High energy radiation from Centaurus A

Abstract

We calculate for the nearest active galactic nucleus (AGN), Centaurus A, the flux of high energy cosmic rays and of accompanying secondary photons and neutrinos expected from hadronic interactions in the source. We use as two basic models for the generation of ultrahigh energy cosmic rays (UHECR) shock acceleration in the radio jet and acceleration in the regular electromagnetic field close to the core of the AGN. While scattering on photons dominates in scenarios with acceleration close to the core, scattering on gas becomes more important if acceleration takes place along the jet. Normalizing the UHECR flux from Centaurus A to the observations of the Auger experiment, the neutrino flux may be marginally observable in a 1 km$^3$ neutrino telescope, if a steep UHECR flux $\d N/\d E\propto E^{-α}$ with $α=2.7$ extends down to $10^{17}$ eV. The associated photon flux is close to or exceeds the observational data of atmospheric Cherenkov and $γ$-ray telescopes for $α\gsim 2$. In particular, we find that already present data favour either a softer UHECR injection spectrum than $α=2.7$ for Centaurus A or a lower UHECR flux than expected from the normalization to the Auger observations.