On the origin of very high energy gamma-rays from radio galaxies

TL;DR

This paper reviews the recent discoveries of very high energy gamma-ray emissions from radio galaxies, focusing on their characteristics and the theoretical models explaining their variable emission, especially in M87.

Contribution

It provides a summary of observed VHE gamma-ray emissions from radio galaxies and discusses recent theoretical advances, particularly in understanding M87's variable emission.

Findings

Radio galaxies are confirmed as a new class of VHE gamma-ray sources.

Magnetospheric particle acceleration models are relevant for explaining M87's emission.

Recent theoretical progress enhances understanding of non-thermal processes in AGN.

Abstract

Radio galaxies have emerged as a new gamma-ray emitting source class on the extragalactic sky. With their jets misaligned, i.e. not directly pointing towards us, they offer a unique tool to probe some of the fundamental (and otherwise hidden) non-thermal processes in AGN. This contribution briefly summarizes the observed characteristics of the four radio galaxies detected so far at very high energies (VHE). Given its prominence, particular attention is given to the origin of the variable VHE emission in M87. We discuss some of the theoretical progress achieved for this source within recent years highlighting, amongst others, the relevance of magnetospheric particle acceleration and emission models.