Very high-energy gamma-ray signature of ultrahigh-energy cosmic-ray acceleration in Centaurus A

TL;DR

This paper models gamma-ray emission from Centaurus A, linking it to ultrahigh-energy cosmic-ray acceleration, and demonstrates that hadronic processes can explain observed very high-energy gamma-ray data.

Contribution

It introduces combined leptonic and hadronic models to explain gamma-ray observations and UHECR correlations from Centaurus A.

Findings

Hadronic emission can account for VHE gamma-ray data.

The cosmic ray luminosity matches UHECR observations.

Two-zone emission models explain GeV to TeV gamma-ray spectra.

Abstract

The association of at least a dozen ultrahigh-energy cosmic-ray (UHECR) events with energy $\gtrsim 55$ EeV detected by the Pierre Auger Observatory (PAO) from the direction of Centaurus-A, the nearest radio galaxy, supports the scenario of UHECR acceleration in the jets of radio galaxies. In this work, we model radio to very high energy (VHE,$\gtrsim 100$ \rm GeV) $\gamma$-ray emission from Cen A, including GeV hardness detected by Fermi-LAT and TeV emission detected by HESS. We consider two scenarios: (i) Two zone synchrotron self-Compton (SSC) and external-Compton (EC) models, (ii) Two zone SSC, EC and photo-hadronic emission from cosmic ray interactions. The GeV hardness observed by Fermi-LAT can be explained using these two scenarios, where zone 2 EC emission is very important. Hadronic emission in scenario (ii) can explain VHE data with the same spectral slope as obtained through fitting UHECRs from Cen A. The peak luminosity in cosmic ray proton at 1 TeV, to explain the VHE $\gamma$-ray data is $\approx 2.5 \times 10^{46}$ erg/s. The bolometric luminosity in cosmic ray protons is consistent with the luminosity required to explain the origin of 13 UHECR signal events that are correlated with Cen A.