Abstract
Very high energy observations of AGNs and microquasars are challenging current theories of particle acceleration (mostly based on shock acceleration) which have to explain how particles are accelerated to energies above TeV in very compact regions compared to the characteristic scales of their sources. The identification of microquasars and AGNs as sites of particle acceleration raises many fascinating and important questions. Recent magneto-hydrodynamical studies have revealed that cosmic ray acceleration by fast magnetic reconnection can be rather efficient because a first-order Fermi process may occur. In this work, we discuss this acceleration mechanism in the coronal region of the accretion disk around microquasars and AGNs. In addition, the accelerated particles lose substantial amounts of their energy due to non-thermal interactions with the surrounding magnetic field, matter and radiation fields. We compute the corresponding acceleration rate and the relevant loss rates in order to reproduce the observed spectral energy distribution for two microquasars (Cygnus-X1, Cygnus-X3), considering the model above and leptonic and hadronic processes.
