Neutral particles from Cygnus X-3 above 5×1017eV

The emission of neutral particles from Cygnus X-3 has been searched for at energies above 5×${10}^{17}$ eV, using data from the Akeno 20-${\mathrm{km}}^2$ air-shower array spanning the period December 1984 to July 1989. A 3.5σ dc excess is observed aroung the Cygnus X-3 region. This excess corresponds to a flux of (1.8±0.7)×${10}^{\mathrm{-}17}$ ${\mathrm{cm}}^{\mathrm{-}2}$ ${\mathrm{s}}^{\mathrm{-}1}$ above 5×${10}^{17}$ eV, in agreement with the Fly’s Eye data, but not the Haverah Park data. The signals do not show any 4.8-h periodicity. Their arrival times seem to be bunched in correlation with event-rate increases observed at ${10}^{16}$ eV with the Akeno 1-${\mathrm{km}}^2$ array.