VHE Gamma-Ray Induced Pair Cascades in the Radiation Fields of Dust Tori of AGN: Application to Cen A

TL;DR

This paper models how VHE gamma-rays interact with dust torus radiation in AGN, producing pair cascades that influence gamma-ray emission, and applies this to explain Cen A's broadband spectrum.

Contribution

It introduces a 3D cascade model for VHE gamma-ray interactions with dust torus radiation in AGN, extending previous work on Ly-alpha fields.

Findings

The model fits Cen A's broadband SED including cascade contributions.

Blazar-like jet parameters can explain gamma-ray emission with cascade effects.

Cascade processes significantly impact the gamma-ray spectra of dust-rich AGN.

Abstract

The growing number of extragalactic high-energy (HE, E > 100 MeV) and very-high-energy (VHE, E > 100 GeV) gamma-ray sources that do not belong to the blazar class suggests that VHE gamma-ray production may be a common property of most radio-loud Active Galactic Nuclei (AGN). In a previous paper, we have investigated the signatures of Compton-supported pair cascades initiated by VHE gamma-ray absorption in monochromatic radiation fields, dominated by Ly-alpha line emission from the Broad Line Region. In this paper, we investigate the interaction of nuclear VHE gamma-rays with the thermal infrared radiation field from a circumnuclear dust torus. Our code follows the spatial development of the cascade in full 3-dimensional geometry. We provide a model fit to the broadband SED of the dust-rich, gamma-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 gamma-ray emission.