Massive galaxy clusters and the origin of Ultra High Energy Cosmic Rays

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We investigate whether ultra--high energy cosmic rays (UHECR) may be preferentially produced in massive galaxy clusters, by looking for correlations between UHECR directions and those of x-ray clusters. We find an excess-above-random of high energy cosmic rays which correlate with massive galaxy cluster positions. For cosmic rays with energies above 50 EeV the observed correlation is the strongest or angles of 1.2-1.6 degrees where it has a chance probability of about 0.1%. Including lower energy cosmic rays in the sample causes the angle where the most significant correlation is found to increase, as would be expected by virtue of instrumental and magnetic smearing increasing at lower energy. These results suggest that some UHECR are produced in galaxy clusters, or in objects that preferentially populate galaxy clusters.