1996A&AS..120C...5K

Key results obtained by the OSSE instrument during the first four years of the Compton Gamma Ray Observatory mission are presented. OSSE has undertaken extended observations of the gamma ray emission from the galactic center region and found the positron annihilation radiation to be consistent with a two-component model: a spheroidal component located at the galactic center and a weaker galactic disk component. Simultaneous observations with the SIGMA imaging instrument have provided the first low-energy gamma ray spectrum of the diffuse continuum emission from the galactic center region.
Result. on galactic sources include the spectral observations of two new rotation-powered pulsars, PSR 1509-58 and Vela, the discovery of 110keV cyclotron emission from the Be X-ray binary A0535+26, and the discovery that galactic black hole transients have two spectral classes: thermal and power-law. Extragalactic sources also have two spectral classes. Seyfert galaxies are typified by thermal spectral with exponential cutoffs from 50 to several hundred keV, while blazars exhibit power-law spectra that extend into the EGRET energy range. Blazar spectra also often have a spectral break in the MeV region. OSSE has also obtained several observations of supernovae, including the first detection of ⁵⁷Co from SN 1987A, hard X-ray emission from a shock-heated pre-SN wind in SN 1993J, and upper limits for ⁴⁴Ti and ⁵⁶Co emission from Cas A and SN 1991T resp. Finally, recent observations to confirm the COMPTEL observation of 4.4 and 6.1MeV line emission from the Orion region have provided only upper limits, thereby placing constraints on the intensity and/or distribution of the emission.