Propagation and Signatures of Ultra High Energy Cosmic Rays

Abstract

We study the extragalactic protons with universal spectrum, which is independent of mode of propagation, when distance between sources is less than the propagation lengths, such as energy attenuation length or diffusion length (for propagation in magnetic fields). The propagation features in this spectrum, the GZK cutoff, dip and bump, are studied with help of modification factor, which weakly depends on the generation spectrum index $\gamma_g$. We argue that from the above features the dip is the most model-independent one. For the power-law generation spectrum with $\gamma_g=2.7$ the dip is very well confirmed by the data of all existing detectors, which gives the strong evidence for extragalactic protons propagating through CMB. We develop the AGN model for origin of UHECR, which successfully explains the observed spectra up to $1\times 10^{20}$ eV and transition from galactic to extragalactic cosmic rays. The calculated spectrum has the GZK cutoff, and the AGASA excess of events at $E \gsim 1\times 10^{20}$ eV needs another component, e.g. from superheavy dark matter. In case of weak extragalactic magnetic fields this model is consistent with small-angle clustering and observed correlation with BL Lacs.