GZK Photons as Ultra High Energy Cosmic Rays
Abstract
We calculate the flux of "GZK-photons", namely the flux of Ultra High Energy Cosmic Rays (UHECR) consisting of photons produced by extragalactic nucleons through the resonant photoproduction of pions, the so called GZK effect. We We calculate the flux of "GZK-photons", namely the flux of Ultra High Energy Cosmic Rays (UHECR) consisting of photons produced by extragalactic nucleons through the resonant photoproduction of pions, the so called GZK effect. We show that, for primary nucleons, the GZK photon fraction of the total UHECR flux is between and above eV and up to the order of 0.1 above eV. The GZK photon flux depends on the assumed UHECR spectrum, slope of the nucleon flux at the source, distribution of sources and intervening backgrounds. Detection of this photon flux would open the way for UHECR gamma-ray astronomy. Detection of a larger photon flux would imply the emission of photons at the source or new physics. We compare the photon fractions expected for GZK photons and the minimal predicted by Top-Down models. We find that the photon fraction above eV is a crucial test for Top-Down models.
Cite
@article{arxiv.astro-ph/0506128,
title = {GZK Photons as Ultra High Energy Cosmic Rays},
author = {Graciela B. Gelmini and Oleg E. Kalashev and Dmitry V. Semikoz},
journal= {arXiv preprint arXiv:astro-ph/0506128},
year = {2008}
}
Comments
21 pages, 18 figures with 35 panels in version 3 (substantial changes to the "Topological defects", "SHDM" and "Photon fractions" subsections were made with respect to version 2)