survey, and dedicated follow-up beam-formed observations of known repeating FRBs. I will discuss how even in the absence of detections, low-frequency observations enable us to place valuable constraints on the burst rates and the local environments of these enigmatic sources. The repetition rate limits derived from these searches can guide future low-frequency follow-ups with instruments like LOFAR2.0, SKA-Low, and NenuFAR, paving the way for deeper insights into the nature of FRBs.

Speaker: Akshatha Gopinath (University of Amsterdam)

79 When Satellites Speak Loudly: Polarized Starlink Emission Below 100 MHz Seen by NenuFAR

The rapid expansion of satellite mega-constellations, such as Starlink, presents new challenges to low-frequency radio astronomy. In this talk, I present results from NenuFAR observations revealing strong and highly polarized radio emissions from Starlink satellites below 100 MHz. I will discuss the observational signatures, potential origin of the radiation, implications for calibration and RFI mitigation, and how this work contributes to our understanding of satellite interference in the emerging era of dense orbital activity.

Speaker: Xiang Zhang (Observatoire de Paris)

13:00 Lunch break

Science talks

80 Near-field satellite detection using LOFAR and GRAVES

This research looks at the feasibility and technicalities of using the Low Frequency Array (LOFAR) as a method for detecting and tracking satellites and space debris. It will consider using LOFAR as the receiver in a passive bi-static solution with the French GRAVES space radar as emitter to observe and identify objects in Earth orbit.

Based on Lunar reflections of GRAVES' emissions detected with LOFAR, this research determined the GRAVES system total emission power and scanning beam period. A single Remote LOFAR station is capable of detecting reflected signals from an object with an RCS of 1 m$^2$ at a distance of 2000 km and can detect objects with an RCS of 5 m$^2$ at a distance of 3000 km. This renders a single LOFAR station capable of detecting 36% of all known objects in Earth orbit with an instantaneous observation with a S/N > 2. Orbital parameters of radius and inclination can be fitted based on available Doppler-shift data with an accuracy of $\pm$ 0.3 degrees for inclination, and $\pm$8 km in terms of radius. Using more ground stations will improve the result.

Using the LOFAR system in a bi-static configuration as a receiver for GRAVES' radar reflections is a viable method for the Netherlands to gain access to space situational awareness data, without having to build an emitter itself.

Speaker: Floris Martens (Leiden University / ASTRON)

81 Navigating the spectrum: regulatory realities and RFI challenges for LOFAR

While not a science talk, this presentation aims to provide an overview of the regulatory landscape and technical approach to protect LOFAR in an increasingly crowded radio spectrum. I will introduce the basics of spectrum management, including the international landscape that governs radio frequency use, and the role of CRAF in protecting radio astronomy. The talk will also explain how compatibility studies are used to assess potential interference from new spectrum users. Finally, I will discuss a number of emerging challenges that are particularly relevant to LOFAR operations, such as the impact of wind turbines, unintended radiation of satellites, and wireless power transfer. Spectrum management is rarely discussed in radio astronomy conferences, but it is crucial for safeguarding our observational capabilities now and into the future.

Speaker: Emma van der Wateren (ASTRON)

82 RISER – High-Resolution Visualisation of the Inner Heliosphere Using LOFAR

Observations of interplanetary scintillation (IPS) offer a way to provide global measurements of the inner heliosphere using ground-based systems. LOFAR offers capabilities in this area beyond those of other instruments, visualising the turbulence giving rise to IPS during the passage of a Coronal Mass Ejection and associated with the tail of a comet.

Since March 2025 the LOFAR-UK Rawlings Array has been used full time for measurements as part of the RISER (Radio Investigations for Space Environment Research) project, recording over 100 observations per day IPS, distributed across the inner heliosphere, which are subsequently analysed to produce estimates of velocity and ‘g-level’, a measure of the strength of scintillation, related to density. These analyses are joined with the extant ISEE, Japan, IPS data available in near real time, supplemented by Murchison Widefield Array (MWA, western Australia) observations, thus covering different times and Earth longitudes, to input into tomographic reconstructions to visualise and track conditions throughout the inner heliosphere. Such a high number of observations offers the possibility of increasing the resolution of these tomographic reconstructions for greater accuracy in the visualisation, tracking, and resulting predictions. These reconstructions and predictions are further enhanced through use as input into an Enlil solar wind model variant under test at the Met Office.

Speaker: Richard Fallows (RAL Space - UKRI STFC)

83 SIMPL Solutions for Complex Solar Challenges: A New LOFAR Solar Imaging Pipeline

Solar radio emissions originate from a wide range of phenomena — from faint gyrosynchrotron emission associated with CMEs, to thermal emission from the quiet Sun, to intense coherent emissions from solar radio bursts. These emissions can span up to nine orders of magnitude over small spans in time and frequency, requiring spectroscopic snapshot imaging to capture their full complexity. However, calibrating solar radio data, particularly from aperture arrays with large fields of view like LOFAR, remains a major challenge. Standard calibrator sources are often dominated and are not visible in the presence of the Sun, and even stronger sources, A-team sources, are frequently contaminated by solar flux, especially during solar radio bursts.
To address these challenges, we have developed a robust, fully unsupervised solar calibration and imaging pipeline — the Solar Imaging Pipeline for LOFAR (SIMPL). This pipeline, tuned for both LBA and HBA, significantly enhances image fidelity and dynamic range (by 1–2 orders of magnitude) through several calibration and flagging strategies tailored for solar data. These include: careful selection of data to be used for calibration, a custom RFI flagger optimized for solar data, and a self-calibration scheme tuned specifically for the solar case.
We are also actively developing full-Stokes polarization calibration and imaging capabilities. This approach leverages the unpolarized sky at these low radio frequencies, which appears polarized only due to the instrumental beam effects. Although still in early stages, our preliminary results are promising, demonstrating polarization leakage levels below 0.5%.
In this presentation, I will describe how we addressed the specific challenges of solar imaging with LOFAR, the strategies implemented in SIMPL, and highlight some key science results obtained by using this pipeline.

Speaker: Soham Dey (National Centre for Radio Astrophysics)

84 Solar and Space Weather Observations with LOFAR

Over the past 20 years, low-frequency solar radio astronomy has opened a new spectral window on the Sun. Distributed array telescopes, capable of fast interferometric imaging observations and electronic pointing have completely changed the technical and scientific approaches to studying various aspects of solar and heliospheric activity at frequencies between 20 and 300 MHz. Among them, LOFAR has proven extremely powerful in terms of unparalleled resolution and sensitivity, and has enabled numerous studies and exciting discoveries about solar activity. We will review and highlight some of the recent works in solar physics and space weather making use of LOFAR observations, and outline the future directions of research of the solar radio community in the LOFAR2.0 era.

Speaker: Kamen Kozarev (Institute of Astronomy and National Astronomical Observatory, Bulgarian Academy of Sciences)

Poster flash talks

85 Calibrating LOFAR data for solar physics using a sun model

The Sun is an extended, bright and variable source. Solar radio emission of our interest is often brief and intense, with a typical duration of a few seconds and a flux exceeding $10^7$ Jy. Due to these features, one can only use the brightest calibrators during calibration and cannot benefit from a long integration time for solar observations. This talk presents a new calibration method incorporating a sun model to improve the calibration. Usually, calibration of LOFAR solar data consists of two steps: (1) calibration of the ‘quiet’ Sun without significant radio bursts using a bright calibrator (as a calibration reference); (2) transfer of solutions from the ‘quiet’ Sun to the Sun flares. The new method creates a model of the ‘quiet’ Sun during the first phase. Subsequently, the Sun model is combined with the existing calibrator model, Cassiopeia A, to calibrate the ‘quiet’ Sun. We compare the ‘quiet’ and Sun flare images based on different calibration strategies with or without the Sun model to demonstrate if there is an improvement.

