Ultra-high energy cosmic rays from radio galaxies revisited

Understand

A striking concentration of ultra-high energy cosmic ray (UHECR) events observed by the Pierre Auger Observatory around the direction of the nearby radio galaxy Centaurus A revives the idea that radio galaxies may be dominant sources of UHECR.

• In this paper, we give a brief overview about processes which may accelerate protons and nuclei in radio galaxies, and their relation to jet power, radio morphology and cosmic source density.
• We argue that, except for the most powerful FR-II radio galaxies, processes in radio lobes are unlikely to explain the origin of UHECR.
• However, Fermi acceleration of protons at internal shocks in the "blazarzone" of all radio galaxies, and their photohadronic conversion into neutrons, may lead to the ejection of "UHECR-beams", which remain collimated over several Mpc.