High energy radiation from Centaurus A

TL;DR

This paper models high energy cosmic ray production in Centaurus A, predicting associated neutrino and photon fluxes, and compares these with observational data to constrain the source's acceleration mechanisms and spectrum.

Contribution

It introduces two models for UHECR acceleration in Centaurus A and assesses their implications for observable neutrino and photon fluxes, providing constraints based on current data.

Findings

Neutrino flux from Centaurus A may be detectable with km$^3$ neutrino telescopes.

Photon flux predictions are consistent with current gamma-ray observations for certain spectral indices.

Current data favor a softer UHECR spectrum or lower flux than the initial model predictions.

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 $\d N/\d E\propto E^{-\alpha}$ with $\alpha=2.7$ extends down to $10^{17}$ eV. The associated photon flux is close to or exceeds the observational data of atmospheric Cherenkov and $\gamma$-ray telescopes for $\alpha\gsim 2$. In particular, we find that already present data favour either a softer UHECR injection spectrum than $\alpha=2.7$ for Centaurus A or a lower UHECR flux than expected from the normalization to the Auger observations.