Hints of Energy Dependences in AGASA EHECR 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× 10 eV shows the small scale clustering to remain significant at the 99.5− 99.9% CL 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 degrees. The sample of events with E ≥ 6×10 eV possesses no small scale clustering. Cross correlating subsamples partitioned by energy reveals three uncorrelated distributions in the intervals 4 − 5 × 10 eV, 5− (8− 10)× 10 eV, and greater than (8− 10)× 10 eV. The partition with 5 ≤ E < 8 × 10 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. PACS number(s): 95.85.Ry, 98.70.Sa Submitted to Phys. Rev. D on 12/2/02 ∗email: burgett@utdallas.edu