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Based on Suzaku X-ray observations, we study the hot gas around the NGC4839group of galaxies and the radio relic in the outskirts of the Coma cluster. Wefind a gradual decline in the gas temperature from 5 keV around NGC4839 to 3.6keV at the radio relic, across which there is a further, steeper drop down to1.5 keV. This drop as well as the observed surface brightness profile areconsistent with a shock with Mach number M = 2.2 pm 0.5 and velocity vs = (1410pm 110) km s^-1. A lower limit of B > 0.33 mu G is derived on the magneticfield strength around the relic from upper limits to inverse Compton X-rayemission. Although this suggests that the non-thermal electrons responsible forthe relic are generated by diffusive shock acceleration (DSA), the relationbetween the measured Mach number and the electron spectrum inferred from radioobservations are inconsistent with that expected from the simplest,test-particle theory of DSA. Nevertheless, DSA is still viable if it isinitiated by the injection of a pre-existing population of non-thermalelectrons. Combined with previous measurements, the temperature profile of Comain the southwest direction is shallower outside NGC4839 and also slightlyshallower in the outermost region. The metal abundance around NGC4839 isconfirmed to be higher than in its vicinity, implying a significant peak in theabundance profile that decreases to 0.2 solar toward the outskirts. Weinterpret these facts as due to ram pressure stripping of metal-enriched gasfrom NGC4839 as it falls into Coma. The relic shock may result from thecombined interaction of pre-existing intracluster gas, gas associated with NGC4839, and cooler gas flowing in from the large-scale structure filament in thesouthwest.

Suzaku X-Ray Observations of the Accreting NGC 4839 Group of Galaxies and the Radio Relic in the Coma Cluster