Sub-parsec and parsec VHE emission from the core of LLAGNs

Abstract

Radio galaxies with misaligned outflows emit radiation in the very-high-energy regime (VHE; >100 GeV). The standard synchrotron self-Compton scenario is not able to explain this emission. Alternative pictures to explain the production of VHE fluxes could be found in hadronic emission models. Here we consider cosmic-ray (CR) acceleration by magnetic reconnection in the immediate vicinity of the black hole engine and calculate the resulting hadronic emission at sub-parsec, and parsec scales. The former takes place basically due to the interaction of CRs with the inner accretion flow. The latter is due to CRs that escape their acceleration zone and diffuse within the dense interstellar medium at parsec scales. We constrain the power of CR injection by the available magnetic reconnection power of the system and apply this hadronic multi-scale emission scenario to model the VHE spectral energy distribution (SED) from core of Centaurus A. We find that the required CR power needed to explain the VHE cannot be provided only by magnetic reconnection power. On the other hand, CRs produced by magnetic reconnection together with CR injected by supernovae (SNe) during the past $10^4$ yr could explain most of the VHE SED assuming a rate of 10$^{-2}$ yr$^ {-1}$ SN events within the circumnuclear disc of this radiogalaxy.