One-zone synchrotron self-Compton model for the core emission of Centaurus A revisited

Abstract

Aims: We investigate the role of the second synchrotron self-Compton (SSC) photon generation to the multiwavelength emission from the compact regions of sources that are characterized as misaligned blazars. For this, we focus on the nearest high-energy emitting radio galaxy Centaurus A and we revisit the one-zone SSC model for its core emission. Methods: We have calculated analytically the peak luminosities of the first and second SSC components by, first, deriving the steady-state electron distribution in the presence of synchrotron and SSC cooling and, then, by using appropriate expressions for the positions of the spectral peaks. We have also tested our analytical results against those derived from a numerical code where the full emissivities and cross-sections were used. Results: We show that the one-zone SSC model cannot account for the core emission of Centaurus A above a few GeV, where the peak of the second SSC component appears. We, thus, propose an alternative explanation for the origin of the high energy ($\gtrsim 0.4$ GeV) and TeV emission, where these are attributed to the radiation emitted by a relativistic proton component through photohadronic interactions with the photons produced by the primary leptonic component. We show that the required proton luminosities are not extremely high, e.g. $\sim 10^{43}$ erg/s, provided that the injection spectra are modelled by a power-law with a high value of the lower energy cutoff. Finally, we find that the contribution of the core emitting region of Cen A to the observed neutrino and ultra-high energy cosmic-ray fluxes is negligible.