Speaker
Description
Radio relics are extended diffuse sources that are thought to originate from shock fronts caused by galaxy cluster mergers and are found at the periphery of many dynamically disturbed clusters. However, the particle acceleration mechanism at the shock fronts and the formation of the relics is not yet well understood. A spectacular, large-scale extended radio relic has been found in the galaxy cluster Abell 115 (A115). The X-ray properties of the intra-cluster medium (ICM) in A115 are characterized by a double surface brightness peak, suggesting the presence of two sub-clusters in a merging process. The diffuse radio emission has an unusual morphology, atypical for a relic, as it extends well into the low-density ICM and does not follow the X-ray surface brightness isophotes. We present new wideband radio continuum observations with the VLA (combined B and C configuration) in L-band and the uGMRT in Band band 4, which allows us to study the relic with high sensitivity and high spatial resolution. Our studies of the spectral properties of the relic at the frequencies of 700 MHz and 1.5 GHz reveal the puzzling property that the integrated spectral index is almost uniform along the length of the relic, despite the significant change in ICM density along the relic. We investigated how the peak radio surface brightness along the relic correlates with X-ray surface brightness and discuss the consequences for formation scenarios of radio relics. Moreover, our observations also allow us to identify a new arc-shaped radio diffuse structure to the west of 3C28, which had not been detected before. This emission is possibly connected to a weak shock front relatively nearby to the center of the northern subcluster.
