Thursday

Radio relics are diffuse extended sources thought to be produced by merger driven shock fronts in the outskirts of galaxy clusters. The spectral properties of relics provide useful information about the energy spectrum of the relativistic particles and the magnetic field distribution in galaxy clusters. We present a multi-frequency study of the diffuse radio emission associated with cluster 1RXS J0603.3+4214. The cluster hosts one of the most intriguing relics, known as Toothbrush. We also present new JVLA observations of the Toothbrush at 1-2 GHz which reveal enigmatic filamentary structures. With a multi-frequency study, we provide evidence that the filamentary structures associated with the Toothbrush are not just filaments of enhanced emission. The high-fidelity LOFAR images allowed us, for the first time, to study the spectral index distribution of the Toothbrush at 4.5 arcsec resolution. The high resolution spectral index map, between 150 MHz to 1.5 GHz, reveal a flat spectrum at the northern shock, namely $\alpha=-0.70$ to $-0.75$. Our results emphasise that the actual injection spectrum is flatter than the one measured from the spectral index maps. The surface brightness distribution, considering shock and downstream aging model, indicates that there are significant variations of the magnetic field strength along the line of sight. The downstream spectral profile at 150 MHz, 610 MHz and 1.5 GHz, can be explained by an inhomogeneous magnetic field and high Mach number shock (${\hfil \mathcal{M}}=3.7$). The spectral profiles rules out field strength above about 5 $\mu $G.