Ultra high-energy gamma-ray observations of Geminga

Results of the observations of Geminga (2CG 195 + 4) in the energy range above 10 trillion eV, carried out in 1979, 1981, and 1983 with the Tien Shan high-altitude facility for recording the Cerenkov flashes of extensive air showers are reported. The mean flux density averaged over the whole protracted data is (5.7 + or - 25) x 10 to the -11th quanta/cm per s. The flux is variable with a period of about 59 s. The character of the period variation with time is hard to be reconciled with earlier findings by other authors. The importance of further simultaneous observations at various energies is indicated. (Author)