Gamma-ray fluxes from the core emission of Centaurus A: A puzzle solved

Abstract

A high-energy component in the radio galaxy Centaurus A was reported after analysing four years of Fermi data. The spectrum of this component is described by means of a broken power law with a break energy of 4 GeV and, below and above spectral indices of α1 = 2.74 ± 0.03 and α2 = 2.09 ± 0.20, respectively. Also a faint γ-ray flux at TeV energies was detected by High Energy Stereoscopic System. In this paper, we show that the spectrum at GeV-TeV energies is described through synchrotron self-Compton emission up to a few GeV (~4 GeV) and π0 decay products up to TeV energies, although the emission of synchrotron radiation by muons could contribute to the spectrum at GeV energies, if they are rapidly accelerated. Muons and π0s are generated in the interactions of accelerated protons with two populations of seed photons which were reported by Compton Gamma-Ray Observatory: one population at intermediate-state emission with energy peak of 0.15 MeV and another at low-state emission with energy peak of 0.59 MeV. In addition, we show that the reported observations of ultrahigh-energy cosmic rays and non-high-energy neutrino detection around Centaurus A can be explained through these interactions, assuming that proton spectrum is extended up to ultrahigh energies. © 2014 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.