Speaker
Description
Radio relics are one kind of diffuse synchrotron emission that can be observed in merging galaxy cluster's outskirts, believed to trace particle (re-)acceleration by ICM shock waves. They show elongated shapes in the $\sim$Mpc scales and brightness distributions peaking at the shock location, decreasing toward cluster center. Two relics can be generated by a single merger event and be observed as a double-relic system, in which the near to the plane of the sky merger axis allows for a simple geometry and minimalized projection effects.
Recent high-resolution studies of radio relics revealed their filamentary structure, exposing the presence of many small-scale substructures, generating morphologies that are challenging to explain with simple systems. The origin of these filaments is yet unknown, and can be connected with complex shock surfaces or a complex magnetic field structure.
In this work, we studied the double-relic galaxy cluster MACS J1752.0+4440 at four frequencies: 144MHz (LOFAR), 416MHz and 650MHz (uGMRT) and 1.6GHz (JVLA), performing a high-resolution spectral and curvature study of both relics, observing a filamentary substructure along the North-East (NE) relic. The surface brightness and spectral index profiles highlight the presence of the filament along the NE relic. Color-color plots show that no spectral curvature is observed in the bandwidth. Furthermore, the integrated spectral index is surprisingly flatter than what predicted by DSA theory.
These features cannot be reproduced with simple assumptions and are likely the result of either a complex Mach number shock surface or strong projection effects at the shock location, which suggest caution is needed on the interpretation of double-relic systems.
