Annu. Rev. Astron. Astrophys. 1988. 36: 539-598 Copyright © 1998 by Annual Reviews. All rights reserved

6.3. Acceleration of Cosmic Rays in Extragalactic Radio Sources

Jets and cocoons have also been invoked to explain the question of production of ultra-high-energy cosmic rays (UHECRs), E > 4 × 10¹⁹ up to 3 × 10²⁰ eV, revealed by extensive air shower detectors (Norman et al 1996). The argument is that large-scale shocks produced inside a jet or by the expansion of the working surface and cocoon into the ambient plasma can accelerate already relativistic protons/ions to the maximum energies. The limiting upper energy cutoff is approximately E_max ZeB _s R_s, which yields (in typical units) for hot spots in jets (R_s ~ R_j, _s ~ _j)

(40)

and for overpressured cocoons

(41)

Therefore, hot spots and cocoons appear to be interesting candidates as UHECR sources. Also, the injection problem for ions is less severe than for electrons.