Numerical study of propagation of UHECRs: Spectrum, arrival direction, composition

In this paper, simulations of propagation of UHE-protons from nearby galaxies are presented. We found good parameter sets to explain the arrival distribution of UHECRs reported by AGASA and the energy spectrum reported by HiRes. Using a good parameter set, we demonstrated what distribution of arrival direction of UHECRs will be as a function of event numbers. We show that 1000-10000 events are necessary to clearly see the source distribution. We also showed that effects of interactions and trapping of UHE-Nuclei in a galaxy cluster are very important. Especially, when a UHECR source is a bursting source such as a GRB/AGN flare, heavy UHE-Nuclei are trapped for a long time in the galaxy cluster, which changes the spectrum and chemical composition of UHECRs coming from the galaxy cluster. We also showed that such effects can be important when there have been sources of UHE-Nuclei in the Milky Way. Since light nuclei escape from the Milky Way in a short timescale, the chemical composition of UHECRs observed at the Earth can be heavy at the high-energy range as suggested by Auger.