MeerKAT's View of the Bullet Cluster 1E 0657-55.8

TL;DR

This paper presents high-resolution MeerKAT radio observations of the Bullet cluster, revealing an extended radio halo and relic, with spectral analysis indicating primary re-acceleration and a higher Mach number for the relic shock than X-ray estimates.

Contribution

The study provides the first detailed MeerKAT imaging of the Bullet cluster's radio halo and relic, extending known structures and analyzing spectral and shock properties with improved accuracy.

Findings

Extended radio halo of 1.6 Mpc x 1.3 Mpc

Largest relic size ~988 kpc

Radio Mach number M_R= 4.6±0.9, higher than X-ray estimates

Abstract

The Bullet cluster (1E 0657-55.8) is a massive merging system at redshift $z$=0.296, known to host a powerful radio halo and a relic. Here we present high fidelity MeerKAT L-band (0.9-1.7 GHz) observations of the Bullet cluster, in which we trace a larger extent of both the radio halo and relic in comparison to previous studies. The size of the recovered radio halo is 1.6 Mpc $\times$ 1.3 Mpc and the largest linear size of the relic is ~988 kpc. We detect a new decrement feature on the southern outskirts of the halo emission, where a region appears to have a lower surface brightness in comparison to its surroundings. The larger extension on the outskirts of the halo is faint, which suggests lower relativistic electron density or a weaker magnetic field. An in-band spectral index map of the radio halo reveals a hint of radial steepening towards the edges of the diffuse source, likely due to synchrotron electron ageing. The integrated spectral index of the radio halo is 1.1$\pm$0.2. We perform a radio-X-ray surface brightness point-to-point analysis, which reveals a linear correlation for the radio halo. This indicates that the radio halo emission is produced by primary re-acceleration mechanisms. Finally, we derive a radio Mach number of M_R= 4.6$\pm$0.9 for the relic shock region, which is higher than the Mach number inferred by earlier analyses based on X-ray data. Discrepancies between radio and X-ray Mach numbers have been observed for multiple systems, with studies suggesting that this is due to various factors, including relic orientation.