SIMBAD references

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, where we trace a larger extent of both the halo and relic in comparison to previous studies. The size of the recovered halo is 1.6 Mpc × 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 halo reveals radial steepening towards the edges, likely due to synchrotron electron ageing. The integrated spectral index of the radio halo is 1.1 ± 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 halo emission is produced by primary re-acceleration mechanisms. Finally, we derive a radio Mach number of $\mathcal {M}_R$ = 4.6 ± 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, studies suggest that this is due to various factors, including relic orientation.