The Oriented Scintillation Spectrometer Experiment (OSSE) on the Compton Gamma Ray Observatory has observed SN 1987A for two 2 week periods during the first 9 months of the mission. Evidence for gamma-ray line and continuum emission from 57Co is observed with an intensity of about 10-4 gamma cm-2 s-1. This photon flux between 50 and 136 keV is demonstrated by Monte Carlo calculations to be independent of the radial distribution of 57Co for models of low optical depth, viz., models having photoelectric absorption losses of 122 keV photons no greater than several percent. For such models the observed 57Co flux indicates that the ratio 57Ni/56Ni produced in the explosion was about 1.5 times the solar system ratio of 57Fe/56Fe. When compared with nearly contemporaneous bolometric estimates of the luminosity for SN 1987A, our observations imply that 57Co radioactivity does not account for most of the current luminosity of the supernova remnant in low optical depth models. We suggest alternatives, including a large optical depth model that is able to provide the SN 1987A luminosity and is consistent with the OSSE flux. It requires a 57/56 production ratio about twice solar.
- Gamma rays: observations
- Nuclear reactions, nucleosynthesis, abundances
- Supernovae: individual (SN 1987A)
- X-rays: general
ASJC Scopus subject areas
- Astronomy and Astrophysics
- Space and Planetary Science