Radiation induced by relativistic electron showers in the X-ray spectrum of Active Galactic Nuclei

Abstract

The iron Kalpha emitted from accreting black holes is thought to be produced by the reprocessing of hard X-ray radiation illuminating the disk. Mechanisms which could produce this hard X-ray radiation are magnetic reconnection in the disk corona or shocks. Both phenomena produce high energy particles whose contribution is usually ignored. In this work, we analyze how the transfer of mechanical energy from relativistic electrons to the circumnuclear gas ( accretion disk, BLR) contributes to the X-ray continuum and the iron Ka emission. It is shown that for gas columns comparable to the Thomson depth, the iron Ka yield is comparable to that observed provided that the electron energy is above similar to 600 keV and that the total kinetic luminosity of the beam is around log L-KIN = 46.6- 47.7; this luminosity is comparable to that observed in radio-loud AGNs. The photon index of the X-ray continuum ( 8 keV- 20 keV) generated in such an electron shower is 1 less than or equal to Gamma less than or equal to 2. Gamma and the continuum strength are strongly model-dependent; they are dependent on both the relative orientation between the electron beam and the observer and the radius of the electron beam compared with the characteristic radius of the absorbing medium. The relevance of particle energy transport compared to photon energy transport in the AGN environment is outlined.