Searching for sources of the highest energy cosmic rays: low statistics, pitfalls, and possible clues

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The clustering properties of the highest energy cosmic rays and their correlations with candidate sources are re-examined using the most recently available AGASA data and a rigorous correlation analysis. The statistical methodology incorporates some important points not considered in previous studies. Results include small angle clustering significances consistent with, but somewhat less than, earlier findings, a possible large scale anisotropy for events with energies E ≈ 5 - 8 × 10¹⁹ eV, and no statistically significant cross correlations with BL Lacertae or blazars. A marginally significant cross correlation exists for events with energies E > 8 × 10¹⁹ eV with a set of Abell clusters, but no definitive conclusion can yet be drawn from this result.