Multiwavelength modeling of TeV AGN observed by HESS

TL;DR

This paper reviews the capabilities of the H.E.S.S. gamma-ray telescope array in observing extragalactic TeV sources, highlighting recent discoveries, variability patterns, and the implications for understanding black hole regions, jet emissions, and the extragalactic background light.

Contribution

It provides a comprehensive overview of H.E.S.S. observations of extragalactic TeV sources, including new detections and insights into their emission mechanisms and background light.

Findings

Detection of gamma-ray emission from M87, the first non-blazar extragalactic source at TeV energies.

Observation of diverse temporal behaviors among blazars, indicating complex emission processes.

Indirect constraints on the extragalactic background light from gamma-ray observations.

Abstract

The High Energy Stereoscopic System (H.E.S.S.) experiment, a ground-based gamma-ray Cherenkov telescope array located in Namibia, has now detected many extragalactic objects, which redshifts range from z=0.00183 up to z=0.2, possibly more. With the increasing performances of Cherenkov telescopes, it now becomes possible to probe these objects at small timescales in gamma-ray, allowing the study of regions thought to be very close to the central supermassive black holes. Furthermore, H.E.S.S. has confirmed a gamma-ray emission from M87, which is thus the first extragalactic source seen at the TeV range that is not a blazar. Among blazars, TeV BL Lacs are the most challenging objects to test the jet emission models and to shed light on particle acceleration mechanisms. The study of blazars with H.E.S.S. also revealed various temporal behaviors among them. Some objects presents a highly variable X-ray flux with small variation of the gamma-ray, while others show the inverse behavior. The interpretation of such differences is puzzling. Observations at very high energies also bring indirect measurements of the infrared extragalactic background light (EBL). The interpretation of gamma-ray emission of radiogalaxies such as M87 in terms of misaligned blazars and the understanding of the properties of the EBL represent new challenges brought by H.E.S.S. observations of extragalactic sources.