Which radio galaxies can make the highest-energy cosmic rays?

Abstract

Numerous authors have suggested that the ultra-high energy cosmic rays (UHECR) detected by the Pierre Auger Observatory and other cosmic-ray telescopes may be accelerated in the nuclei, jets or lobes of radio galaxies. Here I focus on stochastic acceleration in the lobes. I show that the requirement that they accelerate protons to the highest observed energies places constraints on the observable properties of radio lobes that are satisfied by a relatively small number of objects within the Greisen-Zat'sepin-Kuzmin (GZK) cutoff; if UHECR are protons and are accelerated within radio lobes, their sources are probably already known and catalogued radio galaxies. I show that lobe acceleration also implies a (charge-dependent) upper energy limit on the UHECR that can be produced in this way; if lobes are the dominant accelerators in the local universe and if UHECR are predominantly protons, we are unlikely to see cosmic rays much higher in energy than those we have already observed. I comment on the viability of the stochastic acceleration mechanism and the likely composition of cosmic rays accelerated in this way, based on our current understanding of the contents of the large-scale lobes of radio galaxies, and finally discuss the implications of stochastic lobe acceleration for the future of cosmic ray astronomy.

7 pages, 2 figures. Accepted by MNRAS. Updated version fixes typos and adds a couple of missing references; no substantive change

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Cited by in corpus (16)

• Origin of Cosmic Rays
• Ultra-high energy cosmic rays from shocks in the lobes of powerful radio galaxies
• Mass entrainment and turbulence-driven acceleration of ultra-high energy cosmic rays in Centaurus A
• Fornax A, Centaurus A and other radio galaxies as sources of ultra-high energy cosmic rays
• Fueling lobes of radio galaxies: statistical particle acceleration and the extragalactic gamma-ray background
• Broadband radio polarimetry of Fornax A, I: Depolarized patches generated by advected thermal material from NGC 1316
• Neutrino, $\gamma$-ray and cosmic ray fluxes from the core of the closest radio galaxies
• Active Galactic Nuclei as potential Sources of Ultra-High Energy Cosmic Rays
• Dynamical Modelling and Emission Signatures of a Candidate Dual AGN with Precessing Radio Jets
• Cosmic Ray Acceleration in Hydromagnetic Flux Tubes
• Cosmic ray acceleration to ultrahigh energy in radio galaxies
• A Simulation Study of Ultra-relativistic Jets -- II. Structures and Dynamics of FR-II Jets
• On the origin and acceleration of cosmic rays: Cooling flow clusters and AGN hosts
• High Energy Neutrinos and Cosmic Rays
• Echoes of the past: ultra-high energy cosmic rays accelerated by radio galaxies, scattered by starburst galaxies
• On the extragalactic jet asymmetry and composition, and the production of high energy cosmic rays