Nonthermal emission from relativistic electrons in clusters of galaxies: Amerger shock acceleration model

We have investigated evolution of nonthermal emission from relativistic ele ctrons accelerated around the shock fronts during mergers of clusters of ga laxies. We estimate synchrotron radio emission and inverse Compton scatteri ng of cosmic microwave background photons from extreme ultraviolet (EUV) to hard X-ray range. The hard X-ray emission is most luminous in the later st age of a merger. Both hard X-ray and radio emissions are luminous only whil e signatures of merging events are clearly seen in the thermal intracluster medium (ICM). On the other hand, EW radiation is still luminous after the system has relaxed. Propagation of shock waves and bulk-flow motion of ICM play crucial roles in extending radio halos. In the contracting phase, radi o halos are located at the hot region of ICM or between two substructures. In the expanding phase, on the other hand, radio halos are located between two ICM hot regions and show rather diffuse distribution.