Search for > 200 TeV photons from Cygnus X-3 in 1988 and 1989

Journal ArticleOver a period of 16 months from April 1988 to August 1989, we have monitored the flux of cosmic-ray showers with energies above 2X 10^14 eV. We used a two-level array of scintillators covering an area of 3 X 10^4 m2 . Counters on the surface measure the size and direction of each shower while counters buried 3 m beneath the surface sample the muons. By selecting showers with relatively few muons (less than one-tenth the average) the background of hadron-induced showers should be reduced by a factor of 150 or more while showers started by y rays should not be affected by this cut. We find no evidence for an excess from the direction of Cygnus X-3 either in ordinary showers or in muon-poor showers. For energies above 2X 10^14 eV, with 90% confidence, we find the excess flux of cosmic rays from the direction of Cygnus X-3 to be less than 1.3X 10^-13 cm-2s-1 and the flux of photons (assuming they produce muon-poor showers) to be less than 1.5X10^-14 cm-V. This limit is substantially below the level of signals reported by earlier work. The period of observation included the intense radio bursts of June and July 1989. A portion of the data covering the 77-day period surrounding these events also showed no evidence for an excess