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The discoveries of the GZK cutoff with the HiRes and Auger Observatories andthe discovery by Auger of clustering of >~60 EeV ultra-high energy cosmic rays(UHECRs) towards nearby <~75 Mpc) AGNs along the supergalactic planeestablishes the astrophysical origin of the UHECRs. The likely sources of theUHECRs are gamma-ray bursts and radio-loud AGNs because: (1) they areextragalactic; (2) they are sufficiently powerful; (3) acceleration toultra-high energies can be achieved in their relativistic ejecta; (4) anomalousX-ray and gamma-ray features can be explained by nonthermal hadron accelerationin relativistic blast waves; and (5) sources reside within the GZK radius. Twoarguments for acceleration to UHE are presented, and limits on UHECR ionacceleration are set. UHECR ions are shown to be able to survive withoutphotodisintegrating while passing through the AGN scattered radiation field,even if launched deep in the broad line region. UHECR injection throughoutcosmic time fits the measured energy spectrum of UHECRs, at least for protons.Local UHECR proton and ion interaction and energy-loss mean free paths arecalculated using an empirical fit to the extragalactic background light (EBL)at IR and optical energies. Minimum intergalactic magnetic (IGM) fields ~1e-11G are derived from clustering assuming specific source origins, e.g., Cen A,nearby AGNs, or GRBs for the super-GZK CRs seen with Auger. Besides distinctcosmic-ray induced gamma-ray signatures that should be observed with the Gammaray Large Area Space Telescope (GLAST), source and GZK neutrino detections andthe arrival distribution of UHECR in direction and time can finally decide thesources of cosmic rays at the highest energies.

On Gamma Ray Burst and Blazar AGN Origins of the Ultra-High Energy Cosmic Rays in Light of First Results from Auger