On the cross correlation between the arrival direction of ultra-high energy cosmic rays, BL Lacertae, and EGRET detections: A new way to identify EGRET sources?

With the aim of testing recent claims for a particularly strong correlation between ultra-high energy cosmic rays (UHECRs), observed with the AGASA and the Yakutsk experiments, and a sample of BL Lacertae (BL Lacs), we here conduct a blind statistical assessment. We search for associations between the same set of BL Lac objects and the arrival directions of 33 relevant UHECRs observed with the Haverah Park and the Volcano Ranch experiments. Within the accuracy of angle determination, there are no positional coincidences. The probability that this null result arises as a statistical fluctuation from the strongly correlated case is less than 5%. This implies that the possible correlation between the arrival directions of UHECRs and BL Lacs is not statistically sustained. We discuss the impact of our findings on the propose additional connection among UHECRs, BL Lacs, and EGRET gamma-ray blazars. Recently, such an association was used as classification technique for EGRET sources. Here we show that its main underlying hypothesis, i.e., the EGRET angular uncertainty is twice that quoted in the Third EGRET Catalog, underestimates the goodness of existing gamma-ray data.