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

Abstract

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.