Shocks and Nonthermal Processes in Clusters

Abstract

Clusters of galaxies generally form by the gravitational merger of smaller clusters and groups. Major cluster mergers are the most energetic events in the Universe since the Big Bang. Mergers drive shocks into the intracluster gas, and these shocks heat the intracluster gas, and should also accelerate nonthermal relativistic particles. The X-ray signatures of the thermal effects of merger shocks will be discussed. X-ray observations of shocks can be used to determine the geometry and kinematics of the merger. As a result of particle acceleration in shocks, clusters of galaxies should contain very large populations of relativistic electrons and ions. Electrons with Lorentz factors gamma~300 (energies E = gamma m_e c^2 ~ 150 MeV) are expected to be particularly common. Observations and models for the radio, extreme ultraviolet, hard X-ray, and gamma-ray emission from nonthermal particles accelerated in these shocks will also be described. The predicted gamma-ray fluxes of clusters should make them easily observable with GLAST.