Upper limit to the flux of neutral particles from Cygnus X-3 above 5×1017eV

We have analyzed data recorded by the Haverah Park extensive air-shower array above 5×${10}^{17}$ eV to search for a neutral particle signal from Cygnus X-3 as reported by the Fly’s Eye Group. For the period 1974 to 1987 we obtained a 95% upper limit of 4×${10}^{\mathrm{-}18}$ particles ${\mathrm{cm}}^{\mathrm{-}2}$ ${\mathrm{s}}^{\mathrm{-}1}$, in significant disagreement with the Fly’s Eye signal of (2.0±0.6)×${10}^{\mathrm{-}17}$ particles ${\mathrm{cm}}^{\mathrm{-}2}$ ${\mathrm{s}}^{\mathrm{-}1}$. The limit assumes that the neutral particles are hadronlike. For γ-ray primaries the limit is weakened to 8×${10}^{\mathrm{-}18}$ photons ${\mathrm{cm}}^{\mathrm{-}2}$ $s^{\mathrm{-}1}$ because of the reduced sensitivity of the Haverah Park array to photon primaries.