Particle Acceleration in Clusters of Galaxies

Clusters of galaxies have non-thermal high energy particles as well as the thermal intracluster medium in the intracluster space. One bit of direct evidence is the existence of non-thermal synchrotron radio halos and relics. However, it is still unclear how they are accelerated. Here, we consider two kinds of acceleration processes which likely work in the intracluster space and introduce models based on them. One is shock acceleration associated with cluster mergers. We calculate evolution of non-thermal electrons during cluster merger based on N-body + SPH simulations. Radio emission is localized near the shocks. This is qualitatively similar to radio relics. The other is resonant scattering of random Alfven waves. We calculate steady state electron distribution functions when Alfven wave power spectra are power-law. We successfully reproduce the Coma cluster radio halo spectrum.