Hints of energy dependences in AGASA extremely high energy cosmic ray arrival directions

A correlation and probability analysis of the distribution of arrival directions for a sample of AGASA events reported to have energies above $4\times {10}^{19}\mathrm{eV}$ shows the small scale clustering to remain significant at the 99.5–99.9% C.L. and to be consistent with previous results. For the sample taken as a whole, there are no departures from either homogeneity or isotropy on angular scales greater than $5°.$ The sample of events with $E>~6\times {10}^{19}\mathrm{eV}$ contains no pairs with separations $<4\mathrm{}°.$ Cross correlating subsamples partitioned by energy reveal three uncorrelated distributions in the intervals $(4\mathrm{}–5)\times {10}^{19}\mathrm{eV},$ $(5\mathrm{}–8)\times {10}^{19}\mathrm{eV},$ and greater than $8\times {10}^{19}\mathrm{eV}.$ The partition with $5<~E<\mathrm{}8\mathrm{}\times {10}^{19}\mathrm{eV}$ is correlated with the supergalactic equatorial plane while the other two groups are statistically consistent with isotropic distributions. The presence of three distinct energy-partitioned groups of events could reflect possible changes in primary composition, different source distributions, differing levels of GZK losses, or deflection effects of magnetic fields.