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Title: Discovery of GeV emission from the Circinus galaxy with the Fermi Large Area Telescope [Discovery of GeV emission from the Circinus galaxy with the Fermi-LAT]

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 –9 photon cm –2 s –1 and photon index 2.19 ± 0.12, corresponding to an isotropic γ-ray luminosity of 3 × 10 40 erg s –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. Furthermore, the origin of the GeV excess requires further investigation.
Authors:
 [1] ;  [2] ;  [3] ;  [4] ;  [5] ;  [6] ;  [5] ;  [5] ;  [7] ;  [5]
  1. Univ. of Tokyo, Chiba (Japan); Stanford Univ., Stanford, CA (United States). SLAC National Accelerator Lab.
  2. Institute of Space and Astronomical Science, Kanagawa (Japan); Jagiellonian Univ., Krakow (Poland)
  3. Naval Research Lab., Washington, D.C. (United States)
  4. Univ. of Chicago, Chicago, IL (United States)
  5. Stanford, CA (United States). SLAC National Accelerator Lab
  6. Univ. of California, Berkeley, CA (United States)
  7. Max-Planck Institut fur extraterrestrische Physik, Garching (Germany)
Publication Date:
Grant/Contract Number:
AC02-76SF00515
Type:
Accepted Manuscript
Journal Name:
Astrophysical Journal
Additional Journal Information:
Journal Volume: 779; Journal Issue: 2; Journal ID: ISSN 0004-637X
Publisher:
Institute of Physics (IOP)
Research Org:
SLAC National Accelerator Lab., Menlo Park, CA (United States)
Sponsoring Org:
USDOE
Country of Publication:
United States
Language:
English
Subject:
79 ASTRONOMY AND ASTROPHYSICS; galaxies: active; galaxies: individual (Circinus); galaxies: jets; galaxies: Seyfert; radiation mechanisms: non-thermal
OSTI Identifier:
1356548

Hayashida, Masaaki, Stawarz, Łukasz, Cheung, Chi C., Bechtol, Keith, Madejski, Greg M., Ajello, Marco, Massaro, Francesco, Moskalenko, Igor V., Strong, Andrew, and Tibaldo, Luigi. Discovery of GeV emission from the Circinus galaxy with the Fermi Large Area Telescope [Discovery of GeV emission from the Circinus galaxy with the Fermi-LAT]. United States: N. p., Web. doi:10.1088/0004-637X/779/2/131.
Hayashida, Masaaki, Stawarz, Łukasz, Cheung, Chi C., Bechtol, Keith, Madejski, Greg M., Ajello, Marco, Massaro, Francesco, Moskalenko, Igor V., Strong, Andrew, & Tibaldo, Luigi. Discovery of GeV emission from the Circinus galaxy with the Fermi Large Area Telescope [Discovery of GeV emission from the Circinus galaxy with the Fermi-LAT]. United States. doi:10.1088/0004-637X/779/2/131.
Hayashida, Masaaki, Stawarz, Łukasz, Cheung, Chi C., Bechtol, Keith, Madejski, Greg M., Ajello, Marco, Massaro, Francesco, Moskalenko, Igor V., Strong, Andrew, and Tibaldo, Luigi. 2013. "Discovery of GeV emission from the Circinus galaxy with the Fermi Large Area Telescope [Discovery of GeV emission from the Circinus galaxy with the Fermi-LAT]". United States. doi:10.1088/0004-637X/779/2/131. https://www.osti.gov/servlets/purl/1356548.
@article{osti_1356548,
title = {Discovery of GeV emission from the Circinus galaxy with the Fermi Large Area Telescope [Discovery of GeV emission from the Circinus galaxy with the Fermi-LAT]},
author = {Hayashida, Masaaki and Stawarz, Łukasz and Cheung, Chi C. and Bechtol, Keith and Madejski, Greg M. and Ajello, Marco and Massaro, Francesco and Moskalenko, Igor V. and Strong, Andrew and Tibaldo, Luigi},
abstractNote = {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) × 10–9 photon cm–2 s–1 and photon index 2.19 ± 0.12, corresponding to an isotropic γ-ray luminosity of 3 × 1040 erg s–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. Furthermore, the origin of the GeV excess requires further investigation.},
doi = {10.1088/0004-637X/779/2/131},
journal = {Astrophysical Journal},
number = 2,
volume = 779,
place = {United States},
year = {2013},
month = {12}
}