Deep observation of the giant radio lobes of Centaurus A with the Fermi Large Area Telescope

¹ Max-Planck-Institut für Kernphysik, PO Box 103980, 69029 Heidelberg, Germany
e-mail: bixian85@pmo.ac.cn
² Key Laboratory of Dark Matter and Space Astronomy, Purple Mountain Observatory, Chinese Academy of Sciences, 210008 Nanjing, PR China
³ University of Rome Sapienza and ICRANet, Dip. Fisica, p.le A. Moro 2, 00185 Rome, Italy
⁴ Institute for Physical Research, NAS of Armenia, 0203 Ashtarak-2, Armenia
⁵ Dublin Institute for Advanced Studies, 31 Fitzwilliam Place, Dublin 2, Ireland

Received: 22 December 2011
Accepted: 24 March 2012

Abstract

The detection of high-energy (HE) γ-ray emission up to ~3 GeV from the giant lobes of the radio galaxy Centaurus A has been recently reported by the Fermi-LAT Collaboration based on ten months of all-sky survey observations. A data set more than three times larger is used here to study the morphology and photon spectrum of the lobes with higher statistics. The larger data set results in the detection of HE γ-ray emission (up to ~6 GeV) from the lobes with a significance of more than 10 and 20σ for the north and the south lobe, respectively. Based on a detailed spatial analysis and comparison with the associated radio lobes, we report evidence for a substantial extension of the HE γ-ray emission beyond the WMAP radio image for the northern lobe of Cen A. We reconstructed the spectral energy distribution (SED) of the lobes using radio (WMAP) and Fermi-LAT data from the same integration region. The implications are discussed in the context of hadronic and time-dependent leptonic scenarios.