COMPTEL observations of 44Ti gamma-ray line emission form 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/(cm^2^.s). During two observation periods in July 1992 and February 1993 the Galactic plane in the region of the young supernova remnant Cas A was observed, showing evidence for line emission at 1.16 MeV from the decay of ^44^Ti at a significance level of ~4 sigma. This is the first time a supernova remnant has been detected in the gamma-ray line from ^44^Ti decay. Adopting a distance of 2.8 kpc to the Cas A remnant, the measured line flux (7.0+/-1.7).10^-5^ photons/(cm^2^.s), can be translated into a ^44^Ti mass ejected during the Cas A supernova explosion, between (1.4+/-0.4).10^-4^ M_sun_ and (3.2+/-0.8).10^-4^ M_sun_, depending on the precise value of the ^44^Ti mean life time and on the precise date of the event. Implications of this result for supernova nucleosynthesis models are discussed.