Implications of a Possible Clustering of Highest Energy Cosmic Rays

Very recently, a possible clustering of a subset of observed ultrahigh energy cosmic rays above about 40EeV (4x10^19eV) in pairs near the supergalactic plane was reported. We show that a confirmation of this effect would provide information on origin and nature of these events and, in case of charged primaries, imply interesting constraints on the extragalactic magnetic field. The observed time correlation would most likely rule out an association of these events with cosmological gamma ray bursts. If no prominent astrophysical source candidates such as powerful radiogalaxies can be found, the existence of a mechanism involving new fundamental physics would be favored.