Nonthermal emission in the lobes of Fornax A

Abstract

Current measurements of the spectral energy distribution in radio, X-and-gamma-ray provide a sufficiently wide basis for determining basic properties of energetic electrons and protons in the extended lobes of the radio galaxy Fornax A. Of particular interest is establishing observationally, for the first time, the level of contribution of energetic protons to the extended emission observed by the Fermi satellite. Two recent studies concluded that the observed gamma-ray emission is unlikely to result from Compton scattering of energetic electrons off the optical radiation field in the lobes, and therefore that the emission originates from decays of neutral pions produced in interactions of energetic protons with protons in the lobe plasma, implying an uncomfortably high proton energy density. However, our exact calculation of the emission by energetic electrons in the magnetized lobe plasma leads to the conclusion that all the observed emission can, in fact, be accounted for by energetic electrons scattering off the ambient optical radiation field, whose energy density (which, based on recent observations, is dominated by emission from the central galaxy NGC 1316) we calculate to be higher than previously estimated.

arXiv commentCorrected typos; added reference; revised figure; result unchanged

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Cited by in corpus (6)

• Modeling the Extragalactic Background Light and the Cosmic Star Formation History
• Non-thermal emission in radio galaxy lobes: II. Centaurus A, Centaurus B, and NGC 6251
• Non-thermal emission in lobes of radio galaxies: III. 3C 98, Pictor A, DA 240, Cygnus A, 3C 326, and 3C 236
• The SRG/eROSITA all-sky survey: View of the Fornax galaxy cluster
• Non-thermal emission in the central starburst region of M82
• IGR J18249-3243: a new GeV-emitting FR II and the emerging population of high energy radio galaxies