An upgraded GMRT and MeerKAT study of radio relics in the low mass merging cluster PSZ2 G200.95-28.16

Abstract

Diffuse radio sources known as radio relics are direct tracers of shocks in the outskirts of merging galaxy clusters. PSZ2 G200.95-28.16, a low-mass merging cluster($\textrm{M}_{500} = (2.7 \pm 0.2) \times 10^{14}~\mathrm{M}_{\odot}$) features a prominent radio relic, first identified by Kale et al. 2017. We name this relic as the Seahorse. The MeerKAT Galaxy Cluster Legacy Survey has confirmed two additional radio relics, R2 and R3 in this cluster. We present new observations of this cluster with the Upgraded GMRT at 400 and 650 MHz paired with the Chandra X-ray data. The largest linear sizes for the three relics are~1.53 Mpc, 1.12~kpc, and 340~kpc. All three radio relics are polarized at 1283~MHz. Assuming the diffusive shock acceleration model, the spectral indices of the relics imply shock Mach Numbers of $3.1 \pm 0.8$ and $2.8 \pm 0.9$ for the Seahorse and R2, respectively. The Chandra X-ray surface brightness map shows two prominent subclusters, but the relics are not perpendicular to the likely merger axis as typically observed; no shocks are detected at the locations of the relics. We discuss the possible merger scenarios in light of the low mass of the cluster and the radio and X-ray properties of the relics. The relic R2 follows the correlation known in the radio relic power and cluster mass plane, but the Seahorse and R3 relics are outliers. We have also discovered a radio ring in our 650~MHz uGMRT image that could be an Odd radio circle candidate.