Speaker: Hyoyin Gan (Leibniz Institute for Astrophysics Potsdam (AIP))

86 Interplanetary scintillation for diagnostic of the Solar Wind.

Remote diagnostic of solar wind is of utmost importance for our understanding of the space weather and its impact on space and ground technologies. With help of interplanetary scintillation (IPS) observations we are able to asses some of the parameters of the solar wind plasma. Using LOFAR radio telescope we compare and analyse couple of SW velocity estimators, which we believe can improve monitoring of SW.

Speaker: Barbara Matyjasiak (CBK PAN)

87 Galaxy detection with deep learning in radio data

Astronomical facilities generate ever-increasing data volumes, rapidly approaching the exascale. This is especially true for modern radio-interferometers for which the foreseen data rate raises strong concerns regarding the scaling capability of classical analysis methods.

In this talk, I will introduce YOLO-CIANNA (Cornu et al. 2024), a deep-learning object detector designed for astronomical images, and present how we used it to detect and characterize galaxies in simulated 2D continuum images and HI emission cubes from the first two editions of the SKAO Science Data Challenges (Bonaldi et al. 2020, Hartley et al. 2023). Thanks to this approach, we improved the SDC1-winning score by 139% and enabled team MINERVA to achieve first place in the SDC2. I will then present preliminary results from the application of our method to continuum images from LOFAR (LoTSS DR2) and HI cubes from MeerKAT (preliminary LADUMA), and discuss how we plan to generalize its application to other surveys.

Speaker: David Cornu (LUX, Observatoire de Paris)

88 Investigating Extreme Ionospheric Conditions with LOFAR: A Focus on the Mother's Day Superstorm

The May 2024 Mother’s Day superstorm, classified as a G5-level geomagnetic event, was the strongest since November 2003. While the ionospheric response to such extreme space weather is typically monitored by conventional tools like Global Navigation Satellite System (GNSS), ionosondes, and ground-based magnetometers, this study underscores the unique and pivotal contributions that LOFAR can provide to space weather investigation.

LOFAR’s dense core stations enable detection of fine-scale ionospheric disturbances (~100 meters), while its international stations can provide a broader, mid-latitude European perspective. Moreover, the system’s dual-antenna design, comprising Low Band (LBA) and High Band (HBA) antennas, supports multi-frequency observations, offering unprecedented resolution in probing ionospheric dynamics.

During the storm’s main phase, LOFAR LBA observations revealed pronounced signal fading and absorption, correlating with the dramatic equatorward expansion of the auroral oval into mid-latitude Europe. This phenomenon, indicative of enhanced ionization and D-layer absorption at lower frequencies, was simultaneously confirmed by Total Electron Content (TEC) maps from GNSS and with observed changes in ionosonde parameters such intense and blanketing E-Region echoes, primarily occurring at virtual heights between approximately 100 and 200 km, alongside substantial deflections in local geomagnetic field components registered by magnetometers.

As the storm progressed into its recovery phase, LOFAR HBA measurements captured intense scintillation events, directly attributable to the presence of fast-moving (approaching 800 m/s), small-scale ionospheric irregularities.

The application of two different techniques for velocity reconstruction, using cross-correlation of signals from different stations and Fresnel’s frequency from single stations, enabled us to pinpoint an effective altitude of these scintillating structures, revealing the presence of uplifted ionospheric features extending beyond 1500 km. Such high-altitude phenomena were undetectable by conventional high-frequency (HF) ionosondes due to severe D-layer absorption, pervasive G-conditions, or simply altitude ranges constraints.

In addition to ionospheric disturbances, LOFAR also captured a class X 3.9 solar flare and an associated solar radio burst on the morning of May 10th. Notably, post-storm ionospheric conditions on May 12, 2024, were ideal for high-quality LOFAR observations of the redshifted H-alpha spectral line, suggesting that geomagnetic activity may help predict windows of enhanced observational quality.

In conclusion, this research represents a pioneering effort in employing LOFAR's unique observational capabilities for a comprehensive investigation of the multi-scale ionospheric response during an extreme geomagnetic superstorm. By meticulously integrating LOFAR data with established space weather datasets, we not only validate LOFAR's efficacy as a powerful instrument for ionospheric research but also highlight its distinctive advantage in resolving previously unobservable storm-time ionospheric features.

Speaker: Rebecca Ghidoni (Istituto Nazionale di Geofisica e Vulcanologia)

89 Comprehensive study of type II radio bursts and the properties of the associated shock waves

Type II radio bursts are solar radio emissions associated with coronal shock waves and are believed to be produced by electrons accelerated by these shocks. As radio signatures of coronal shocks, they are typically found near the expanding edges of coronal mass ejections (CMEs), making them valuable for studying the dynamics of CME-related shocks in the solar corona. Here, we aim to determine the regions in the solar corona and their properties where the CME-driven shock waves accelerate electrons. To do this, we combine radio observations with magneto-hydrodynamic (MHD) simulations of the solar corona. We conduct an analysis of ten type II radio bursts exhibiting emissions in the 20--300 MHz frequency range from Solar Cycle 25. We used a combination of observatories to obtain images and dynamic spectra of type II radio bursts, including spectra recorded by LOFAR IDOLS for some of these events. The novelty of this study lies in the use of radio imaging data for all type II bursts considered to examine the positions of the radio sources. The radio source positions, combined with a geometrical fitting of the CME shock are used to determine essential shock parameters at the acceleration region such as the Alfvénic Mach number and shock normal angle, in the context of the MHD simulations. The shock parameters are then combined in a comprehensive statistical study with the properties of the radio emission observed, electron energies estimated from herringbone radio bursts, CME speeds in both the lateral and radial directions and the presence of open/closed magnetic field regions and other radio emissions.

Speaker: Diana Morosan (Department of Physics and Astronomy, University of Turku, 20014 Turku, Finland)

90 Observing high-latitude ionosphere at multiple scale sizes

The Kilpisjärvi Atmospheric Imaging Receiver Array (KAIRA) is an array of VHF radio antennas which is often used for radio astronomy. Located in the high arctic in Kilpisjärvi, Finland, KAIRA utilises LOFAR technology as a single station. LOFAR has been frequently used to infer properties of the ionosphere, however, the use of KAIRA to do this is much less common (Fallows et al., 2014).
Observing across multiple scale sizes in the ionosphere is not a trivial task and an extensive suite of instrumentation was needed. KAIRA is sensitive to plasma structures with spatial scales of ~100 m up to ~5 km which can cause variations in the observed signal intensity (Fallows et al., 2020). The use of KAIRA therefore provides information on the small- to medium-scale ionospheric structuring within the instrument field-of-view. Additionally, other ground-based and space-based instrumentation are used in conjunction with modelling techniques to provide wider context to the KAIRA observations. The European Incoherent SCATter (EISCAT) radars were used to observe large-scale plasma structures, such as polar cap patches and blobs, which have the ability to seed the smaller-scale structuring that would be observed by KAIRA due to instability mechanisms. Thus, the use of these radars provides context to the larger, physical mechanisms at work. The smaller-scale irregularities can then be inferred from Global Navigation Satellite System (GNSS) receivers. This is because smaller-scale irregularities are needed to cause phase and amplitude scintillation. The use of GNSS receivers in this way not only provides information on the scale sizes of the present structures but also allows for inference to be made regarding the practical, engineering applications of the research. As observation of ionospheric structuring is not currently possible with any one instrument, the Scales of Ionospheric Plasma Structuring (SIPS) experiment was conducted, providing coordinated observations of the same plasma volume using multiple instruments. The results of this experiment are discussed.
References:
Fallows RA, Coles WA, McKay-Bukowski D, Vierinen J, Virtanen II, et al. 2014. Broadband meter-wavelength observations of ionospheric scintillation. J Geophys Res Space Phys 119: 10544–10560. https://doi.org/10.1002/2014JA020406.
Fallows RA, Forte B, Astin I, Allbrook T, Arnold A, et al. 2020. A LOFAR observation of ionospheric scintillation from simultaneous medium- and large-scale travelling ionospheric disturbances. J Space Weather Space Clim 10: 10. https://doi.org/10.1051/swsc/2020010.

