2009 Fermi Symposium, Washington, D.C., Nov. 2-5 2 The calculations are specific to UHECR protons, but photodisintegration cross sections and approximations are also presented, including giant dipole resonance and nonresonant channels. Calculations of neutrino production from nuclear photodisintegration is briefly described. absorption processes are developed. The γγ pair pro- duction process, starting from the elementary γγ cross section, is applied to γ -ray attenuation by target pho- tons found in sources of high-energy radiation, and by target photons of the extragalactic background light. With this formalism in hand, the nature of high- energy radiation sources can be examined. This in- cludes tests for relativistic beaming such as the Comp- ton catastrophe, whereby the size scale of the source determined directly from radio observations or indi- rectly from the variability timescale of the radiation implies the level of the Compton-scattered X-ray and γ -ray flux if the radio-through-optical/UV emission is nonthermal synchrotron radiation. Minimum bulk Lorentz factors of relativistic outflows from γγ opacity arguments are derived. Moreover, minimum power re- quirements for synchrotron sources can be determined from equipartition arguments. Together, these argu- ments point toward relativistic outflows from highly compact sources, which almost certainly implicate black holes as the engines of the luminous radiation. For completeness, binary collision processes useful for calculating radiation signatures from cosmic-ray interactions are given, including the processes of sec- ondary nuclear production, bremsstrahlung, electron- positron annihilation, and Coulomb thermalization and knock-on electron processes. One of the important questions in high-energy as- trophysics is the method by which cosmic rays are accelerated to ≈ PeV energies by Galactic sources, and to ultra-high energies in extragalactic sources. The empirical data base that must be explained is extensive. This includes cosmic-ray anisotropy, ionic composition, and UHECR arrival directions. Features in the cosmic-ray spectrum include the knee at ≈ 3 PeV, the second knee at ≈ 4 × 10 17 eV, the ankle at ≈ 5 × 10 18 eV, and the cutoff at ≈ 6 × 10 19 eV, probably due to GZK effects. C. Particle Acceleration in Black-Hole Jets B. UHECRs from Blazars and GRBs Not even the highest energy cosmic rays point back to their sources due to deflections by the Galactic and intergalactic magnetic fields, which has made the birth of charged-particle astronomy difficult. In the meantime, the sources of the UHECRs can be es- tablished indirectly by identifying γ -ray signatures of hadronic acceleration, and directly by detecting neutrinos from their sources with, for example, the IceCube neutrino telescope. Discriminating leptonic from hadronic emission signatures in the absence of neutrino detection represents an important challenge in the Fermi era. Identification of features peculiar to hadronic processes, such as orphan flares in blazars, represents one approach, and the interpretation of un- usual temporal and spectral behaviors as indicated in delayed onset or extended radiation from GRBs, rep- resents another. A complete understanding of cosmic-ray origin re- quires that a mechanism for particle acceleration be identified. For this purpose, an introduction to Fermi acceleration is given, starting from the two distinct types of Fermi acceleration mechanisms due to shock acceleration resulting from particle diffusion across a shock front and convection downstream of the shock, and stochastic acceleration by plasma wave turbu- lence. Dimensional arguments leading to the Kraich- nan and Kolmogorov wave turbulence spectra are given. The Hillas criterion, whereby allowed sites for particle acceleration to energy E are restricted to those which satisfy the condition that the Larmor ra- dius is smaller than the size scale of the system, is presented. First-order and second-order Fermi acceleration mechanisms are developed to the point where max- imum particle energies in different astrophysical en- vironments can be derived. These maximum particle energies then implicate different classes of sources as plausible sites for cosmic-ray acceleration. Accelera- tion of cosmic rays by supernova remnant shocks re- mains the favored explanation for the sources which accelerate galactic cosmic rays, and may very well be demonstrated through Fermi measurements of the γ - ray spectra of supernova remnants. UHECR acceler- ation in the shocks and turbulent plasma formed in the relativistic jetted outflows of black-hole jets is the most likely explanation for their origin, compared to, for example, highly magnetized neutron stars or ac- cretion or merger shocks in clusters of galaxies. A treatment of photohadronic processes is given. This includes photomeson production from proton- photon interactions, ion-photon photopair (Bethe- Heitler) processes, and ion photodisintegration. To illustrate the use of the photohadronic physics pre- sented in the book, a calculation is made of the UHECR spectrum from the superposition of long- duration GRB sources whose rate density is assumed to follow various star-formation rate functions. (This calculation is far more difficult if UHECRs are acceler- ated by blazars, insofar as supermassive black holes in- crease in mass with time, their fueling is episodic, and they come from various classes of objects, for example, BL Lac objects and flat spectrum radio quasars.) The associated GZK neutrino spectrum is calculated for an assumed long-duration GRB origin of the UHECRs. eConf C091122