A shock front at the radio relic of Abell 2744
Kneib, J. -P.; Eckert, D.; Vazza, F.; Knowles, K.; Jauzac, M.; Intema, H.; Owers, M. S.; Tchernin, C.
Switzerland, United Kingdom, South Africa, Germany, Australia, Netherlands, United States
Abstract
Radio relics are Mpc-scale diffuse radio sources at the peripheries of galaxy clusters which are thought to trace outgoing merger shocks. We present XMM-Newton and Suzaku observations of the galaxy cluster Abell 2744 (z = 0.306), which reveal the presence of a shock front 1.5 Mpc east of the cluster core. The surface-brightness jump coincides with the position of a known radio relic. Although the surface-brightness jump indicates a weak shock with a Mach number M=1.7_{-0.3}^{+0.5}, the plasma in the post-shock region has been heated to a very high temperature (∼13 keV) by the passage of the shock wave. The low-acceleration efficiency expected from such a weak shock suggests that mildly relativistic electrons have been re-accelerated by the passage of the shock front.