| Abstract : | Merging galaxy clusters typically exhibit traces of diffuse radio emissions in the form of radio relics and halos. Radio relics are arc-like polarized radio sources typically found at the cluster peripheries. These are believed to be the products of the interaction of re-accelerated Cosmic Ray electrons with cluster magnetic fields tracing the merger shocks. Re-acceleration mechanisms like diffusive shock acceleration (DSA) can explain most of the properties of radio relics although the re-acceleration efficiency is found to be inadequate in several cases. Higher-mass ( >5 x 10^14 solar masses) cluster mergers are more prone to exhibit powerful diffuse radio emissions than lower-mass mergers as the higher-mass mergers normally involve more energy in the merger dynamics. Under the accepted framework, the low-mass mergers have an energy deficit to produce high luminosity radio relics. However, there are several cases (PLCK G200, Abell 168, Abell 3627-bis) where low-mass cluster mergers are found to host radio relics which are order of magnitude more powerful than predicted by the accepted theories. How these low-mass cluster mergers result in multiple relics is still not understood well within the framework of proposed models like DSA.
Kale et al. 2017 discovered a radio relic in the low-mass (2.4 x 10^14 solar masses) galaxy cluster merger PLCK G200-28.2 with GMRT and VLA. MeerKAT Galaxy Cluster Legacy Survey detected two new radio relics in the cluster. We will present uGMRT 400, 650 MHz, and MeerKAT 1283 MHz images and discuss the spectral and polarization properties of these three radio relics. We will also present the high-exposure Chandra X-ray data (149 ks) to re-construct the merger history and dynamics. We will discuss the merger scenario emerging from the detection of these relics and shed light on the possible physical mechanisms involved in the formation of multiple radio relics in low-mass mergers. |
