Evidence for1018-eV Neutral Particles from the Direction of Cygnus X-3

Abstract

Analysis of the cumulative Fly's Eye data reveals an excess of air showers from the direction of Cygnus X-3 at energies above 0.5×${10}^{18}$ eV. No point source has previously been identified at such high energies. The probability of this excess arising as a chance clustering of isotropic cosmic rays is 6.5×${10}^{-4\mathrm{}}$. The inferred signal flux is (2.0±0.6)×${10}^{-17\mathrm{}}$ particles/${\mathrm{cm}}^2$ s. The Cygnus X-3 4.8-h periodicity is weakly present in the data.