Speaker
Description
As we know, the ionosphere is of key importance in the context of long-wave radiation transfer from outer regions to ground. Therefore, good knowledge and predictability related to the shape and dynamics of the ionosphere is extremely important for the LOFAR system [1] to exclude the influence of this closest obstacle in the observational data of astrophysical objects.
On the other hand, good knowledge of the signal entering and passing through the ionosphere provides an additional and independent of standard techniques (GNSS) study of the ionosphere. What is extremely helpful is that the LOFAR system is an extremely sensitive tool for observing flux changes. This is exploited by observing bright sources such as CasA or CygA. See for example [2].
During the presentation, results of the analysis of pulsar data for the study of the ionosphere will be presented. Already published work related to the influence of the ionosphere on pulsar signals [3] have now been extended to include studies of ionospheric-related structures visible in dynamic spectra. At the same time, because the results of pulsar observations are often reduced to average profiles, the influence of the ionosphere is not considered when studying these objects. However, for pulsars with strong pulse fluxes, we can analyze the case of a sequence of single pulses or average the results over several periods.
As we cannot determine absolute fluxes from observations of individual LOFAR stations, dynamic spectra are constructed based on instantaneous S/N (signal to noise) values. Comparative analysis of such a signal with the results of TEC (Total Electron Content) measurements carried out by GNSS services and analysis of variability allow for determining the dynamics of changes in the direction of the observed source. To determine the dynamics of changes in the signal received by the LOFAR station, the PSI – Pulsar Scintillation Index calculation, based on S4 index described in [4,5] is used.
Initial data show the presence of quasi-periodic changes, which gives hope for the possibility of further analyzes related to TID structures and increase knowledge on spatiotemporal disturbances of the ionospheric plasma. We will also present the first correlation results between the dynamic spectra of selected pulsars observed simultaneously with polish PL612 and PL611 LOFAR stations.
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. 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.
4. 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
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
