Suzaku observations of a shock front tracing the western edge of the giant radio halo in the Coma Cluster

TL;DR

This study uses Suzaku X-ray observations to map a shock front along the western edge of the Coma Cluster's radio halo, revealing its extent, properties, and complex geometry, and linking it to particle acceleration processes.

Contribution

First detection of the full extent of the shock front along the Coma Cluster's radio halo edge using Suzaku, providing detailed temperature and brightness profiles.

Findings

Shock front extends northwards along the halo edge.

Mach number of the shock is approximately 1.5.

Shock geometry is complex and not spherically symmetric.

Abstract

We present the results of new Suzaku observations of the Coma Cluster, the X-ray brightest, nearby, merging system hosting a well studied, typical giant radio halo. It has been previously shown that, on the western side of the cluster, the radio brightness shows a much steeper gradient compared to other azimuths. XMM-Newton and Planck revealed a shock front along the southern half of the region associated with this steep radio gradient, suggesting that the radio emission is enhanced by particle acceleration associated with the shock passage. Suzaku demonstrates for the first time that this shock front extends northwards, tracing the entire length of the western edge of the Coma radio halo. The shock is detected both in the temperature and X-ray surface brightness distributions and has a Mach number of around $\mathcal{M}\sim1.5$. The locations of the surface brightness edges align well with the edge of the radio emission, while the obtained temperature profiles seem to suggest shocks located 125-185 kpc further out in radius. In addition, the shock strengths derived from the temperature and density jumps are in agreement when using extraction regions parallel to the radio halo edge, but become inconsistent with each other when derived from radial profiles centred on the Coma Cluster core. It is likely that, beyond mere projection effects, the geometry of the shock is more complex than a front with a single, uniform Mach number and an approximately spherically symmetric shape.