Speaker: Sophie Maguire (Space Environment and Radio Engineering (SERENE) research group, University of Birmingham, UK)

91 Preliminary results of observing ionosphere activity using 3C sources

To study the ionosphere using LOFAR, strong radio sources such as Cassiopeia A (Cas A) or Cygnus A (Cyg A) are typically observed. However, few studies have explored the use of other sources, such as those from the 3C catalogue, for detecting ionospheric fluctuations. In my work with the LOFAR station LV614, I have conducted approximately 100 observations targeting 3C147 and 3C295, including both daytime and nighttime sessions.

I have successfully detected ionospheric activity using both sources. These observations were carried out in parallel with simulated observations of Cas A, enabling direct comparison with traditional ionospheric studies. In addition to data collected with station LV614, I have also performed observations using other international LOFAR stations. In all cases, ionospheric scintillations were detected.

In my poster, I will present the first results from these studies, demonstrating the potential of 3C sources for ionospheric research.

Speaker: Jānis Šteinbergs

92 The solar radio bursts observations with LOFAR Baldy station and two CALLISTO spectrometers

We present first simultaneous observations of the different types of the solar radio bursts made with LOFAR Baldy station and CALLISTO spectrometers located in Baldy (Poland) and Neustrelitz (Germany). The CALLISTO spectrometer (Compound Astronomical Low frequency Low cost Instrument for Spectroscopy and Transportable Observatory) is a programmable heterodyne receiver operating in the 10-80 MHz frequency range and capable of recording two polarizations. In this study, we present a preliminary analysis of dynamic spectra of different types of solar radio bursts. We examine their general characteristics, with particular emphasis on similarities of dynamic spectra obtained by LOFAR and CALLISTO, as well as the velocities of electron beams responsible for bursts generation. In addition to LOFAR and CALLISTO observations, we present the data recorded by the GOES satellite in X-ray range. Our results demonstrate that observations made by both types of spectrometers, in combination with observations in X range, provide better understanding of the physical processes responsible for solar radio bursts generations.

Speaker: Dr Bartosz Dabrowski (Space Radio-Diagnostics Research Centre, University of Warmia and Mazury in Olsztyn)

93 Magnetic Field Geometry and Anisotropic Scattering Effects on Solar Radio Burst Observations

Sub-second fine structures of solar radio bursts reveal complex dynamics in the corona, yet their observed features are additionally complicated by radio-wave scattering in the turbulent corona. LOFAR imaging of individual fine structures during a single event revealed puzzling, non-radial motions of apparent sources at superluminal speeds and rapid expansion on millisecond timescales. We examine how anisotropic turbulence and non-radial magnetic field structures shape the morphology, timing, and source positions of these fine structures using radio-wave propagation simulations. We find that apparent source motion follows magnetic field lines rather than the density gradient, and that the major axis of the scattered source is perpendicular to the local field. Using a dipolar magnetic field model of an active region, we reproduce the observed source motion parallel to the solar limb, providing a natural explanation for the LOFAR observations. The observed fine structure drift-rate is also influenced by the source location within the field structure, due to variations in temporal broadening. Strong anisotropy aligned with a dipolar magnetic field causes the apparent-source images to bifurcate into two distinct components, with characteristic sizes smaller than in unmagnetized media. The findings underscore the role of magnetic field geometry and anisotropic scattering for the interpretation of solar radio bursts and highlight that anisotropic scattering produces more than a single source.

Speaker: Daniel Clarkson (University of Glasgow)

94 Exploring the LOFAR properties of the CARMENES M-dwarf star systems

The CARMENES high-resolution spectrograph located at the 3.5m Calar Alto telescope, which provides simultaneous coverage at 0.52-1.71 micrometers, is a powerful instrument for the study of nearby M-dwarf stars. It has been central to a monitoring campaign of more than 2200 such objects, complementing its excellent infrared coverage with information from other bands ranging from the optical to the X-rays, allowing for exquisite constraints on key physical parameters linked to either stellar activity or exoplanetary properties (e.g. rotation and orbital periods, masses, etc). In this work, we explore the properties of CARMENES objects in the radio bands at 144 MHz and 1.4 GHz with LoTSS-DR3 and VLASS, surveys which cover the full Northern sky, to explore the persistent radio emission of these objects. Such persistent emission may arise from either the stellar physics of M-dwarf (which are small and compact, with masses between 0.08 and 1 solar masses, and thus feature very strong and stable magnetic fields ranging from hundreds to thousands of Gauss), or trace the star-planet interactions predicted for exoplanetary systems with magnetospheres. This work complements the wider community's search for transient signals associated to star-planet emission by attempting to find correlations between known CARMENES properties and either burst or sustained radio emission from these objects at 21cm and low radio frequencies.

Speaker: Etienne Bonnassieux (IAA-CSIC)

95 Investigating double bump air showers

Double-bump showers are a rare class of extensive air showers (EAS) predicted by Monte Carlo simulations. They occur when a high-energy secondary particle, the leading particle, travels significantly farther than the rest, creating a distinct double-peaked longitudinal profile. So far, no experiment has been able to directly detect these showers. The unique radio footprint of double-bump showers, characterized by multiple Cherenkov rings, provides a way to reconstruct longitudinal profiles from radio observations. For this reconstruction it is crucial to observe the radio signal over a broad frequency range, which will be possible with the LOFAR 2.0 and later SKA. This offers a new opportunity to probe hadronic interactions and constrain particle cross sections at ultra-high energies.

In our analysis, we simulate the EAS using CORSIKA with the CoREAS plugin for radio.
We developed a new method based on the Akaike information criterion to identify double bump showers in simulations by analyzing their longitudinal profiles.
Then we investigate the prevalence of these double bump showers across different cosmic ray primary particles and various hadronic interaction models.
We create a skeleton of the EAS which consists of all the particles with at least $1\%$ of the primary energy, allowing us to confirm the leading particle hypophysis and and track shower development following these particles. This will enable us to relate the attributes of the leading particle to measurable parameters.
Depending on the exact shower properties, the radio footprint of a double bump shower can create a complex interference pattern, consisting of multiple rings. From this information, the longitudinal profiles can be extracted.

Speaker: Prof. Stijn Buitink (VUB)

96 Correlation between diffuse gas phases and Faraday tomographic data : a numerical point of view

Observations of diffuse interstellar polarization at meter wavelengths reveal intricate Faraday depth structures, likely tracing interactions between magnetized plasma and neutral gas. A strong correlation with CNM filaments has been proposed, but not reproduced in simulations with low CNM fractions, suggesting the CNM content may shape Faraday structures.

