First detection at 5.5 and 9 GHz of the radio relics in bullet cluster with ATCA

TL;DR

This study reports the first detection of diffuse radio relics in the Bullet cluster at 5.5 and 9 GHz, revealing spectral steepening and supporting models involving shock acceleration or turbulence.

Contribution

First high-frequency observations of Bullet cluster relics, confirming spectral steepening and discussing implications for particle acceleration models.

Findings

Detection of diffuse emission at 5.5 and 9 GHz

Spectral index steepening at frequencies above 5 GHz

Spectral fitting with a broken power law

Abstract

We present here results from observations at 5.5 and 9 GHz of the Bullet cluster 1E 0657-55.8 with the Australia Telescope Compact Array (ATCA). Our results show detection of diffuse emission in the cluster. Our findings are consistent with the previous observations by Shimwell et al. (2014) and Shimwell et al. (2015) at 1.1-3.1 GHz. Morphology of diffuse structures (relic regions A and B and the radio halo) are consistent with those reported by the previous study. Our results indicate steepening in the spectral index at higher frequencies (at and greater than 5.0 GHz) for region A. The spectrum can be fit well by a broken power law. We discuss the possibility of a few recent theoretical models explaining this break in the power law spectrum, and find that a modified Diffusive Shock Acceleration (DSA) model or a turbulent reacceleration model may be relevant. Deep radio observations at high frequencies (at and greater than 5 GHz) are required for a detailed comparison with this model.