Can gamma ray bursts produce the observed cosmic rays above 1020 eV?

It has been suggested that cosmological gamma-ray bursts (GRBs) can produce the observed flux and spectrum of cosmic rays at the highest energies. However, recent observations indicate that the redshift distribution of GRBs most likely follows that of the star formation rate in the universe, a rate which was much higher at redshifts 1.5-2 than it is today. Thus, most GRBs are at high redshifts. As a consequence, any cosmic rays emitted by these GRBs at energies above similar to 2-3 x 10(19) eV would be strongly attenuated by interactions with the 3 K background radiation. If one assumes rough equality between the energy released by GRBs in 10(-2) to 1 MeV photons, and that released in 10(20) eV cosmic rays, then less than 10% of the cosmic rays observed above 10(20) eV can be accounted for by GRBs. (C) 2000 Elsevier Science B.V. All rights reserved.