COMPTEL OBSERVATIONS OF TI-44 GAMMA-RAY LINE EMISSION FROM CAS-A

The COMPTEL telescope aboard the Compton Gamma-Ray Observatory (CGRO) is capable of imaging gamma-ray line sources in the MeV region with a sensitivity of the order 10(-5) photons/(cm2s). During two observation periods in July 1992 and February 1993 the Galactic plane in the regi on of the young supernova remnant Cas A was observed, showing evidence for line emission at 1.16 MeV from the decay of Ti-44 at a significan ce level of approximately 4 sigma. This is the first time a supernova remnant has been detected in the gamma-ray line from Ti-44 decay. Adop ting a distance of 2.8 kpc to the Cas A remnant, the measured line flu x (7.0 +/- 1.7).10(-5) photons/(cm2 s), can be translated into a Ti-44 mass ejected during the Cas A supernova explosion, between (1.4 +/- 0 .4).10(-4) M. and (3.2 +/- 0.8).10(-4) M., depending on the precise va lue of the Ti-44 mean life time and on the precise date of the event. Implications of this result for supernova nucleosynthesis models are d iscussed.