Indications of a Cosmic Ray Source in the Perseus-Pisces Supercluster*

The Telescope Array experiment is the largest observatory studying ultrahigh energy cosmic rays in the northern hemisphere. In this talk, we report a newly found excess of events on the sky with energies, E ≥ 10^19.4 eV. The local significance of the excess is calculated to be about 4 standard deviations by using the Li-Ma oversampling method with a 20°-radius circle. The excess appears in the region of the Perseus-Pisces supercluster (PPSC). This is the closest supercluster within the TA’s field of view other than the local supercluster of which we are a part. In addition, the major portion of the foreground between the Earth and the PPSC as well as the space beyond the PPSC in the same direction, are nearly empty. This motivates us to conduct a Monte-Carlo study to estimate the probability that an excess of events can occur close to the PPSC by chance. The chance probability of having an excess close to the PPSC is estimated to be 3.5 standard deviations. The result indicates a cosmic ray source likely exists in the PPSC.