We investigate whether the CNM fraction drives the correlation between Faraday structures and HI brightness temperature, as observed in the 3C196 field. Using numerical simulations with varying CNM content, we test the role of cold gas in coupling neutral structures to magnetized plasma, and assess the influence of turbulence and magnetic field topology.

We analyze 14 three-dimensional magnetohydrodynamic (MHD) simulations of Fourier-driven turbulence in 50 pc cubes, post-processed with the MOOSE code to generate synthetic synchrotron polarization and Faraday tomography. We compute spatial correlations between Faraday depth structures and phase-separated HI brightness temperature using the Histogram of Oriented Gradients (HOG) method and compare results with LOFAR observations, including instrumental effects.

The correlation strength depends primarily on magnetic field orientation and turbulence, not solely on CNM abundance. When the mean field is aligned with the line of sight, the WNM dominates the correlation, even at high CNM fractions. In the perpendicular case, the correlation weakens for all phases. Noise affects the phases differently and modulates the correlation amplitude.
None of the simulations fully reproduces the observed dominance of CNM in 3C196.

Our results show that CNM fraction alone is insufficient to explain the correlation with Faraday structures. Turbulence,
magnetic field dynamics, and topology are also key factors, highlighting the need for a comprehensive approach to understanding the
coupling between neutral gas and magnetized plasma in the diffuse ISM.

Speaker: Jack Berat (LPENS)

97 Ionospheric and solar activity constraints on LOFAR observation scheduling

I will present the initial results and planning on implementing constraints for LOFAR observation scheduling. These constraints are based on the metrics for the state of the ionosphere as well as solar activity (and radio emission) derived from dedicated monitoring. LOFAR station data reduction and the corresponding metrics will be discussed, as well the plans for their integration into the telescope monitoring and scheduling system (TMSS).

I will also discuss the benefits of this approach for telescope operations and the data quality monitoring shared with users.

Speaker: Aleksandar Shulevski

98 Characterising the Sensitivity Pattern of the Irish LOFAR Station (IE613) using Pulsar Observations

The LOw Frequency Array (LOFAR) is a hierarchical array of dipole and bowtie antennas, distributed across Europe. The Irish LOFAR station (IE613) is located at Birr Castle, Co. Offaly. As one of the 14 international stations, it comprises a set of Low Band Antennas (LBA) and 96 High Band Antennas (HBA) tiles. The response of a single station is trivial and different works have been carried out in the past. Several factors contribute to the overall performance of the system, among them the effective collecting area, beam model, contamination due to radio frequency interferences (RFI), system noise and turbulent effects in the ionosphere (e.g. Kondratiev et al., 2016 ). As a ’software telescope’, LOFAR is particularly sensitive to signal corruption from both direction-independent and direction-dependent effects, which influence the observed radio waves as they travel from the source to the observer. In this regard, Radio Interferometer Measurement Equation (RIME), as extension of the fundamental van Cittert-zernike theorem, is employed in data calibration (e.g. Kansabanik et al., 2025, Creaner & Carozzi, 2019, Murley et a;., 2019, Price & Smirnov, 2015, Tasse et al., 2012, Smirnov et al. (I),(II),(III),(IV), 2011, Nijboer & Noordam, 2007, Sault et al., 1996 ). This mathematical framework implements correction factors in form of elements of Jones 2x2 matrices (or Mueller 4x4 matrices). Taking into account its complexity, the response of individual LOFAR stations has been extensively studied (e.g. McKenna et al., 2024, Blaszkiewicz et al., 2018, Kondratiev et al., 2016, Bilous et al., 2016, Noustsos et al., 2015 ). In this study, we present an analysis of the HBA response of the Irish station (IE613) by tracking 11 pulsars across the sky. We investigate how the signal-to-noise ratio (S/N) varies as each pulsar rises, culminates, and sets, thereby constructing a sensitivity map of the station’s beam pattern.

Speaker: Letizia Vincetti (Trinity College Dublin (TCD) - School of Physics)

99 A study of the diffuse emission of the Fan region with QUIJOTE experiment

Microwave and radio observations exhibit some interesting features in the Galactic plane. One of those is the Fan region which is an extended region located in the Perseus arm at a distance of 500 pc. Fan region has highly polarized emission from several MHz up to 353 GHz, which is ascribed to synchrotron but nowadays is largely unexplained. Here we present new measurements in intensity and in polarization at the microwave frequencies 10-20 GHz coming from the Multi Frequency Instrument (MFI) of the Q-U-I-JOint Tenerife Experiment (QUIJOTE). From these new maps, we present a characterizarion of the synchrotron emission and the magnetic fields.

Speaker: Beatriz Ruiz-Granados (Universidad de Córdoba)

100 LOFAR Ionospheric Research Group: Advancing Ionospheric Science with LOFAR

The Earth's ionosphere significantly influences low-frequency radio wave propagation, introducing distortions that challenge the precision of radio astronomical observations. The LOFAR Ionospheric Research Group (LIRG) leverages the unique capabilities of the LOw Frequency ARray (LOFAR) to study these ionospheric effects. LIRG fosters collaboration between ionospheric scientists and radio astronomers to investigate plasma velocities, ionospheric scintillations, and Traveling Ionospheric Disturbances (TIDs), modelling atmospheric impacts and analysing extreme space weather events. Single-station studies further provide localised insights into ionospheric variability. LIRG's work extends to improving LOFAR's observational strategies through dynamic scheduling based on ionospheric conditions and advancing calibration techniques, such as Direction, Time, Amplitude, and Phase Calibration (DTAC), using bright extragalactic radio sources (3C sources) to probe ionospheric variations. These efforts primarily advance ionospheric research by harnessing LOFAR's capabilities while improving its astronomical data quality. LIRG strengthens LOFAR's role as a vital tool for studying the ionosphere and a powerful radio telescope, setting the stage for next-generation low-frequency arrays such as the SKA.

Speaker: Dorota Przepiórka-Skup (Centrum Badań Kosmicznych Polskiej Akademii Nauk)

101 Imaging uncalibrated LOFAR data for real-time transient hunts

In recent years, a new class of radio transients has emerged: Long Period Transients (LPTs). These radio transients have unexpectedly long periods of minutes to hours, with burst durations of seconds to minutes. In this project, we have developed a new method of analysing data from LOFAR to detect radio transients on intermediate timecales (seconds to minutes) in real time. It has been tested on 27 observations from the LoTSS survey and will in the future perform real time analysis of commensal LOFAR data using the Euroflash cluster. In order to achieve transient searches in real time, no calibration and no cleaning is performed on the data. A transient search is performed in the image plane on difference images (the residual of subtracted consecutive images) on timescales of 8, 16, 32 and 64 seconds. Filtering algorithms are used to discern artefacts / false positives from possible transients.

