Letter to the Editor

Very high-energy γ-ray emission from IC 310

¹ ISDC Data Centre for Astrophysics, Ch. d'Ecogia 16, 1290 Versoix, Switzerland e-mail: andrii.neronov@unige.ch
² APC, 10 rue Alice Domon et Leonie Duquet, 75205 Paris Cedex 13, France
³ Institute for Nuclear Research RAS, 60th October Anniversary prosp. 7a, Moscow 117312, Russia

Received: 25 March 2010
Accepted: 14 July 2010

Abstract

Context. We search for persistent extragalactic sources of γ-ray s with energies above 100 GeV with the Fermi telescope.

Aims. We construct a systematic survey of the extragalactic γ-ray sky at energies above 100 GeV. Such a survey has not been done before by the ground-based Cherenkov γ-ray telescopes, which have, contrary to Fermi, a narrow field of view.

Methods. We study a map of arrival directions of the highest energy photons detected by Fermi at Galactic latitudes |b| > 10° and search for significant point-source-like excesses above the diffuse Galactic and extragalactic γ-ray backgrounds. We identify eight significant point-source-like excesses in this map.

Results. Seven of the eight sources are known TeV blazars. The previously unknown source is identified with the galaxy IC 310, which is situated in Perseus cluster of galaxies. The source is detected with a significance 6σ above 30 GeV. We identify two possible scenarii for γ-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 γ-ray photons could be produced at the bow shock that is formed as a result of the fast motion of the galaxy through the intracluster medium. The two models could be distinguished through studying of the γ-ray signal variability.