Low energy gamma ray observations of celestial objects

The MISO telescope is a double Compton gamma ray detector operating in the 0.1 - 20.0 MeV energy range, with an area of 560 cm2 and a field of view of 3.20 x 3.20 F.W.H.M. This telescope was flown on stratospheric balloons from Palestine, Texas (U.S.A.) in May 1977, October 1978 and September 1979. Results from MISO observations of the soft gamma ray emission from the Seyfert galaxies NGC 4151 (1977, 1979) and MCG 8-11-11 (1979), the BL Lac object MrK 501 (1979) and the COS B high energy (Esub(#betta#) > 100 MeV) gamma ray sources CG 135+1 (1978) and CG 195+4 (1978) are presented. Both the data on NGC 4151 and MCG 8-11-11 were found to be consistent with power laws having photon spectral indices α approximately equal to 1 in the 0.1 MeV <= Esub(#betta#) <= 3.0 MeV energy range. Above this energy, the MISO and SAS 2 measurements required spectral breaks to α > 3. The data on CG 135+1 in the 0.1 MeV <= Esub(#betta#) <= 1.0 MeV energy range were found to be compatible with a power law having a photon spectral index α approximately equal to 1, that was followed by a steepening at Esub(#betta#) >= 1 MeV. Upper limits were obtained on the emission from MrK 501 and CG 195+4. (author)