Detection of the 67.9 Kev and 78.4 Kev Lines Associated with the Radio-active Decay of Ti in Cassiopeia A

We report the detection of the Sc nuclear decay lines at 67.9 keV and 78.4 keV associated with the nuclear decay of Ti in Cassiopeia A. The line emission was observed by the PDS instrument on board BeppoSAX, which recently observed the supernova remnant for over 500 ks. The detection of the line emission with a flux of (2.1± 0.7) 10 ph/cm/s in each line (90% confidence) is at the 5σ significance level, if we can assume that the 12-300 keV continuum is adequately represented by a single power law. However, as the nature of the continuum is not clear we investigate various other possibilities. A more conservative estimate of the line flux is made by assuming that a power law continuum is at least a good approximation to the continuum emission for a narrower 30-100 keV energy range. With this limitation the measured line flux is (1.9 ± 0.9) 10 ph/cm/s, with the detection still at the 3.4σ significance level. We suggest that together with the CGRO-COMPTEL measurement of the Ca line at 1157 keV of (3.3 ± 0.6) 10 ph/cm/s a flux for all three lines of (2.5 ± 1.0) 10 ph/cm/s for Cas A can be adopted. This implies an initial Ti mass of (0.8− 2.5) 10 M⊙. Subject headings: gamma rays: observations – ISM: individual (Cassiopeia A) – nuclear reactions, nucleosynthesis, abundances – supernova remnants – X-rays: ISM