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Title: Discovery of GeV emission from the Circinus galaxy with the Fermi large area telescope

We report the discovery of γ-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 (≅ 7.3σ) 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 γ-ray spectrum yields a flux of (18.8 ± 5.8) × 10{sup –9} photon cm{sup –2} s{sup –1} and photon index 2.19 ± 0.12, corresponding to an isotropic γ-ray luminosity of 3 × 10{sup 40} erg s{sup –1}. This observed γ-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.
Authors:
 [1] ;  [2] ;  [3] ;  [4] ; ; ; ;  [5] ;  [6] ;  [7]
  1. Institute for Cosmic Ray Research, University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8582 (Japan)
  2. Institute of Space and Astronautical Science, JAXA, 3-1-1 Yoshinodai, Chuo-ku, Sagamihara, Kanagawa 252-5210 (Japan)
  3. Space Science Division, Naval Research Laboratory, Washington, DC 20375-5352 (United States)
  4. Kavli Institute for Cosmological Physics, University of Chicago, 5640 South Ellis Avenue, Chicago, IL 60637 (United States)
  5. Kavli Institute for Particle Astrophysics and Cosmology, SLAC National Accelerator Laboratory, Stanford University, 2575 Sand Hill Road M/S 29, Menlo Park, CA 94025 (United States)
  6. Space Sciences Laboratory, 7 Gauss Way, University of California, Berkeley, CA 94720-7450 (United States)
  7. Max-Planck Institut für extraterrestrische Physik, D-85748 Garching (Germany)
Publication Date:
OSTI Identifier:
22348408
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 779; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; COSMIC RADIATION; EMISSION; GALAXIES; GAMMA RADIATION; GEV RANGE; INTERACTIONS; LUMINOSITY; PHOTONS; SPACE; SPECTRA; TELESCOPES