Galactic gamma-ray emission from discrete and diffuse sources

The scientific potential of gamma-ray astronomy has long been recognised because of its direct relationship to astrophysical processes involving high energy electrons and protons and because the high penetrating power of gamma rays enables them to reach the Earth from many parts of the Galaxy or universe.The first unambiguous detection of celestial gamma rays was made by Kraushaar et al (1972), who observed gamma rays from the Galactic disc with a peak intensity towards the Galactic centre.In order to measure the spectrum of the Galactic gamma emission, a series of balloon flights was carried out by the Imperial College group.The flights took place over Australia using instruments designed to detect gamma photons in the energy range 0.2<E<5.0GeV.Results from the 1973 flight and the two 1975 flights are presented here.The results from the Galactic plane are consistent with the emission spectrum as reported by COS-B.Upper limits on the emission of various possible sources of gamma rays are quoted.In the final chapter, the possible pulsar contribution to the Galactic gamma-ray emission is examined.This study was prompted following the detection of pulsed gamma radiation from the Crab and Vela radio pulsars.Using the latest pulsar data from the Molonglo Radio Observatory, Australia, the contribution is estimated to be £l0%.Density values on the equatorial plane as a function of galactocentric radius.