Particle acceleration in cooling flow clusters of galaxies: The case of Abell 2626

¹ Institut für Astrophysik, Universität Innsbruck, Technikerstraße 25, 6020 Innsbruck, Austria
² Dipartimento di Astronomia, Università di Bologna, via Ranzani 1, 40127 Bologna, Italy
³ Istituto di Radioastronomia del CNR, via Gobetti 101, 40129 Bologna, Italy

Corresponding author: M. Gitti, Myriam.Gitti@uibk.ac.at

Received: 11 June 2003
Accepted: 24 November 2003

Abstract

Recently a theoretical model has been proposed that accounts for the origin of radio mini-halos observed in some cooling flow clusters as related to electron re-acceleration by MHD turbulence (Gitti et al. [CITE]). The MHD turbulence is assumed to be frozen into the flow of the thermal ICM and thus amplified in the cooling flow region. Here we present the application of this model to a new mini-halo candidate, the cluster A2626, and compare the results with those obtained for the mini-halo in the Perseus cluster. We present VLA data at 330 MHz and 1.5 GHz of the diffuse radio emission observed in A2626, and we show that its main properties can be explained by the model. We find that the power necessary for the re-acceleration of the relic electron population is only a factor of ~0.7% of the maximum power that can be extracted from the cooling flow (as estimated on the basis of the standard model). We also discuss the observational properties of known mini-halos in connection with those of host clusters, showing that the radio power of mini-halos increases with the maximum power of cooling flows. This trend is expected in the framework of the model. Possible effects of new Chandra and XMM-Newton estimates of on this trend are considered: we conclude that even if earlier derived cooling rates were overestimated, cooling flow powers are still well above the radio powers emitted by mini-halos.