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

¹ Dipartimento di Fisica G. Occhialini, Universita' degli Studi di Milano-Bicocca, Pza. della Scienza 3, 20126 Milano, Italy
² Instituto de Astronomía y Geodesia (CSIC-UCM), Fac. de CC Matemáticas, Universidad Complutense, 28040 Madrid, Spain e-mail: aig@mat.ucm.es

Received: 2 August 2004
Accepted: 8 November 2004

Abstract

The iron Kα 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 Kα emission. It is shown that for gas columns comparable to the Thomson depth, the iron Kα yield is comparable to that observed provided that the electron energy is above ~600 keV and that the total kinetic luminosity of the beam is around ; 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 . Γ 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.