COMPTEL observations of 44Ti gamma-ray line emission from Cas A

The COMPTEL telescope on board the Compton Gamma‐Ray Observatory (CGRO) is capable of imaging gamma‐ray line sources in the MeV region at a sensitivity of the order of 10−5 photons/(cm2s). 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. Imaging and spectral analyses show evidence for line emission of 44Ti at 1.16 MeV from a position of Cas A at a significance level of ∼4 σ.This is the first time a supernova remnant has been detected in the gamma‐ray line from 44Ti decay. If the Cas A supernova remnant is placed at 2.8 kpc then the measured line flux can be translated into a 44Ti mass, ejected during the Cas A supernova explosion, between (1.40±0.35) ⋅ 10−4 M⊙ and (3.2±0.8) ⋅ 10−4 M⊙, depending on the precise value of the 44Ti mean life time value and on the precise date of the event. Implications of this result for supernova nucleosynthesis models are discussed.