Compton Observatory OSSE studies of supernovae and novae

A primary objective of the Compton Observatory is the direct study of explosive nucleosynthesis in supernovae and classical novae. We have been fortunate in that three rare events have coincided, relatively speaking, with the Compton Observatory launch. Supernova 1987A, roughly a once per century event, was only 4 years old at launch and so the-γ-ray flux from ⁵⁷ Co decay was not much past its peak value. Supernova 1991T, a SN Ia which exploded within a few days of launch, is a once in a decade event. It offers as good a chance as we could reasonably expect to detect the ⁵⁶ Ni and ⁵⁶ Co decays which are supposed to be responsible for the impressive SN Ia display. Nova Cygni 1992, also a once in a decade event, might be our best chance to detect-γ-rays from ²² Na, a unique nucleosynthesis byproduct of the explosive hydrogen burning thought to power classical novae. The OSSE has detected 122 keV line and Compton scattered continuum photons from ⁵⁷ Co decay in SN 1987A. The total flux of 9 × 10 ^-5 cm ^-2 s ^-1 corresponds to a ⁵⁷ Ni/ ⁵⁶ Ni production of 1.5 ± 0.5 relative to solar Fe, which is in conflict with previous interpretations of optical and infrared data. OSSE and COMPTEL upper limits on ⁵⁶ Co-γ-ray lines from SN 1991T at 3-4 ×10 ^-5 cm ^-2 s ^-1 are not in conflict with published models of SNIa at distances ≥10 Mpc. However if those models are correct, the distance must be ≤10 Mpc to give the observed optical luminosity, and are then in conflict with the-γ-ray limits. The OSSE upper limit from N Cyg 1992 near 10 ^-4 cm ^-2 s ^-1 at 1.275 MeV corresponds to an ejected ²² Na mass of 8 × 10 ^-8 M ⊙ at a distance of 1.5 kpc.