THE CO-57 ABUNDANCE IN SN-1987A

We discuss several astrophysical consequences of the detection by OSSE (Kurfess et al. 1992) of Co-57 gamma radiation from supernova 1987A. Models with low photoelectric absorption cannot account for both OSSE data and the bolometric luminosity. By burying the alpha-rich-freezeout portion at deeper gamma depths than in published models, we show that it remains barely possible that the bolometric luminosity during days 1200-1800 could derive from Co-57 power without requiring 57/56 production ratios greater than twice solar. We illustrate this by slowing the expansion within the inner four solar masses of ejecta in model 10HMM. A successful fit to both total radiated power and to OSSE Co-57 flux can be attained. However, that "slow core" model may then be too opaque near day 500-700 to allow for the suggested decline of the bolometric light curve below exponential during that earlier period. We also propose alternative mechanisms which may contribute to the bolometric power at late times: (1) stored power owing to delayed emission of thermalized gamma-ray energy. Mechanisms include (a) delayed release of chemical power owing to decreasing ionization, for which we present a simple analytic theory; or, (b) increasing time delay for suprathermal electrons to strike dust grains; (2) dissipation at rate 10(-13) s-1 of mechanical energy owing to collisions within the ejecta. Because of the importance of Fe isotopic ratios to chemical evolution of the Galaxy, we outline the resulting chemical evolution problem for the solar Fe-57 abundance.