How many Ultra High Energy Cosmic Rays could we expect from Centaurus A?

TL;DR

This study models the spectrum of Centaurus A to estimate the expected ultra high energy cosmic rays and neutrino signals, finding that proton-proton interactions align with observations and could inform future neutrino detection efforts.

Contribution

It introduces a combined leptonic and hadronic modeling approach for Centaurus A's spectrum, linking cosmic ray predictions with observational data and neutrino signal estimates.

Findings

Proton-proton interactions produce cosmic ray flux consistent with Pierre Auger data.

Proton-photon interactions imply an unrealistically high cosmic ray luminosity.

Neutrino flux estimates suggest potential detectability with km$^3$ neutrino telescopes.

Abstract

The Pierre Auger Observatory has associated a few ultra high energy cosmic rays with the direction of Centaurus A. This source has been deeply studied in radio, infrared, X-ray and $\gamma$-rays (MeV-TeV) because it is the nearest radio-loud active galactic nuclei. Its spectral energy distribution or spectrum shows two main peaks, the low energy peak, at an energy of $10^{-2}$ eV, and the high energy peak, at about 150 keV. There is also a faint very high energy (E $\geq$ 100 GeV) $\gamma$-ray emission fully detected by the High Energy Stereoscopic System experiment. In this work we describe the entire spectrum, the two main peaks with a Synchrotron/Self-Synchrotron Compton model and, the Very High Energy emission with a hadronic model. We consider p$\gamma$ and $pp$ interactions. For the p$\gamma$ interaction, we assume that the target photons are those produced at 150 keV in the leptonic processes. On the other hand, for the pp interaction we consider as targets the thermal particle densities in the lobes. Requiring a satisfactory description of the spectra at very high energies with p$\gamma$ interaction we obtain an excessive luminosity in ultra high energy cosmic rays (even exceeding the Eddington luminosity). However, when considering pp interaction to describe the $\gamma$-spectrum, the obtained number of ultra high energy cosmic rays are in agreement with Pierre Auger observations. Moreover, we calculate the possible neutrino signal from pp interactions on a Km$^3 $ neutrino telescope using Monte Carlo simulations.