Particle injection and reacceleration in clusters of galaxies and the EUV excess: the case of Coma

We calculate the energy distribution of the relativistic particles injected in the ICM during a phase of reacceleration of the relativistic particles in the cluster volume. We apply our results to the case of the Coma cluster in which recent merging activity and the presence of a radio halo may sugg est that reacceleration processes are efficient. We find that the electron population injected in the central part of the cluster by the head tail rad io galaxy NGC 4869 may account for a large fraction, if not all, of the det ected EUV excess via inverse Compton scattering of the cosmic microwave bac kground (CMB) photons. If radio haloes are powered by reacceleration mechan isms active in the cluster volume, moderate non-thermal EUV excesses (of th e order similar to1-5.10(42) erg s(-1)) should be a common feature of clust ers containing powerful head tail radio galaxies and/or AGNs. (C) 2001 Else vier Science B.V. All rights reserved.