Active Galaxies Studied with the H.E.S.S. Observatory

TL;DR

This paper reviews the status of active galactic nuclei studies using the H.E.S.S. observatory, focusing on emission mechanisms, background light constraints, and the gamma-ray AGN population.

Contribution

It provides a comprehensive overview of recent findings on VHE gamma-ray emission from various AGN types and their implications for astrophysics.

Findings

Constraints on blazar emission zones and energy dissipation processes.

Limits on extragalactic background light from blazar observations.

Insights into the gamma-ray loud AGN population from multi-wavelength data.

Abstract

X-ray selected BL Lac objects dominate the population of extragalactic sources detected in the very high energy (VHE; photon energies >100GeV) gamma-ray regime with ground-based Cherenkov Telescopes. These are not the only extragalactic VHE emitters, however, since also other types of active galactic nuclei (AGN) have recently been established as VHE sources as well. They include radio galaxies, optically-selected BL Lacs, and Flat-Spectrum Radio Quasars. Here we review the current status of the ongoing AGN studies with the H.E.S.S. instrument, concentrating on the following main three topics: (i) constraints on the structure of the blazar emitting zone, and on the energy dissipation processes involved in the production of the high-energy emission in AGN, enabled by detailed timing and spectral analysis of the H.E.S.S. data; (ii) constraints on the extragalactic background light (EBL) using H.E.S.S. observations of blazars, and (iii) the phenomenological picture of the gamma-ray loud AGN population emerging from combined VHE and multi-wavelength observations of different classes of active galaxies.