Data di Pubblicazione:
2013
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.
Tipologia CRIS:
03A-Articolo su Rivista
Keywords:
galaxies: active , galaxies: individual (Circinus) , galaxies: jets , galaxies: Seyfert , radiation mechanisms: non-thermal
Elenco autori:
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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