The Production of 44Ti and 60Co in Supernovae

Abstract

The production of the radioactive isotopes ^44^Ti and ^60^Co 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 ^44^Ti 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 ^56^Ni 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 ^44^Ti in Cas A provides very interesting constraints on both the supernova environment and its mechanism. The abundances of ^44^Ti and ^60^Co ejected by Type II supernovae are such that gamma-radiation from ^44^Ti decay SN 1987A could be detected by a future generation of gamma- ray telescopes, and that the decay of ^60^Co might provide an interesting contribution to the late-time light curve of SN 1987A and other core collapse supernovae. To produce the solar ^44^Ca 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 ^56^Co 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 ^44^Ti to ^44^Ca. The Ca and Ti isotopic anomalies in presolar grains confirm the production of ^44^Ti in supernovae and that extensive mixing between zones has occurred, but a quantitative model for this mixing is presently lacking.