Alfvenic reacceleration of relativistic particles in galaxy clusters in the presence of secondary electrons and positrons

Abstract

In a previous paper (Brunetti et al. 2004) we presented the first self-consistent calculations of the time-dependent coupled equations for the electrons, hadrons and Alfvén waves in the intracluster medium, which describe the stochastic acceleration of the charged particles and the corresponding spectral modification of the waves. Under viable assumptions, this system of mutually interacting components was shown to accurately describe several observational findings related to the radio halos in clusters of galaxies. In this paper, we add to the self-consistency of the calculations by including the generation and re-energization of secondary electrons and positrons, produced by the inelastic interactions of cosmic rays with the thermal gas in the intracluster medium. The bulk of Cosmic rays is expected to be confined within the cluster volume for cosmological times, so that the rate of production of secondary electrons, as well as gamma rays, may become correspondingly enhanced. If MHD waves are present, as it may be expected in the case of a recent merger event, then the reacceleration of secondary electrons and positrons can significantly affect the phenomenology of the non thermal processes in clusters. We investigate here these effects for the first time.