This is the second paper in a series of studies of the Coma cluster using the SRG/eROSITA X-ray data obtained in the course of the calibration and performance verification observations. Here we focus on the region adjacent to the radio source 1253+275 (Radio Relic, RR hereafter). We show that the X-ray surface brightness steepest gradient at ∼ 79 (∼ 2.2 Mpc ≈ R 200c ) is almost co-spatial with the outer edge of RR, with an offset of about ∼ 100−150 kpc between the derived position of the shock front and the brightest part of RR. As in several other relics, the Mach number of the shock derived from the X-ray surface brightness profile (M X ≈ 1.9) appears to be lower than needed to explain the slope of the integrated radio spectrum in the DSA model (M R ≈ 3.5) if the magnetic field is uniform and the radiative losses are fast. However, the shock geometry is plausibly much more complicated than a spherical wedge centered on the cluster, given a non-trivial correlation between radio, X-ray, and SZ images. While the complicated shock geometry alone might bias M X low, we speculate on a few other processes that can affect the M X -M R relation, including a fine structure of the shock that might be modified by the presence of non-thermal filaments stretching across the shock. We also discuss the "history" of the radio galaxy NGC4789 located ahead of the relic in the context of the Coma-NGC4839 merger scenario.

This is the second paper in a series of studies of the Coma cluster using the SRG/eROSITA X-ray data obtained during the calibration and performance verification phase of the mission. Here, we focus on the region adjacent to the radio source 1253+275 (radio relic, RR, hereafter). We show that the X-ray surface brightness exhibits its steepest gradient at ∼ 79 ′ (∼ 2.2 Mpc ≈ R 200c ), which is almost co-spatial to the outer edge of the RR. As in the case of several other relics, the Mach number of the shock derived from the X-ray surface brightness profile (M X ≈ 1.9) appears to be lower than needed to explain the slope of the integrated radio spectrum in the diffusive shock acceleration (DSA) model (M R ≈ 3.5) if the magnetic field is uniform and the radiative losses are fast. However, the shock geometry is plausibly much more complicated than a spherical wedge centered on the cluster, 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 modified by the presence of non-thermal filaments stretching across the shock and the propagation of relativistic electrons along the non-thermal filaments with a strong magnetic field. We also discuss the "history" of the radio galaxy NGC4789, which is located ahead of the relic in the context of the Coma-NGC4839 merger scenario.