Very high energy gamma-ray-induced pair cascades in the radiation fields of dust tori of active galactic nuclei: Application to Cen A

Abstract

The growing number of extragalactic high-energy (HE, E > 100 MeV) and very high energy (VHE, E > 100 GeV) γ-ray sources that do not belong to the blazar class suggests that VHE γ-ray production may be a common property of most radio-loud active galactic nuclei. In a previous paper, we have investigated the signatures of Comptonsupported pair cascades initiated by VHE γ-ray absorption in monochromatic radiation fields, dominated by Lyα line emission from the broad-line region. In this paper, we investigate the interaction of nuclear VHE γ-rays with the thermal infrared radiation field from a circumnuclear dust torus. Our code follows the spatial development of the cascade in full three-dimensional geometry. We provide a model fit to the broadband spectral energy distribution (SED) of the dust-rich, γ-ray-loud radio galaxy Cen A and show that typical blazar-like jet parameters may be used to model the broadband SED, if one allows for an additional cascade contribution to the Fermi γ-ray emission. © 2011. The American Astronomical Society. All rights reserved. Printed in the U.S.A.