Tempestuous life beyond R500: X-ray view on the Coma cluster with SRG/eROSITA. II. Shock & Relic

This is the second paper in a series of studies Coma cluster using SRG/eROSITA X-ray data obtained during calibration and performance verification phase mission. Here, we focus on region adjacent to radio source 1253+275 (radio relic, RR, hereafter). We show that surface brightness exhibits its steepest gradient at $\sim 79'$ ($\sim 2.2\,{\rm Mpc}\approx R_{200c}$), which almost co-spatial outer edge RR. As case several other relics, Mach number shock derived from profile ($M_X\approx 1.9$) appears be lower than needed explain slope integrated spectrum diffusive acceleration (DSA) model ($M_R\approx 3.5$) if magnetic field uniform radiative losses are fast. However, geometry plausibly much more complicated spherical wedge centered cluster, given non-trivial correlation between radio, X-ray, SZ images. While alone might cause negative bias $M_X$, speculate few possibilities may affect $M_X$-$M_R$ relation, including substructure modified by presence non-thermal filaments stretching across propagation relativistic electrons along with strong field. also discuss "history" galaxy NGC4789, located ahead relic context Coma-NGC4839 merger scenario.