Detection of a Double Relic in the Torpedo Cluster: SPT-CL J0245-5302

TL;DR

This paper reports the discovery of a double radio relic system in the merging Torpedo cluster at z=0.3, using multi-frequency radio observations to characterize shock properties and diffuse emission.

Contribution

It presents the first detection and analysis of two previously unknown radio relics in the Torpedo cluster, revealing its double relic nature at moderate redshift.

Findings

Detection of two new radio relics on the cluster periphery.

Spectral index of diffuse emission is approximately -1.63.

Radio-derived Mach number of the shock is about 2.04.

Abstract

The Torpedo cluster, SPT-CL J0245-5302 (S0295) is a massive, merging cluster at a redshift of z = 0.300, which exhibits a strikingly similar morphology to the Bullet cluster 1E 0657-55.8 (z = 0.296), including a classic bow shock in the cluster's intra-cluster medium revealed by Chandra X-ray observations. We present Australia Telescope Compact Array data centred at 2.1 GHz and Murchison Widefield Array data at frequencies between 72 MHz and 231 MHz which we use to study the properties of the cluster. We characterise a number of discrete and diffuse radio sources in the cluster, including the detection of two previously unknown radio relics on the cluster periphery. The average spectral index of the diffuse emission between 70 MHz and 3.1 GHz is $\alpha=-1.63_{-0.10}^{+0.10}$ and a radio-derived Mach number for the shock in the west of the cluster is calculated as M = 2.04. The Torpedo cluster is thus as a double relic system at moderate redshift.