Speaker: Lars Zwaan (University of Amsterdam)

102 Investigation on resonant plasma structures and their role on ionospheric radio diagnostics by using LOFAR and GNSS Data and Modelling

Radio diagnostics of the ionosphere based on measurements using LOFAR and GNSS and their combination, and using data from ionosondes, satellites, incoherent scatter radar, etc. is being used to solve a number of practical (such as ultra-high-precision positioning) and fundamental problems in the physics of ionospheric plasma and coupling in the system Sun-Solar Wind (SSW)-Lithosphere (Earth)-Atmosphere-Ionosphere-Magnetosphere (LEAIM).
(1) We present the results of modelling and comparison with available experimental data on the following aspects of coupling in the LEAIM system and Structures in the Ionospheric Plasma. (i) A linear model of excitation of resonant wave train (RWT) of Atmospheric Gravity Waves (AGW) by the solar terminator is constructed. The main characteristics (wavelength, effective velocity and period) of long-period (about 1 hour) gravity waves correspond to GNSS observations. It is shown that the actual spatial periods determined on the basis of RWT maxima and minima differ by tens of percent, and their values correspond to those determined using GNSS data. The corresponding short-period (of the order of a few mins.) periods were detected on the basis of LOFAR data, with high-frequency electromagnetic wave (HFEMW) emission from Cassiopeia supernova remnant. (ii) Models of resonant ionospheric disturbances/TID, detected using satellite and LOFAR data, are currently being developed. The resonant disturbances in question may be associated with AGW resonators and waveguides present at various altitudes in the atmosphere-ionosphere, as well as with the presence of shear wind in the E and F regions of the ionosphere (in the thermosphere). According to our assumption, the corresponding ionospheric disturbances with periods of the order of the Brunt-Väisälä period are observed by LOFAR, with HFEMW radiation from pulsars.
(2) A fundamental task of ionospheric physics is also to determine the mechanisms that limit the amplitudes of the above-mentioned resonant disturbances. A model for AGW excitation is currently being developed taking into account nonlinear losses that determine amplitude saturation.
(3) Analytical relationships have been obtained that describe the dynamics of the Perkins instability in plasma in the 2.5+1-dimensional approximation (taking into account the integration of the corresponding equations along the direction of the geomagnetic field) and in the presence of AGW. A corresponding numerical model is under development. Test numerical results for the disturbances of the plasma ionospheric layer Es under the influence of the propagating AGW are obtained.
Possible applications of the obtained results and the corresponding prospects for radio diagnostics of ionospheric space weather are discussed.

Speaker: Leszek Błaszkiewicz (Space Radio-Diagnostics Research Centre, UWM Olsztyn)

103 Towards the first LoTSS catalog of diffuse cluster radio sources with machine learning

The advent of next-generation radio surveys, such as those conducted with LOFAR, ASKAP, and the upcoming SKA, is expected to revolutionise our understanding of the radio universe. However, the vast volume and complexity of data generated by these instruments present significant challenges for traditional manual cataloguing and data analysis techniques. To fully exploit these datasets, the integration of artificial intelligence and the use of high-performance computing infrastructures is essential.

While machine learning has already been applied to the detection of compact objects and radio galaxies, detecting diffuse radio sources, such as radio halos and relics in galaxy clusters, remains a critical challenge. Conventional approaches often involve computationally expensive pre-processing steps, such as the subtraction of compact sources prior to detecting diffuse emission, an increasingly impractical task as dataset sizes continue to grow. To address these issues, we employ Radio-UNet, a fully convolutional neural network based on the U-Net architecture, designed to enhance the automated identification of diffuse radio sources in galaxy clusters. Trained on synthetic radio observations derived from cosmological simulations, our model was validated on diffuse emission in galaxy clusters observed by the LOFAR Two-Metre Sky Survey (LoTSS). Furthermore, our network has proven to surpass human capability, facilitating the discovery of diffuse radio emission in a particular galaxy cluster where an unprecedentedly large-scale radio structure was detected and studied in detail. In this talk, I will present the achieved results (Stuardi et al., 2024, 2025) and showcase the ongoing effort to apply this network to the LoTSS dr3, creating the largest catalogue of clusters with diffuse radio emission to date.

Speaker: Chiara Stuardi (IRA INAF)

16:20 Poster viewing + coffee / tea break

Science talks

104 Periodic changes in the dynamic spectra of pulsars as an effect of signal propagation through the ionosphere

For the long-wave radio spectrum in which LOFAR operates, the ionosphere is of key importance in the context of radiation transfer and is a source of distortion in the recorded signal. Therefore, good knowledge and predictability related to the shape and dynamics of the ionosphere is extremely important for the LOFAR system [1].
However, for astrophysical research it is a disadvantage, it can provide an additional and independent source of information from standard techniques (like GNSS) in the processes of studying and modelling the ionosphere. Furthermore, the remarkable sensitivity of the LOFAR system makes it an extremely sensitive tool for observing flux changes in scintillation processes in the ionosphere. This is exploited by observing bright sources such as CasA or CygA. See for example [2]. At the same time, LOFAR is a powerful instrument for radio diagnostics of ionospheric plasma.
Observations of pulsars carried out since the very beginning of the LOFAR Radio Telescope prove that it is one of the best instruments for this type of research (see, for example, [3]). However, most of the analysis is based on data obtained at significant integration times. In a previous paper [4], we showed the qualitative influence of the ionosphere on changes in the relative flux of pulsar profiles. The present work, based on the dynamical spectra of bright pulsars, highlights in many cases an unusual variability that may be – as we assume – caused by the ionosphere. Moreover, this variability is well explained by models of fine-scale variations in the ionosphere.
In our studies, dynamic spectra are constructed based on temporal S/N (signal-to-noise) values. The analysis of variability based on wavelet analysis, the study of the second-order spectrum and the comparative analysis of such a signal with the results of measurements based on GNSS data allow us to determine the dynamics of changes in the direction of the observed source. Additional aspect is the determination of the PSI - Pulsar Scintillation Index, based on the S4 index described in [5,6].
During the presentation, we will show the observed phenomena and the presence of quasi-periodic variations visible in the dynamical spectra. We will discuss the possible correspondence between the characteristics of observed spectra revealed from LOFAR data and theoretical characteristics of wave excitations in the atmosphere-ionosphere. We will also present the results of correlations between the dynamical spectra of selected pulsars observed simultaneously by the Polish LOFAR stations PL612 and PL611.
References:
1.M. P. van Haarlem et al., “LOFAR: The LOw-Frequency ARray,” A&A, 556 ,2013, A2, DOI: https://doi.org/10.1051/0004-6361/201220873
2. R. A. Fallows et al., “Broadband meter-wavelength observations of ionospheric scintillation”, J. Geophys. Res. SpacePhysics,119, 10,544–10,560, 2014 doi:10.1002/2014JA020406.
3. A. Noutsos et al., 2015 Pulsar polarisation below 200 MHz: Average profiles and propagation effects, A&A, 576, A62, 2015 DOI: 10.1051/0004-6361/201425186.
4. L.P. Błaszkiewicz et al., “Finding the Ionospheric Fluctuations Reflection in the Pulsar Signals’ Characteristics Observed with LOFAR”. Sensors.; 21(1):51, 2021, DOI: https://doi.org/10.3390/s21010051.
5. B. Forte et al., Interpretation of Radio Wave Scintillation Observed through LOFAR Radio Telescopes, Astroph. Journal, Supplement Series, Vol. 263, Issue 21, 2022, DOI: 10.3847/1538-4365/ac6deb
6. P. Flisek et al., "Towards the possibility to combine LOFAR and GNSS measurements to sense ionospheric irregularities", J. Space Weather Space Clim. Vol. 13, 2023, DOI: https://doi.org/10.1051/swsc/2023021

Speaker: Leszek Błaszkiewicz (Space Radio-Diagnostics Research Centre, UWM Olsztyn)

105 Monitoring horizontal electron density gradient with LOFAR PL610 in single station mode

LOFAR (LOw Frequency ARray) radio telescope network enables high-resolution interferometric observations in the frequency range of 10 – 240 MHz. It can be used as a distributed array, but utilising a single LOFAR station can also provide valuable information. The cross-correlation data enable sky imaging at selected frequencies, with a time resolution of 1 second. Such mapping can be used for monitoring the apparent position of the strongest radio sources over time. 

