Despite progress in understanding radio relics , there are still open questions regarding the underlying particle acceleration mechanisms .
In this paper we present deep 1–4 GHz VLA observations of CIZA J2242.8+5301 ( z = 0.1921 ) , a double radio relic cluster characterized by small projection on the plane of the sky .
Our VLA observations reveal , for the first time , the complex morphology of the diffuse sources and the filamentary structure of the northern relic .
We discover new faint diffuse radio emission extending north of the main northern relic .
Our Mach number estimates for the northern and southern relics , based on the radio spectral index map obtained using the VLA observations and existing LOFAR and GMRT data , are consistent with previous radio and X-ray studies ( \mathcal { M } _ { RN } = 2.58 \pm 0.17 and \mathcal { M } _ { RS } = 2.10 \pm 0.08 ) .
However , color-color diagrams and modelings suggest a flatter injection spectral index than the one obtained from the spectral index map , indicating that projection effects might be not entirely negligible .
The southern relic consists of five “ arms ” .
Embedded in it , we find a tailed radio galaxy which seems to be connected to the relic .
A spectral index flattening , where the radio tail connects to the relic , is also measured .
We propose that the southern relic may trace AGN fossil electrons that are re-accelerated at a shock , with an estimated strength of \mathcal { M } = 2.4 .
High-resolution mapping of other tailed radio galaxies also supports a scenario where AGN fossil electrons are revived by the merger event and could be related to the formation of some diffuse cluster radio emission .