|Annu. Rev. Astron. Astrophys. 1988. 36:
Copyright © 1998 by . 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 Emax ZeB s Rs, which yields (in typical units) for hot spots in jets (Rs ~ Rj, s ~ j)
and for overpressured cocoons
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.