The Production of Ti44 and Co60 in Supernova
Abstract
The production of the radioactive isotopes 44Ti and 60Co in all types of supernovae is examined and compared to observational constraints including Galactic γ--ray surveys, measurements of the diffuse 511 keV radiation, γ--ray observations of Cas A, the late time light curve of SN 1987A, and isotopic anomalies found in silicon carbide grains in meteorites. The (revised) line flux from 44Ti decay in the Cas A supernova remnant reported by COMPTEL on the Compton Gamma-Ray Observatory is near the upper bound expected from our models. The necessary concurrent ejection of 56Ni would also imply that Cas A was a brighter supernova than previously thought unless extinction in the intervening matter was very large. Thus, if confirmed, the reported amount of 44Ti in Cas A provides very interesting constraints on both the supernova environment and its mechanism. The abundances of 44Ti and 60Co ejected by Type II supernovae are such that gamma-radiation from 44Ti decay SN 1987A could be detected by a future generation of gamma-ray telescopes and that the decay of 60Co might provide an interesting contribution to the late time light curve of SN 1987A and other Type II supernovae. To produce the solar 44Ca abundance and satisfy all the observational constraints, nature may prefer at least the occasional explosion of sub-Chandrasekhar mass white dwarfs as Type Ia supernovae. Depending on the escape fraction of positrons due to 56Co made in all kinds of Type Ia supernovae, a significant fraction of the steady state diffuse 511 keV emission may arise from the annihilation of positrons produced during the decay of 44Ti to 44Ca. The Ca and Ti isotopic anomalies in pre-solar grains confirm the production of 44Ti in supernovae and that
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