Electron Heating and Acceleration at Galaxy Cluster Shocks: Insights from NuSTAR

Mergers between galaxy clusters drive weak shock fronts into the intracluster medium, capable of both heating the gas and accelerating relativistic particles. Measurements of the high temperature gas and non-thermal inverse Compton (IC) emission that result from these shocks most benefit from sensitive observations at hard X-ray energies. Recent observations of the massive merging clusters Abell 2163, Abell 665, and the Bullet cluster with NuSTAR, the first focusing hard (>10 keV) X-ray observatory, improve measurements of both thermal and IC components in each cluster. In the Bullet Cluster, we jointly fit long Chandra and NuSTAR observations--totaling 1 Ms--to constrain the temperature of the bow shock and determine whether electrons are directly heated by the shock front as previously suggested by Chandra data alone. We also preview NuSTAR constraints on the temperature of the recently discovered shock in Abell 665 and on the flux of IC emission from the electrons producing radio halos in all three clusters.