Cluster mergers leave distinct signatures in the ICM in the form of shocks and diffuse cluster radio sources that provide evidence for the acceleration of relativistic particles .
However , the physics of particle acceleration in the ICM is still not fully understood .
Here we present new 1–4 GHz Jansky Very Large Array ( VLA ) and archival Chandra observations of the HST Frontier Fields Cluster \object Abell 2744 .
In our new VLA images , we detect the previously known \sim 2.1 Mpc radio halo and \sim 1.5 Mpc radio relic .
We carry out a radio spectral analysis from which we determine the relic ’ s injection spectral index to be \alpha _ { inj } = -1.12 \pm 0.19 .
This corresponds to a shock Mach number of \mathcal { M } = 2.05 ^ { +0.31 } _ { -0.19 } under the assumption of diffusive shock acceleration .
We also find evidence for spectral steepening in the post-shock region .
We do not find evidence for a significant correlation between the radio halo ’ s spectral index and ICM temperature .
In addition , we observe three new polarized diffuse sources and determine two of these to be newly discovered giant radio relics .
These two relics are located in the southeastern and northwestern outskirts of the cluster .
The corresponding integrated spectral indices measure - 1.81 \pm 0.26 and - 0.63 \pm 0.21 for the SE and NW relics , respectively .
From an X-ray surface brightness profile we also detect a possible density jump of R = 1.39 ^ { +0.34 } _ { -0.22 } co-located with the newly discovered SE relic .
This density jump would correspond to a shock front Mach number of \mathcal { M } = 1.26 ^ { +0.25 } _ { -0.15 } .