Cosmological Origin for Cosmic Rays above 10[TSUP]19[/TSUP] [CLC]e[/CLC]V

The cosmic-ray spectrum at 10 19 -10 20 eV, reported by the Fly's Eye and the AGASA experiments, is shown to be consistent with a cosmological distribution of sources of protons, with a power-law generation spectrum d ln N / d ln E = -2.3 ± 0.5 and energy production rate of 4.5 ± 1.5 × 10 44 ergs Mpc -3 yr -1 . The two events measured above 10 20 eV are not inconsistent with this model. Verifying the existence of a "blackbody cutoff," currently observed with low significance, would require ~30 observation years with existing experiments, but only ~1 year with the proposed ~5000 km 2 detectors. For a cosmological source distribution, no anisotropy is expected in the angular distribution of events with energies up to ~5 × 10 19 eV.