The position variability at low radio frequencies depends on the ionospheric conditions. Total Electron Content (TEC) along the line of sight, especially horizontal gradients in TEC, can impact systematic shifts in the apparent radio source position. The temporal evolution of its shift can be used to observe the structures in the ionosphere. 

The LOFAR PL610 station in Borówiec, Poland, was used to conduct continuous observations of the strongest group of radio sources (the A-Team: CasA, CygA, TauA, and VirA) for over two years. The available data are recorded in local time, allowing monitoring of diurnal ionospheric variability, as well as observations of space weather events.

In the following study, we present the standard patterns related to the diurnal ionospheric cycle, including build-up and decay of ionospheric gradients during the day. Moreover, we show the ionospheric disturbances triggered by geomagnetic storms. The analysis provides insight into the dynamics of the ionosphere in the mid-latitude geomagnetic region, utilising the LOFAR PL610 station as a tool for monitoring the ionospheric region that cannot be monitored so efficiently with GNSS methods.

Speaker: Mariusz Pozoga (Space Research Centre PAS)

106 Combination of LOFAR and GNSS observations for a statistical characterisation of ionospheric irregularities

The Earth’s ionosphere originates propagation effects at various orders that can be observed on radio waves that traverse it. Ionospheric propagation effects can be utilized to infer properties of the ionosphere: for example, temporal fluctuations in the received radio-wave intensity (or scintillation) can be associated with irregularities forming in the inertial subrange of the spatial distribution of electron density structures.

The observation of different propagation effects (e.g., on the phase and on the intensity of radio waves) can be utilized to understand the spatial scales over which electron density irregularities form and evolve. This is instrumental to the understanding of instability mechanisms taking place in the ionosphere. Due to the dispersion nature of the ionospheric plasma, the observation of these propagation effects over a wide interval of radio wave frequencies allows to sample ionospheric irregularities over a wide range of spatial scales.

This contribution discusses the combination of ionospheric observations carried out by means of Global Navigation Satellite Systems (GNSS) and by means of LOFAR radio telescopes. Whilst GNSS observations focus more on phase fluctuations, LOFAR observations are for radio wave scintillation at VHF (from sources such as Cas A or Cyg A). An essential aspect in this combination is the different sensitivity of the two instruments to ionospheric propagation effects and, hence, to the ability of detecting ionospheric structures.

Here, a characterization of different types of ionospheric irregularities in relation to the propagation effects that they induce as well as to the sensitivity of the two instruments is discussed, together with a discussion on the potential offered by this type of studies for future ionospheric radio science.

Speaker: Biagio Forte (University of Bath)

107 Dynamic Ionospheric Notifications for Operations and Scheduling (DINOS): Using Ionospheric Observations to Support LOFAR2.0 Operations

The Low Frequency Array (LOFAR) is one of the most advanced radio telescopes in the world. When radio waves from a distant astronomical source traverse the ionosphere, structures in this plasma affect the signal. The high temporal resolution available (~10 ms), the range of frequencies observed (10-90 MHz & 110-250 MHz) and the large number of receiving stations (currently 52 across Europe) mean that LOFAR can also observe the effects of the midlatitude and sub-auroral ionosphere at an unprecedented level of detail.
Case studies have shown substructure within a sporadic-E layer (Wood et al., 2024), substructure within a Medium Scale Travelling Ionospheric Disturbance (TID) (Dorrian et al., 2023), a Small Scale TID (Boyde et al., 2022) and symmetric quasi-periodic scintillations (Trigg et al., 2024). The small-scale size of many of these features (kilometres to tens of kilometres) implies a local source. A climatology of observations during daylit hours shows that ionospheric waves primarily propagate in the opposite direction to the prevailing wind, suggesting that the structures observed are the ionospheric manifestation of quasi-upward propagating Atmospheric Gravity Waves (AGWs; Boyde et al., 2025). A statistical study (manuscript in preparation) shows that there is a statistically significant link between ionospheric structures observed by LOFAR and lightning activity, with a lag of two hours.
The Dynamic Ionospheric Notifications for Operations and Scheduling project is using ionospheric results to attempt to mitigate the ionospheric effects on LOFAR observations. A database of 2,911 hours of observations is used to determine the quality of the radio astronomy observations on these occasions. The ionospheric conditions associated with these observations are established, using different approaches with different instruments. These approaches include using ionosondes, magnetometers and HF Continuous Doppler Sounding Systems. Different approaches provide information on different scales of plasma density variations. The suitability of these approaches to forecast when ionospheric conditions will be appropriate for low-frequency radio astronomy is determined. Such a forecast could reduce the number of observations which later need to be discarded due to the ionospheric conditions, optimizing the usage of telescope time, and making the operations more sustainable by reducing the computational and storage resources required. These methods could also predict when the ionosphere will be extremely depleted, enabling observations at lower frequencies than have been routinely possible to date.
References
Boyde, B. et al. (2025). Statistics of Travelling Ionospheric Disturbances Observed Using the LOFAR Radio Telescope. J. Space Weather Space Clim., 14, doi:10.1051/swsc/2025002
Boyde, B. et al. (2022). Lensing from small-scale travelling ionospheric disturbances observed using LOFAR, J. Space Weather Space Clim., 12, 34. doi:10.1051/swsc/2022030
Dorrian, G. D. et al. (2023). LOFAR observations of substructure within a traveling ionospheric disturbance at mid-latitude, Space Weather, 21, 2022SW003198. doi:10.1029/2022SW003198
Trigg, H. et al. (2024). Observations of high definition symmetric quasi-periodic scintillations in the mid-latitude ionosphere with LOFAR. J. Geophys. Res., 2023JA032336. doi:10.1029/2023JA032336
Wood, A. G. et al. (2024). Quasi-stationary substructure within a sporadic E layer observed by the Low Frequency Array (LOFAR), J. Space Weather Space Clim. 14, 27. doi:10.1051/swsc/2024024

Speaker: Alan Wood (University of Birmingham)

Friday 26 September

Science talks

108 Overview of advancements in understanding lightning initiation and propagation with LOFAR

LOFAR is the most sensitive and precise lightning interferometer currently operational. The LOFAR lightning research group has been using this capability to unveil lightning plasma physics that is impossible to explore in any other way. In particular, the lightning group has made significant progress in imaging and understanding lightning initiation, propagation, cloud-top discharges, thunderstorm charging, and many other phenomena.

During lightning plasma channel (called leaders) propagation LOFAR observes a series of extremely fast streamer bursts that are too fast to temporally resolve with any other instrument. Each streamer burst propagates around 1x10^5 m/s over tens to hundreds of meters, and then thermalizes to produce the next section of hot leader channel. This process shares many similarities with what LOFAR observes during lightning initiation, which is likely also a burst of streamers. The similarities and differences between these two processes are guiding our understand in how streamers interact to create lightning processes.

Thunderstorms are known to produce relatively small discharges near the top of the tropopause, which are regularly seen from space-based observations as point-like flashes of light. LOFAR has also observed these cloud-top discharges in the Netherlands, able to resolve their structure, and has reviled that they are not one single type of discharge but a wide collection of different phenomena.

