Correlation function of ultra-high energy cosmic rays favors point sources

We calculate the angular two-point correlation function of ultra-high energy cosmic rays (UHECR) observed by AGASA and Yakutsk experiments. In both data sets, there is a strong signal at highest energies, which is concentrated in the first bin of the size of the angular resolution of the experiment. For the uniform distribution of sources, the probability of a chance clustering is $4\cdot10^{-6}$. Correlations are absent or not significant at larger angles. This favors the models with compact sources of UHECR.