Non-thermal emission from relativistic accretion disks: A simple model for axisymmetric inhomogeneous sources

The thin relativistic disk model of Novikov and Thorne (1973) is used to investigate the properties of non-thermal spectra emitted by axisymmetric inhomogeneous sources under the assumption that fast particles are produced by the reconnection of magnetic fields. Spectra are computed for power law and monoenergetic electron distributions in the case where the acceleration and emission regions are coincident, the maximum electron energy being determined by a balance between energy gain and losses, and also in the case where the electrons are accelerated without significant losses before beginning to radiate. If applied to galactic X-ray sources, this model suggests that the mildly relativistic (Lorentz factor approx. equal to20) electron population thus produced could possibly play a part in the comptonization of thermal photons to hard X-ray energies. In the case of active galactic nuclei, although their associated supermassive accretion disks are more likely to be of the thick type, the results for the thin model are highly suggestive and provide some insight into features expected from thick disk models. An attractive feature of this simple model is that, for both galactic and extragalactic applications, the production of fast particles depends upon the third power of the mass accretion rate M. A slight increase in M would thus be sufficient to trigger a change of state or outburst. (orig.)