An Observation of SN1987A with a New High Resolution Gamma-Ray Spectrometer

The discovery (Matz et al. [1]) of gamma-ray line emission at 847 and 1238 keV from radioactive 56Co in the recent supernova SN1987A proved that explosive nucleosynthesis occurred in this supernova. Gamma-ray light curves derived from these and subsequent observations (Cook et al. [2], Mahoney et al. [3], Sandie et al. [4], Rester et al. [5], Teegarden et al. [6]) have a broad plateau from August 1987 to October 1988, with an 847 keV flux of ~ 7×l0-4 ph/cm2-sec (Tueller et al. [7]). The early detection of gamma rays required the inclusion of mixing or clumping in the models, (e.g. Pinto and Woosley [8] and Chan and Lingenfelter [9]). The gamma-ray fluxes are predicted, e.g. Bussard et al. [10], to peak at about day 400 and then decrease, by a factor of ~ 6 at day 800, as the effect of increasing transparency becomes dominated by radioactive decay. Then they should depend primarily on the amount of 56Co produced and little on the degree on mixing since most of the 56Co should be exposed. Thus measurements of the 56Co gamma-ray line fluxes and profiles will continue to be important during the decline of SN1987A.