A shock front at the radio relic of Abell 2744

TL;DR

This study identifies a shock front associated with a radio relic in galaxy cluster Abell 2744, revealing a weak shock that heats plasma significantly and likely re-accelerates electrons, enhancing understanding of cluster merger dynamics.

Contribution

First detection of a shock front at the radio relic in Abell 2744 using X-ray observations, linking shock properties to radio relic features and electron re-acceleration.

Findings

Detected a shock front 1.5 Mpc from cluster core

Shock has a Mach number of approximately 1.7

Post-shock plasma heated to about 13 keV

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 $\mathcal{M}=1.7_{-0.3}^{+0.5}$, the plasma in the post-shock region has been heated to a very high temperature ($\sim13$ 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.