Deep VLA observations of the cluster 1RXS J0603.3+4214 in the frequency range 1-2 GHz

TL;DR

This study presents high-resolution VLA observations of the galaxy cluster 1RXS J0603.3+4214, revealing detailed structures of the radio relic and halo, and providing insights into magnetic fields, shock properties, and the correlation between radio and X-ray emissions.

Contribution

It offers the first high-resolution, sensitive imaging of the cluster's radio relic and halo, combined with spectral analysis and modeling to understand shock acceleration and magnetic field variations.

Findings

The Toothbrush relic has a narrow ridge with a spectral index of -0.70 to -0.80.

The magnetic field in the relic is below 5 microGauss and varies across the shock.

The Mach number of the shock is approximately 3.78, consistent with spectral data.

Abstract

We report L-band VLA observations of 1RXS J0603.3+4214, a cluster that hosts a bright radio relic, known as the Toothbrush, and an elongated giant radio halo. These new observations allow us to study the surface brightness distribution down to one arcsec resolution with very high sensitivity. Our images provide an unprecedented detailed view of the Toothbrush, revealing enigmatic filamentary structures. To study the spectral index distribution, we complement our analysis with published LOFAR and GMRT observations. The bright `brush' of the Toothbrush shows a prominent narrow ridge to its north with a sharp outer edge. The spectral index at the ridge is in the range $-0.70\leq\alpha\leq-0.80$. We suggest that the ridge is caused by projection along the line of sight. With a simple toy model for the smallest region of the ridge, we conclude that the magnetic field is below $5\,\rm\mu G$ and varies significantly across the shock front. Our model indicates that the actual Mach number is higher than that obtained from the injection index and agrees well with the one derived from the overall spectrum, namely ${\cal M}=3.78^{+0.3}_{-0.2}$. The radio halo shows an average spectral index of $\alpha=-1.16\pm0.05$ and a slight gradient from north to south. The southernmost part of the halo is steeper and possibly related to a shock front. Excluding the southernmost part, the halo morphology agrees very well with the X-ray morphology. A power-law correlation is found between the radio and X-ray surface brightness