Very high-energy gamma-ray emission from IC 310

TL;DR

This paper reports the discovery of very high-energy gamma-ray emission from the radio galaxy IC 310, identified through a systematic survey of Fermi telescope data, revealing new insights into extragalactic gamma-ray sources.

Contribution

It presents the first systematic survey of >100 GeV gamma-ray sky using Fermi data and identifies IC 310 as a new gamma-ray source with potential emission mechanisms.

Findings

IC 310 is a new gamma-ray source detected at 6 sigma significance.

Seven known TeV blazars were identified in the survey.

Two possible emission scenarios for IC 310 are proposed.

Abstract

We construct a systematic survey of extragalactic \gamma-ray sky at the energies above 100 GeV using the data of Fermi telescope. Such survey has not been previously done by the ground-based Cherenkov gamma-ray telescopes which have, contrary to Fermi, narrow field of view. We study a map of arrival directions of the highest energy photons detected by Fermi at Galactic latitudes |b| > 10 degrees and search for significant point source like excesses above the diffuse Galactic and extragalactic \gamma-ray backgrounds. We identify eight significant point source like excesses in this map. Seven of the eight sources are known TeV blazars. The previously unknown source is identified with a head-tail radio galaxy IC 310, situated in Perseus cluster of galaxies. The source is detected with significance 6 sigma above 30 GeV. We identify two possible scenaria for gamma-ray emission from this source. One possibility is that emission originates from the base of relativistic outflow from the active nucleus, as in the BL Lacs and FR I type radio galaxies. Otherwise gamma-ray photons could be produced at the bow shock formed in result of fast motion of the galaxy through the intracluster medium. The two models could be distinguished via the study of variability of the \gamma-ray signal.