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This is the second paper in a series of studies of the Coma cluster using theSRG/eROSITA X-ray data obtained during the calibration and performanceverification phase of the mission. Here, we focus on the region adjacent to theradio source 1253+275 (radio relic, RR, hereafter). We show that the X-raysurface brightness exhibits its steepest gradient at $\sim 79'$ ($\sim2.2\,{\rm Mpc}\approx R_{200c}$), which is almost co-spatial to the outer edgeof the RR. As in the case of several other relics, the Mach number of the shockderived from the X-ray surface brightness profile ($M_X\approx 1.9$) appears tobe lower than needed to explain the slope of the integrated radio spectrum inthe diffusive shock acceleration (DSA) model ($M_R\approx 3.5$) if the magneticfield is uniform and the radiative losses are fast. However, the shock geometryis plausibly much more complicated than a spherical wedge centered on thecluster, given the non-trivial correlation between radio, X-ray, and SZ images.While the complicated shock geometry alone might cause a negative bias in$M_X$, we speculate on a few other possibilities that may affect the$M_X$-$M_R$ relation, including the shock substructure that might be modifiedby the presence of non-thermal filaments stretching across the shock and thepropagation of relativistic electrons along the non-thermal filaments with astrong magnetic field. We also discuss the "history" of the radio galaxyNGC4789, which is located ahead of the relic in the context of the Coma-NGC4839merger scenario.

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