Nonthermal Phenomena in Clusters of Galaxies

Recent observations of high energy (> 20 keV) X-ray emission in a few clusters extend and broaden our knowledge of physical phenomena in the intracluster space. This emission is likely to be nonthermal, probably resulting from Compton scattering of relativistic electrons by the cosmic microwave background radiation. Direct evidence for the presence of relativistic electrons in some ∼ 30 clusters comes from measurements of extended radio emission in their central regions. I first review the results from RXTE and BeppoSAX measurements of a small sample of clusters, and then discuss their implications on the mean values of intracluster magnetic fields and relativistic electron energy densities. Implications on the origin of the fields and electrons are briefly considered.