ULTRAHIGH-ENERGY COSMIC-RAYS - POSSIBLE ORIGIN AND SPECTRUM

The complicated shape of the cosmic ray spectrum recorded by giant arr ays in the energy range 10(17)-10(20) eV is analyzed. It is shown that in the energy region similar to 10(18)-10(19) eV the spectrum probabl y coincides with the injection spectrum whose exponent is equal approx imately to 3.2-3.3. The flatter component in the energy region (3.2-5. 0)x10(19) eV is due to braking of extragalactic protons on primordial photons (the cosmic background radiation). At energies exceeding 3.2x1 0(19) eV the spectrum does not have a blackbody cutoff. The possibilit y of determining the distances at which cosmic rays originate and inve stigating the evolution of their sources on the basis of ultrahigh-ene rgy cosmic ray data is discussed. (C) 1998 American Institute of Physi cs.