The Production of Ti44 and Co60 in Supernova

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 ${\hat{I}}^3$--ray surveys, measurements of the diffuse 511 keV radiation, ${\hat{I}}^3$--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 Type II 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 pre-solar grains confirm the production of ${}^{44}$Ti in supernovae and that

27 pages including 7 figures. uuencoded, compressed, postscript. in press ApJ