Maximum Likelihood Method for Cross Correlations with Astrophysical Sources

TL;DR

This paper introduces a generalized maximum likelihood method to analyze cross correlations between astrophysical sources and sparse cosmic ray data, improving detection capabilities for sources like gamma rays and neutrinos.

Contribution

The authors develop a new maximum likelihood approach that accounts for varying source luminosities, enhancing correlation analysis in sparse astrophysical datasets.

Findings

Detected a significant correlation between HiRes UHECRs and BLLacs

The method shows improved sensitivity over previous techniques

Chance probability of observed correlation is 6×10^-5

Abstract

We generalize the Maximum Likelihood-type method used to study cross correlations between a catalog of candidate astrophysical sources and Ultrahigh Energy Cosmic Rays (UHECRs), to allow for differing source luminosities. The new method is applicable to any sparse data set such as UHE gamma rays or astrophysical neutrinos. Performance of the original and generalized techniques is evaluated in simulations of various scenarios. Applying the new technique to data, we find an excess correlation of about 9 events between HiRes UHECRs and known BLLacs, with a 6*10^-5 probability of such a correlation arising by chance.