  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.
