2004/04/24 by Hiroyuki Yoshiguchi, Shigehiro Nagataki, Katsuhiko Sato
Physics and Astronomy · #Astrophysics and Cosmic Phenomena #Dark Matter and Cosmic Phenomena #Gamma-ray bursts and supernovae #astro-ph
paper · pdf · doi:10.1086/423486
published as Astrophys.J. 614 (2004) 43-50 · 8 pages, 7 figures
arxiv created 2004/04/24 · openalex publication_date 2004/10/08 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/07/31
Recently, the High Resolution Fly's Eye (HiRes) experiment has indicated that there is no small-scale anisotropy in the arrival distribution of ultra-high-energy cosmic rays (UHECRs) above E > 10 19 eV, contrary to the Akeno Giant Air Shower Array (AGASA) observation. In this paper we discuss the statistical significance of this discrepancy between the two experiments. We calculate the arrival distribution of UHECRs above the 10 19 eV predicted by the source models constructed using the Optical Redshift Survey galaxy sample. We apply a new method developed by us for calculating arrival distribution in the presence of the Galactic magnetic field. The great advantage of this method is that it enables us to calculate the UHECR arrival distribution with lower energy (~10 19 eV) than previous studies within a reasonable time by following only the trajectories of UHECRs actually reaching the Earth. It has been realized that the small-scale anisotropy observed by the AGASA can be explained with the source number density ~10 -6 to 10 -5 Mpc -3 , assuming a weak extragalactic magnetic field ( B ≤ 1 nG). We find that the predicted small-scale anisotropy for this source number density is also consistent with the current HiRes data. We thus conclude that the statement by the HiRes collaboration that they do not find small-scale anisotropy in the UHECR arrival distribution is not statistically significant at present. We also examine the future prospect of determining the source number density with an increasing amount of observed data.