Active Galactic Nuclei as potential Sources of Ultra-High Energy Cosmic Rays

TL;DR

This paper reviews the role of Active Galactic Nuclei as potential sources of ultra-high-energy cosmic rays, discussing recent experimental findings, acceleration mechanisms, and promising astrophysical environments.

Contribution

It provides a comprehensive overview of possible UHECR acceleration sites and mechanisms in AGNs, highlighting the significance of recent observational data and theoretical models.

Findings

Fermi acceleration and shear acceleration are promising mechanisms.

Nearby FR I radio galaxies are suitable UHECR sources.

Recent instruments have advanced understanding of AGN-related UHECRs.

Abstract

Active Galactic Nuclei (AGNs) and their relativistic jets belong to the most promising class of ultra-high-energy cosmic ray (UHECR) accelerators. This compact review summarises basic experimental findings by recent instruments, and discusses possible interpretations and astrophysical constraints on source energetics. Particular attention is given to potential sites and mechanisms of UHECR acceleration in AGNs, including gap-type particle acceleration close to the black hole, as well as first-order Fermi acceleration at trans-relativistic shocks and stochastic shear particle acceleration in large-scale jets. It is argued that the last two represent the most promising mechanisms given our current understanding, and that nearby FR~I type radio galaxies provide a suitable environment for UHECR acceleration.