Search for signals from Cygnus X-3 at energies above 50 TeV

Upper limits for the time-averaged flux of air showers from the direction of Cygnus X-3 during the calendar period 2 April 1986 to 3 May 1987 are found to be 1.5×${10}^{\mathrm{-}13}$ ${\mathrm{cm}}^{\mathrm{-}2}$ ${\sec }^{\mathrm{-}1}$ for all events, and 7.6×${10}^{\mathrm{-}14}$ ${\mathrm{cm}}^{\mathrm{-}2}$ ${\sec }^{\mathrm{-}1}$ for events with no observed muons in a 44-${\mathrm{m}}^2$ muon detector. These are integral fluxes above 50 TeV on the assumption of an $E^{\mathrm{-}1}$ primary spectrum. A possible observation of a short-term signal from Cygnus X-3, with an anomalous muon content, phase correlated with the 4.8-h orbital period, with an integral flux above 50 TeV of (8.2±2.0)×${10}^{\mathrm{-}13}$ ${\mathrm{cm}}^{\mathrm{-}2}$ ${\sec }^{\mathrm{-}1}$ is also reported.