High Energy X-Ray Emission in Clusters of Galaxies

Observations with the RXTE and SAX satellites have recently led to the measurement of a second component in the spectra of several clusters of galaxies which are known to have regions of extended radio emission. This new component is quite likely nonthermal emission resulting from Compton scattering of relativistic electrons by the cosmic microwave background. The nonthermal X-ray and radio measurements yield the values of the mean intracluster magnetic field, and relativistic electron density, for the first time in extragalactic environments. These results have important consequences on issues such as the origin of cosmic ray electrons and protons, their propagation modes in clusters, and the effects of these particles and magnetic fields on the intracluster gas. The observational results are reviewed, and some of their direct implications are discussed, along with near-future prospects for improved spectral and spatial measurements of nonthermal emission in clusters.