Evidence for an X-Ray to Gamma-Ray Virial Shock Signal from the Coma Cluster

Abstract

Following evidence for an east–west elongated virial ring around the Coma galaxy cluster in a ∼220 GeV VERITAS mosaic, we search for corresponding signatures in >GeV γ -rays from Fermi -Large Area Telescope (LAT), and in soft, ∼0.1 keV X-rays from ROSAT . For the ring elongation and orientation inferred from VERITAS, we find a nominal LAT excess, and the expected signature ( ) in ROSAT bands R1 and R1+R2. The significances of both LAT and ROSAT signals are maximal near the VERITAS ring parameters. The intensities of the ROSAT , Fermi , and VERITAS signals are consistent with the virial shock depositing (with an uncertainty factor of ∼3) of its energy over a Hubble time in a nearly flat, spectrum of cosmic-ray electrons. The sharp radial profiles of the LAT and ROSAT signals suggest preferential accretion in the plane of the sky, as indicated by the distribution of neighboring large-scale structures. The X-ray signal gauges the compression of cosmic-rays as they are advected deeper into the cluster.