Search for steady emission of 10-TeV gamma rays from the Crab Nebula, Cygnus X-3, and Hercules X-1 using the Tibet air shower array.

The Tibet air shower array at an altitude or 4300 m (above sea level) has been in operation since January 1990. We have searched for continual emission of 10-TeV gamma rays from the Crab Nebula, Cygnus X-3, and Hercules X-1 during the period from June 1990 through January 1992. No dc excess is found from these three sources. Flux upper limits above 10 TeV are obtained to be 1.2×10 −12 cm −2 s −1 for the Crab Nebula, 1.1×10 −12 cm −2 s −1 for Cygnus X-3, and 0.58×10 −12 cm −2 s −1 for Hercules X-1 at the 95% C.L