Radio Galaxies at TeV Energies

Unlike blazars, radio galaxies have jets that are misaligned relative to our line-of-sight. This misaligned geometry provides us with a unique view of both the jet and super massive black hole. To date, four radio galaxies have been detected at TeV energies with an additional two active galactic nuclei shown to exhibit both radio galaxy and BL Lac-type properties. TeV observations of radio galaxies have revealed these objects to be fascinating, displaying ultra-fast variability and often relatively hard spectral energy distributions. This work aims to provide a review of the current state of radio galaxy observations within the context of very-high-energy γ-ray astronomy, while also highlighting that radio galaxies are excellent targets for multi-wavelength observations. A number of motivations for the continued study of radio galaxies are provided, and these are discussed with a focus on the key observational results, including implications for future observations with next-generation instruments soon to be operational.

Radio Galaxies at VHE Energies

Radio Galaxies have by now emerged as a new γ-ray emitting source class on the extragalactic sky. Given their remarkable observed characteristics, such as unusual gamma-ray spectra or ultrafast VHE variability, they represent unique examples to probe the nature and physics of active galactic nuclei (AGN) in general. This review provides a compact summary of their observed characteristics at very high γ-ray energies (VHE; greater than 100 GeV) along with a discussion of their possible physics implications. A particular focus is given to a concise overview of fundamental concepts concerning the origin of variable VHE emission, including recent developments in black hole gap physics.