Search for Cross-Correlations of Ultra--High-Energy Cosmic Rays

The High Resolution Fly's Eye (HiRes) experiment is a stereo air fluorescence detector for the study of cosmic rays with energies above $5\times 10^{17}$\,eV. Arrival directions of cosmic rays observed in stereo can be resolved with a typical uncertainty on the order of $0.5^{\circ}$, making the experiment ideal for small-scale anisotropy studies. We will review recent claims of evidence for correlations between ultrahigh-energy cosmic rays and active galaxies of the BL Lac subclass, and we will describe tests of these claims with new data.