Signatures of Protons in UHECR

Original · EN

We demonstrate that the energy spectra of Ultra High Energy Cosmic Rays (UHECR) as observed by AGASA, Fly's Eye, HiRes and Yakutsk detectors, have the imprints of UHE proton interaction with the CMB radiation as the dip centered at E 1× 10¹⁹ eV, beginning of the GZK cutoff, and very good agreement with calculated spectrum shape. This conclusion about proton composition agrees with recent HiRes data on elongation rate that support the proton composition at E≥ 1× 10¹⁸ eV. The visible bump in the spectrum at E 4× 10¹⁹ eV is not caused by pile-up protons, but is an artifact of multiplying the spectrum by E³. We argue that these data, combined with small-angle clustering and correlation with AGN (BL Lacs), point to the AGN model of UHECR origin at energies E ≤ 1× 10²⁰ eV. The events at higher energies and the excess of the events at E ≥ 1× 10²⁰ eV, which is observed by AGASA (but absent in the HiRes data) must be explained by another component of UHECR, e.g. by UHECR from superheavy dark matter.