GRIS Observations of Supernova 1987A: The Gamma-Ray Continuum

Observations from two flights of a balloon-borne germanium gamma ray spectrometer system will be presented. The Gamma Ray Imaging Spectrometer (GRIS) consists of an array of 7 very large n-type detectors with an effective area of 198.5 cm sup 2 at 100 keV. The array is housed in a very heavy active NaI shield (>15 cm pathlength) for background rejection and collimation (20degrees fwhm field of view). The supernova was observed during a 24 hour flight launched in Alice Springs, Australia on 30 April 1988 at 19:58 UT. The instrument is presently being prepared for another flight in late October or early November of 1988 from Alice Springs. A continuum spectrum for energies >50 keV will be presented from the April flight and we hope to present results >20 keV for the fall flight. The continuum we observed will be interpreted as resulting from compton scattering of the gamma ray lines from the decay of sup (56) Co producted in the supernova explosion. Our direct observations of the lines are presented in another talk at this meeting.