Finally, it has become clear in recent years that lightning flashes in the Netherlands are upside-down relative to most lightning flashes observed elsewhere. Thus, the lightning group used the radio-emission from cosmic ray air showers during thunderstorms to reconstruct the charge distribution. The result is that Dutch thunderstorms have a charge distribution that is upside-down relative to thunderstorms in other parts of the world. Precisely why this is the case is still being explored.

In this talk we will give an overview of a few of these recent advancements in lightning science being made with LOFAR with particular attention to the new plasma physics being discovered. The talk will conclude with a discussion of the new lightning science the LOFAR2.0 will enable

Speaker: Brian Hare (ASTRON)

109 New Insights into the Nature of Lightning Intiation via LOFAR Beamforming and ATRI-D

How lightning starts is still an open question in the field of lightning physics. The in-situ electric fields observed within thunderstorms from decades of balloon measurements are far too low for both the breakdown of virgin air or what is known as the the streamer-to-leader transition. Past observations have implicated fast breakdown (FB) as a method by which lightning does initiate, however this is only witnessed in a subset of the particularity powerful thunderstorms. LOFAR has uncovered two new initiation mechanisms, one that shares similar features with FB and a second dubbed ultra-slow-propagation that is totally new and unexpected. The events that share features with FB have compatible e-folding lengths to previous observations, but very wildly in length, duration, and altitude at which they take place. Additionally, these discharges have a exponential growth in intensity. This is suggestive of a similar mechanism to FB, however, what is especially surprising is that in spite of their varying properties they all have a speed of roughly of 5.0 * 10^6 m/s. This suggests a steady state process, which is not typically seen as compatible with exponential growth. Ultra slowly propagating discharges contain bursts which individually propagate at speeds on the order of 10^6 m/s for up to a millisecond, but collectively these bursts follow a trajectory which only travels speeds on the order of 1-10 km/s. Furthermore, these bursts tend to repeat on timescales of 4 us, but also have periods of inactivity of tens to hundreds of milliseconds while still happening within the same region of space when activity is again visible.
Within this work we will present updated results on observations of lightning initiation, which is in part due to the recent refinement of the LOFAR lightning beamforming into the Adaptive Time Resolved Interferometric 3D (ATRI-D) imager. These techniques, developed by the LOFAR lightning group, leverage the dual polarity of the Low-Band Antennas (LBA) to produce observations with enhanced detail of initiation events as seen by the LOFAR array, and as such provide further clues on precisely how lightning starts. These refinements provide a means to test previously developed hypotheses of lightning initiation. LOFAR, due to its long baselines, high timing precision, and large number of antennas, has immense capability and potential as an instrument for studying lightning initiation, and as such is currently the best instrument in the world for these reasons.

Speaker: Dr Christopher Sterpka (Netherlands Institute for Radio Astronomy (ASTRON), Dwingeloo, The Netherlands)

110 Investigating the origins of three acceleration episodes during a weak solar eruption accompanied by type II radio bursts

Observing the Sun in the radio domain is a powerful tool to detect and study the presence of shock waves in the solar corona, especially in the absence of other clear observations of coronal mass ejections (CMEs) capable of driving these shocks. Electrons accelerated by coronal shocks can be remotely detected through the radio waves that they emit in the form of type II solar radio bursts. In this study, we investigate the source locations of three type II bursts using imaging and spectroscopic observations with the Low Frequency Array (LOFAR). The type II bursts occur in the absence of a notable CME, with only a faint and narrow eruption observed at other wavelengths. The type II bursts, however, indicate the presence of a shock wave and multiple periods of electron acceleration despite the presence of a weak CME. By tracking the spatial and temporal evolution of the type II radio sources over multiple frequencies, we find that the three type II bursts are generated in separate and distinct regions. We also extend the analysis into three dimensions by combining LOFAR imaging with a magnetohydrodynamic (MHD) model of the solar corona to investigate the properties of the emission regions of these type II bursts.

Speaker: Sanna Normo (Department of Physics and Astronomy, University of Turku, 20014 Turku, Finland)

111 Comparative analysis of solar activity

Detailed interferometric radio observations of solar activity allow us to constrain the dynamics of high-energy electron beams accelerated in flares and coronal mass ejections (CME), and thus to better model and study space weather effects. We report here a comparative analysis of two similar solar activity periods observed by LOFAR LBA on September 24 and 28, 2023. Both events exhibited the same radio burst sequence: an episode of strong type III bursts followed several minutes later by a type II burst in metric wavelengths, drifting between 80-20 MHz frequency. To understand these events comprehensively, we combined LOFAR observations with optical and EUV data. We employ a novel approach to processing 1-second time resolution LOFAR solar interferometry, and apply a new method for automated source extraction and measurement. During both eruptive events we observe distinct active emission regions in the solar corona, which correspond to the radio bursts and electron beams detected in situ (for the September 24 events). We investigate the dynamics of the type II solar radio sources from LOFAR interferometry for both September 24 and 28 events to understand the common physical processes underlying this type III – type II burst sequence.

Speaker: Kamen Kozarev (Institute of Astronomy and National Astronomical Observatory, Bulgarian Academy of Sciences)

112 RISER – Using LOFAR to Track Space Weather Through the Heliosphere-Magnetosphere-Ionosphere System

The UK’s NERC-funded Radio Investigations for Space Environment Research (RISER) project addresses the chain of events through which the Sun creates adverse space-weather conditions at Earth and within the Earth’s space environment. RISER aims to investigate how the LOw Frequency ARray (LOFAR) can be utilised for continuous and accurate tracking of inner-heliospheric and ionospheric plasma structures, combined with magnetospheric modelling, leading to more-precise and advanced forecasts of space-weather conditions and their impacts at Earth. RISER will provide a comprehensive understanding of the Earth’s space-environment through the use of novel radio observations and modelling techniques to investigate coupling between solar-driven inner-heliospheric structures and the Earth.

RISER is a £3.7M (FEC) NERC-funded Large Environment 5-Year Project addressing the full chain of space weather phenomena from the Sun to the Earth. RISER commenced on 1st September 2023 and will nominally run for five years across a UK-USA collaboration.

Initially focussing on a number of case studies from previous LOFAR space weather observing campaigns, the RISER project demonstrates the added value that LOFAR observations provide, from observations of interplanetary scintillation (IPS) across the inner heliosphere to observations of ionospheric scintillation and refractive effects. A vital component of the RISER project is to also model the crucial link from heliospheric conditions at Earth to conditions in the ionosphere via magnetospheric modelling. Furthermore, RISER will facilitate the upgrading of the LOFAR-UK Rawlings Array at Chilbolton to the new dual-beam, LOFAR For Space Weather (LOFAR4SW) capability, providing the potential for 24/7 space weather observations. In this presentation we will summarise the planning and work undertaken over the first two years of the project.

