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The Tibet air-shower array operating at Yangbajing (4300 m above sea level) is sensitive to gamma-ray air showers at energies as low as 3 TeV. The observation of the moon’s shadow has provided a direct check of the angular resolution, the energy estimation and the systematic pointing error of this air-shower array. Using these data, we have searched for multi-TeV gamma-ray emission from 21 SNRs located within 5 kpc distance in the declination band of 0° to +60°. The signal from the Crab Nebula was detected at 5.5 σ level as described another paper. No significant DC excess exceeding 5 σ level was found from any of these SNRs except from the Crab Nebula. The results of nearby eight SNRs piled up gave a flux upper limit slightly lower than the expected values for a simple model of shock acceleration.

Tibet II Air Shower Array consisting of scintillation counters with lattice of 15 m spacing has been operated with very high trigger rate of about 200 Hz. The threshold enegy of this array is estimated to be about 8 TeV for proton induced showers. Tibet High Density (HD) Array with 7.5 m spacing has been operated with the trigger rate of 115 Hz. The Mode energy of this array is estimated to be about 3 TeV for proton showers. Angular resolution of the arrays are estimated to be 0.9 degree above 10 TeV for Tibet II array, and 0.85 degree above TeV for HD array, resepectively. The angular resolution of these arrays and other array performances are examined by observing the Moon shadow resulting from the cosmic ray deficit in the direction of the Moon. Using the deflection of the Moon shadow to the east-west direction, the error of the array can be estimated by observing the displacement of the shadow in the north-south direction, because it is free from the effect of geomagnetic field, especially at Yangbajing in Tibet. The calibrations such as primary energy, angular resolution and pointing errors, directly using the Moon shadow has first been done by the Tibet experiment.

The Tibet air-shower array operating at Yangbajing (4300 m above sea level) is sensitive to gamma-ray air showers at energies as low as 3 TeV. The observation of the Moon’s shadow has provided a direct check of the angular resolution, the energy estimation and the systematic pointing error of this air-shower array. Using these data, we have searched for multi-TeV gamma-ray emission from 27 SNRs located within 10 kpc distance in the declination band of −10° to +70°. The signal from the Crab Nebula was detected at 5.5 σ level. The intensity observed is (4.61±0.90)×10−12 cm−2 s−1 TeV−1 at 3 TeV. No significant DC excess was found from any of these SNRs except from the Crab Nebula.

The Tibet ASγ experiment, which has started since January, 1990, is located at an altitude of 4,300m at Yangbaging in Tibet, China (90.5° E, 301° N). The air‐shower array is composed of 49 scintillation counters for fast timing (FT), each counter having an area of 0.5 m2, in a grid pattern with a spacing of 15 m and 16 density detectors. The density detectors surrounding the FT detectors are planned to select the showers of which core are inside the FT array. For the constant and continuous opeation, the system for laser calibration, the ADC,TDC module calibration and the power check system were installed. A Rb clock is used for the phase analysis of γ‐rays.The array is usually operated by the trigger rate of ∼20Hz with any 4‐fold coincidence of the FT detectors. The analysis of experimental data shows that the performance of array is realized as expected by the Monte Carlo simulation. For the events of which core are inside the FT array, are obtained the following results. The detection threshold energy for γ‐rays is ∼40 TeV; the peak energy 20 TeV. The angular resolution around 100 TeV is ∼0.5°. The systematic error of arrival direction is considerably smaller than the angular resolution in the concerned energy region.