Clustering properties of ultrahigh energy cosmic rays and the search for their astrophysical sources

Abstract

The arrival directions of ultrahigh energy cosmic rays (UHECRs) may show anisotropies on all scales, from just above the experimental angular resolution up to medium scales and dipole anisotropies. We find that a global comparison of the two-point auto-correlation function of the data with the one of catalogues of potential sources is a powerful diagnostic tool. In particular, this method is far less sensitive to unknown deflections in magnetic fields than cross-correlation studies while keeping a strong discrimination power among source candidates. We illustrate these advantages by considering ordinary galaxies, gamma ray bursts and active galactic nuclei as possible sources. Already the sparse publicly available data suggest that the sources of UHECRs may be a strongly clustered sub-sample of galaxies or of active galactic nuclei. We present forecasts for various cases of source distributions which can be checked soon by the Pierre Auger Observatory.

11 pages, 8 figures, 4 tables; minor changes, matches published version

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• Lecture notes on high energy cosmic rays
• A global autocorrelation study after the first Auger data: impact on the number density of UHECR sources
• The GZK horizon and constraints on the cosmic ray source spectrum from observations in the GZK regime
• Correlations between Ultrahigh Energy Cosmic Rays and Infrared-Luminous Galaxies
• Astrophysical interpretation of the medium scale clustering in the ultra-high energy sky
• Multiscale autocorrelation function: a new approach to anisotropy studies
• A Three-Point Cosmic Ray Anisotropy Method
• Dark Matter implications of the Fermi-LAT measurement of anisotropies in the diffuse gamma-ray background: status report
• Anisotropy studies with multiscale autocorrelation function