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 +- 2.5% of the cosmic ray background, corresponding to a flux of 8 x 10-11 photons/cm2-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