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. Thus, the origin of the GeV excess requires further investigation.

Discovery of GeV Emission from the Circinus Galaxy with the Fermi Large Area Telescope

MASSARO, Francesco;
2013-01-01

Abstract

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. Thus, the origin of the GeV excess requires further investigation.
2013
779
131
137
http://iopscience.iop.org/article/10.1088/0004-637X/779/2/131/pdf
https://arxiv.org/abs/1310.1913
galaxies: active , galaxies: individual (Circinus) , galaxies: jets , galaxies: Seyfert , radiation mechanisms: non-thermal
Masaaki Hayashida;Łukasz Stawarz;Chi C. Cheung;Keith Bechtol;Greg M. Madejski;Marco Ajello;Francesco Massaro;Igor V. Moskalenko;Andrew Strong;Luigi Tibaldo
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/2318/154198
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