Galaxy Clusters in Theswift/Burst Alert Telescope Era: Hard X-Rays in the Intracluster Medium

We report the detection of 10 clusters of galaxies in the ongoing Swift /Burst Alert Telescope (BAT) all-sky survey. This sample, which mostly comprises merging clusters, was serendipitously detected in the 15–55 keV band. We use the BAT sample to investigate the presence of excess hard X-rays above the thermal emission. The BAT clusters do not show significant (e.g., ⩾2σ) nonthermal hard X-ray emission. The only exception is represented by Perseus whose high-energy emission is likely due to NGC 1275. Using XMM-Newton , Swift /XRT, Chandra and BAT data, we are able to produce upper limits of the inverse Compton (IC) emission mechanism which are in disagreement with most of the previously-claimed hard X-ray excesses. The coupling of the X-ray upper limits of the IC mechanism to radio data shows that, in some clusters, the magnetic field might be larger than 0.5 μG. We also derive the first log N –log S and luminosity function distributions of galaxy clusters above 15 keV.