Estimate from Gulmarg of PeV photon flux from Cygnus X-3 and its relevance

Atmospheric pulses recorded at Gulmarg, India between January 1976 and December 1977 using wide-angle photomultipliers indicate a phase-dependent component exhibiting the Cygnus X-3 modulation period of 4.8 hr, and an amplitude, determined by the number of excess events in the phase peak relative to the total phase-independent events, of 1.8 + or - 0.4 percent (corresponding to a detected average flux of 1.6 + or - 0.4 gamma/sq cm per s above 0.5 PeV). The possibility of a long-term reduction in the luminosity of the PeV source by a factor of about 1.5/yr is also suggested by Haverah Park phase histograms of Cygnus X-3 obtained between January 1979 and December 1984, and by Plateau Rosa data from the December 1981 to March 1985 period. After accounting for losses in the PeV photon beam due to gamma-gamma interactions with the 2.7 K microwave background, the ultrahigh energy photon fluxes in the 10 to the 11th to 10 to the 12th eV region are found to be much lower than those of Cygnus X-3. 65 references.