The Pierre Auger Collaboration

The Pierre Auger Collaboration has reported evidence for anisotropies in the arrival directions of cosmic rays with energies larger thanEth = 55 EeV. There is a correlation above the isotropic expectation with nearby active galaxies and the largest excess is in a celestial region around the position of the radio galaxy Cen A. If these anisotropies are due to nuclei of charge Z, the protons accelerated in those sources are expected, under reasonable assumptions, to lead to excesses in the same regions of the sky at energies above Eth/Z. We here report the lack of anisotropies at these lower energies for illustrative values of Z = 6, 13 and 26. These observations set stringent constraints on the allowed proton fraction at the sources.