Linking 44Ti explosive nucleosynthesis to the dynamics of core-collapse supernovae

We have searched for the three decay lines of the 44Ti in Cassiopeia A with the spectrometer SPI on-board INTEGRAL. The lines at 78.4 and 1157.0 keV have been detected with a flux of (2.1 ± 0.7) × 10−5 ph cm−2 s−1, consistent with all previous measurements combined. The spectral capabilities of SPI indicate that the 44Ti ejecta expands at about 430 km s−1 and moves away from the observer at about 500 km s−1. Such a small expansion velocity together with the 44Ti yield of the event are consistent with a spherical explosion but an asymmetric explosion due for instance to prolate neutrino emission could not be definitely excluded.