Fermi-Large Area Telescope Detection of Very High Energy (>100 GeV) Emission from Misaligned Jetted Active Galactic Nuclei

TL;DR

This study detects very-high-energy gamma-ray emissions from misaligned jetted AGN using 16 years of Fermi-LAT data, expanding the known sample and challenging existing emission models.

Contribution

It systematically identifies new VHE-emitting radio galaxies and candidates, including first-time detections, using extensive Fermi-LAT data analysis.

Findings

12 sources detected at >4σ confidence level

Two radio galaxies detected in VHE band for the first time

Three promising VHE candidates identified

Abstract

The detection of very-high-energy (VHE; $>$100 GeV) $\gamma$-ray radiation from misaligned jetted Active Galactic Nuclei (AGN) challenges the emission models that primarily explain VHE emissions from beamed AGN, i.e., blazars. Using over 16 years of \textit{Fermi}-Large Area Telescope (\textit{Fermi}-LAT) Pass 8 data in the energy range 0.1$-$2 TeV, we systematically explore the VHE emission from a recently published sample of 160 radio galaxies. We identify 12 sources detected at $>4\sigma$ confidence level (test statistic or TS$>$16), including nine with TS$>$25 and two Fanaroff-Riley type II objects. This detected sample includes seven out of eight previously known VHE objects. Two radio galaxies are detected in the VHE band for the first time, and we identify three promising candidates with 16$<$TS$<$25. Additionally, 13 objects are identified as candidate VHE emitters with at least one VHE photon detected with the \textit{Fermi}-LAT. These findings expand the sample of known VHE-emitting radio galaxies, whose multiwavelength follow-up observations can help provide insights into the emission mechanisms, jet physics, and the contribution of misaligned AGN to the extragalactic $\gamma$-ray background.