Probing the Merger in ACT-CL J0256.5+006: Understanding Low-Power Radio Halos

ACT-CL J0256.5+0006 (J0256) is a moderate redshift (z=0.363) merging cluster. Around it, one of the weakest known cluster giant radio halos has been observed. Based on our ACT SZ detection and a very short XMM observation, J0256 has the weakest SZ and possibly the lowest mass ever observed for a radio halo as well. Our Chandra observation gives J0256’s dynamical merger state: it is an early-stage merger, which challenges the theory that radio halos are produced by turbulent re-acceleration after the passage of merger shocks. It is also possible that this merger is a late-stage merger, and the observed structures are simply due to projection effects caused by the merger’s orientation with respect to our line of sight. This possibility will also be investigated.