2003ApJ...594..732K

We investigate theoretical models for the radio halo and hard X-ray (HXR) excess in the Coma galaxy cluster. Time-independent and time-dependent reacceleration models for relativistic electrons have been carried out to study the formation of the radio halo and HXR excess. In these models, the relativistic electrons are injected by merger shocks and reaccelerated by ensuing violent turbulence. The effects of different Mach numbers of the merger shocks on the radio and HXR excess emission are also investigated. We adopt 6 µG as the central magnetic field and reproduce the observed radio spectra via the synchrotron emission. We also obtain a central ``plateau'' in the distribution of the radio spectral-indices, which have been observed in the radio emission distribution. Our models can also produce the observed HXR excess emission via the inverse Compton scattering of the cosmic microwave background photons. We find that only the merger shocks with Mach numbers around 1.6-2 can produce results in agreement with both the radio and HXR emission in the Coma Cluster.