Part i - Ultra High Energy Gamma Rays from Cygnus X-3. Part II - Properties of the Galactic Gamma Ray Source Population.

The detection of gamma rays with energies greater than 500 GeV from the variable X-ray source Cygnus X-3 is reported. The gamma ray emission is modulated at the same 4.8 hour period as the X-ray emission and the peak in the gamma ray light curve is in phase with the X-ray maximum. The gamma ray signal above 500 GeV is found to be 10.9 (+OR-) 2.5% of the cosmic ray background, corresponding to a flux of 8 x 10('-11) photons/cm('2)-sec averaged over the cycle. The galactocentric distribution of gamma ray emissivity is derived from the galactic longitude flux profile of 70 MeV to 5 GeV gamma rays as seen by the COS-B satellite. With the assumption that the gamma ray sources are distributed like the total emmissivity, it is found that 30% of the total emission is contributed by the discrete sources. This result is independent of the luminosity function of the source population.