DISCOVERY OF GeV EMISSION FROM THE CIRCINUS GALAXY WITH THE FERMI LARGE AREA TELESCOPE

We report the discovery of gamma -ray emission from the Circinus galaxy using the Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope. Circinus is a nearby (~4 Mpc) starburst with a heavily obscured Seyfert-type active nucleus, bipolar radio lobes perpendicular to the spiral disk...

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Bibliographic Details
Published in:The Astrophysical journal 2013-12, Vol.779 (2), p.1-7
Main Authors: Hayashida, Masaaki, Stawarz, Lukasz, Cheung, Chi C, Bechtol, Keith, Madejski, Greg M, Ajello, Marco, Massaro, Francesco, Moskalenko, Igor V, Strong, Andrew, TIBALDO, LUIGI
Format: Article
Language:English
Subjects:
ASTRONOMY AND ASTROPHYSICS
Asymptotic properties
Emission
galaxies: active
galaxies: individual (Circinus)
galaxies: jets
galaxies: Seyfert
Lobes
Luminosity
Mathematical models
Photons
radiation mechanisms: non-thermal
Radio
Telescopes
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Summary:We report the discovery of gamma -ray emission from the Circinus galaxy using the Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope. Circinus is a nearby (~4 Mpc) starburst with a heavily obscured Seyfert-type active nucleus, bipolar radio lobes perpendicular to the spiral disk, and kpc-scale jet-like structures. Our analysis of 0.1-100 GeV events collected during 4 yr of LAT observations reveals a significant ([Asymptotically = to]7.3[sigma]) excess above the background. We find no indications of variability or spatial extension beyond the LAT point-spread function. A power-law model used to describe the 0.1-100 GeV gamma -ray spectrum yields a flux of (18.8 + or - 5.8) x 10 super(-9) photon cm super(-2) s super(-1) and photon index 2.19 + or - 0.12, corresponding to an isotropic gamma -ray luminosity of 3 x 10 super(40) erg s super(-1). This observed gamma -ray luminosity exceeds the luminosity expected from cosmic-ray interactions in the interstellar medium and inverse Compton radiation from the radio lobes. Thus, the origin of the GeV excess requires further investigation.
ISSN:0004-637X
1538-4357
DOI:10.1088/0004-637X/779/2/131