# Cosmic ray acceleration to ultrahigh energy in radio galaxies

## TL;DR

This paper reviews how radio galaxy shocks can accelerate cosmic rays to ultrahigh energies and proposes that giant radio galaxies serve as reservoirs for these particles, potentially explaining observed cosmic ray anisotropies.

## Contribution

It introduces a model where radio galaxy backflows accelerate UHECRs and act as reservoirs, linking radio galaxies to observed cosmic ray anisotropies.

## Key findings

- Radio galaxy shocks meet acceleration requirements for 10-100 EeV cosmic rays.
- Giant-lobed radio galaxies can act as UHECR reservoirs during past active episodes.
- Radio galaxies like Centaurus A may explain anisotropies observed by Pierre Auger Observatory.

## Abstract

The origin of ultrahigh energy cosmic rays (UHECRs) is an open question. In this proceeding, we first review the general physical requirements that a source must meet for acceleration to 10-100 EeV, including the consideration that the shock is not highly relativistic. We show that shocks in the backflows of radio galaxies can meet these requirements. We discuss a model in which giant-lobed radio galaxies such as Centaurus A and Fornax A act as slowly-leaking UHECR reservoirs, with the UHECRs being accelerated during a more powerful past episode. We also show that Centaurus A, Fornax A and other radio galaxies may explain the observed anisotropies in data from the Pierre Auger Observatory, before examining some of the difficulties in associating UHECR anisotropies with astrophysical sources.