Speaker: Mario Bisi (UKRI STFC RAL Space)

113 Radio eyes for the Sun, Heliosphere and Ionosphere: Status and plans for the LOFAR2.0 era.

The Low-Frequency Array (LOFAR) has established itself as a formidable instrument in the field of solar physics and space weather, providing a unique vantage point for observing the Sun, heliosphere, and ionosphere. As we transition into the LOFAR 2.0 era, this presentation outlines the current status and future plans for leveraging LOFAR's capabilities, and the LOFAR IDOLS (Incremental Development of LOFAR Space-weather) project.
LOFAR's current work in solar physics involves high-resolution imaging and dynamic spectral analysis, enabling detailed observations of solar radio bursts and other coronal heliosphere and ionosphere phenomena. These observations are critical for understanding the mechanisms behind solar activity and improving our predictive models of space weather events. The LOFAR IDOLS station, a dedicated space-weather station, has been instrumental in advancing this work. It currently provides continuous monitoring of the ionosphere and Sun, tracking disturbances that can affect space weather on Earth, but also the astronomical observations of LOFAR itself.
The LOFAR2.0 upgrade promises to enhance these capabilities significantly. Plans include improving the sensitivity and spatial resolution of the array, and the simultaneous observations in LBA and HBA, which will allow for even more precise and broad imaging and tracking of solar phenomena. This will enable researchers to understand the fine structures within the solar corona and track the development of space weather events with greater accuracy.
In conclusion, the LOFAR2.0 era opens a new opportunity for solar and space weather research. With the ongoing work and future plans for the LOFAR IDOLS station and LOFAR2.0 observations, we are preparing to gain deeper insights into the Sun's influence on our space environment and to develop more robust forecasting capabilities for space weather phenomena.

Speaker: Pietro Zucca (ASTRON - Netherlands Institute for radio astronomy)

114 The detection of circularly polarized radio bursts from stellar and exoplanetary systems

In the solar system low frequency radio emission at frequencies ~200 MHz is produced by acceleration processes in the Sun and in planets’ magnetospheres. Such emission has been actively searched for in other stellar systems, as it would potentially enable the study of the interactions between stars and their exoplanets’ magnetospheres. Here we present a method meant to measure the flux density variability in an arbitrary number of directions from interferometric datasets. We implemented a multiplexed version of it to synthesize ∼ 200, 000 dynamic spectra of stars and exoplanetary systems from a ∼12,000 hours long, LoTSS dataset at ∼ 150 MHz. This additional diagnostic shows that 17 of the 134 (12.7%) targets previously identified in the LOFAR polarized images also show significant variability on few hours scale. The improved instantaneous sensitivity also lead to the detection of a rapidly drifting burst (Callingham et al. submitted) and 7 bursts from low-mass stars that vary on ∼ 0.5 − 1 hour scale, two of which hosting exoplanets. We argue that the strongly polarized structures in some of these dynamic spectra could originate from Electron Maser Cyclotron driven by star-planet interaction. I will give an update on the available software and future plans. Our results prefigure the larger populations of events that will be detectable by LOFAR 2.0 and the Square Kilometer Array (SKA), enabling detailed quantitative studies of stellar plasma environments and star-exoplanet interactions.

Speaker: Cyril Tasse (Observatoire de Paris)

10:45 Coffee / tea break

Science talks

115 Stars at low frequencies

A key question in astronomy is whether there are habitable planets around other stars. Exoplanet habitability is largely determined by the stellar environment, with stellar eruptions buffeting exoplanets while the stellar wind slowly erodes the upper layers of the atmosphere. Traditional methods struggle to directly measure the stellar environment, in particular for low-mass stars. However, by detecting radio emission from a star, we can directly measure the magnetic field strength or the plasma density in the system, providing a unique window into the conditions around these stars. In this talk, I will present an overview of the recent results in the field of low-frequency stellar radio astronomy, with a focus on LOFAR imaging surveys.

Speaker: Sanne Bloot (ASTRON, Kapteyn Astronomical Institute)

116 Spectral cutoff and periodic signal from a radio brown dwarf binary

Brown dwarfs display Jupiter-like auroral phenomena such as coherent radio emission, which is a probe of magnetospheric acceleration mechanisms and allows us to directly measure the emitter’s magnetic field strength. Radio observations of the coldest brown dwarf are particularly interesting since their magnetospheric phenomena may be very similar to those in gas-giant exoplanets. Here we study J1019, a radio-bright brown dwarf binary (T5.5+T7). The fact that J1019 is in a binary implies that we can constraint its mass, which allows us to (a) test dynamo scaling theories which predict the B-field strength of brown dwarfs/gas-giant exoplanet, and (b) study magnetospheric interactions which may be powering J1019’s radio emission. In this talk, I will present our latest radio observations of J1019 from 3 different telescopes (LOFAR, VLA, and GMRT). I will show that J1019 exhibits pulsed coherent emission that repeats on hour-timescale and present our latest efforts to find a cutoff in J1019’s radio spectrum to directly measure its B-field strength.

Speaker: Timothy Wing Hei Yiu (ASTRON)

117 VLBI with LOFAR and the EVN to resolve the structure of relativistic outflows in gamma-ray binaries

Gamma-ray binaries are unique laboratories for studying the interplay between relativistic outflows and dense stellar winds, producing variable non-thermal emission radio to very-high-energy (TeV) gamma rays. Resolving the spatial structure and evolution of the radio-emitting regions is essential for understanding the mechanisms driving particle acceleration and non-thermal emission in these systems. Howeevr, so far we only know nine of these systems and they have not been studied in detail at low frequencies. The synergy between LOFAR-VLBI, with its unprecedented sensitivity and sub-arcsecond resolution at the lowest radio frequencies, and the European VLBI Network (EVN), which provides high-resolution imaging at higher frequencies, enables a comprehensive multi-frequency investigation of gamma-ray binaries. This combined approach allows for tracing the morphology and evolution of the shocked material formed at the interaction zones between the relativistic wind of the young non-accreting neutron star and the stellar wind of the massive (O or B spectral type) companion. By mapping the extended and compact radio emission across a wide frequency range, we can trace the origin of the radio emission and its connection to the high-energy processes, ultimately advancing our understanding of particle acceleration and energy dissipation in these extreme binary systems. In this talk I summarize the first initiatives in this direction and how potential LOFAR+EVN observations would resolve the current unknowns from these particular sources.

Speaker: Benito Marcote (Joint Institute for VLBI ERIC)

118 Hunting Radio Bursts from Exoplanets and Brown Dwarfs with NenuFAR

Despite decades of effort, the detection of low-frequency radio emission from exoplanetary systems remains an open challenge. In this talk, we will present recent results from NenuFAR, including a tentative 6σ detection of a radio burst toward the well-studied hot Jupiter system HD 189733. The highly circularly polarized burst is consistent with coherent emission mechanisms such as the cyclotron maser instability (CMI). We explore potential origins including star-planet interactions (SPI), stellar magnetic activity, and background contamination. We will also briefly mention other potential burst candidates detected with NenuFAR from systems hosting exoplanets and brown dwarfs, illustrating both the promise and the current limitations of low-frequency transient searches in the substellar regime.

Speaker: Xiang Zhang (Observatoire de Paris - CNRS)

119 Expanding the search of radio exoplanets using the LOFAR Decameter Sky Survey (LoDeSS)

Gas-giant exoplanets are expected to generate low-frequency radio emission (< 40 MHz) via the cyclotron maser mechanism. Detecting this emission is likely the only viable way to measure exoplanets’ magnetic field and space-weather conditions. Despite many attempts, there has not been a confirmed detection of an exoplanet in the radio band. I will present results from our ongoing search for exoplanetary radio signals with the LOFAR telescope. Our primary focus has been on Tau Bootis b, which is currently the most promising candidate for radio emission. However, we are expanding our search into a significant fraction of the Northern sky, thanks to a new decameter survey (LoDeSS). I will describe our efforts to successfully overcome high levels of radio interference and the rapidly changing ionospheric conditions to obtain reliable radio images down to 15 MHz. I will conclude with key lessons learned and a critical test of radiometric scaling laws that predict the radio flux from magnetized planets.

Speaker: Cristina-Maria Cordun (ASTRON)

12:45 Conclusion