A $\mathcal{M}\gtrsim3$ shock in `El Gordo' cluster and the origin of the radio relic

TL;DR

This study analyzes a distant galaxy cluster 'El Gordo' revealing a strong shock and radio relics, supporting the connection between shocks and radio relics and suggesting shock acceleration from thermal particles as a plausible origin.

Contribution

First detailed analysis of a $E;3$ shock in a high-redshift galaxy cluster, linking shock properties with radio relics and exploring their origin.

Findings

Detection of a strong $E;3$ shock at the cluster periphery.

Radio relics overlap with X-ray emission, indicating a shock-relic connection.

Shock acceleration from thermal particles remains a viable explanation.

Abstract

We present an X-ray and radio study of the famous `El Gordo', a massive and distant ($z=0.87$) galaxy cluster. In the deep (340 ks) Chandra observation, the cluster appears with an elongated and cometary morphology, a sign of its current merging state. The GMRT radio observations at 610 MHz reveal the presence of a radio halo which remarkably overlaps the X-ray cluster emission and connects a couple of radio relics. We detect a strong shock ($\mathcal{M}\gtrsim3$) in the NW periphery of the cluster, co-spatially located with the radio relic. This is the most distant ($z=0.87$) and one of the strongest shock detected in a galaxy cluster. This work supports the relic-shock connection and allows to investigate the origin of these radio sources in a uncommon regime of $\mathcal{M}\gtrsim3$. For this particular case we found that shock acceleration from the thermal pool is still a viable possibility.