Gamma-Rays from Radio Galaxies: Fermi-Lat Observations

TL;DR

This paper reviews Fermi-LAT observations of gamma-ray emissions from radio galaxies, highlighting differences between low and high power sources and proposing beaming and jet structure as key factors.

Contribution

It provides a comprehensive analysis of gamma-ray properties of misaligned AGNs and suggests explanations for the detection rate differences based on jet structure.

Findings

Most gamma-ray detected AGNs are nearby low-power radio galaxies.

High-power radio sources with GeV emission are rare and not solely due to redshift.

Beaming and jet structure differences likely explain detection discrepancies.

Abstract

We review the high energy properties of Misaligned AGNs associated with gamma-ray sources detected by Fermi in 24 months of survey. Most of them are nearby emission low power radio galaxies (i.e FRIs) which probably have structured jets. On the contrary, high power radio sources (i.e FRIIs) with GeV emission are rare. The small number of FRIIs does not seem to be related to their higher redshifts. Assuming proportionality between the radio core flux and the gamma-ray flux, several of them are expected to be bright enough to be detected above 100 MeV in spite of their distance. We suggest that beaming/jet structural differences are responsible for the detection rate discrepancy observed between FRIs and FRIIs.