Gamma-ray observations of supernova SN1987A by the balloonborne gamma-ray advanced detector

On 8 January 1988, gamma-ray advanced detector (GRAD) supernova observer was launched on a 3.3 x 105 cubic meter helium balloon from Williams Field. The instrument maintained a float altitude of 36 kilometers as it drifted eastward along the 78 degrees S parallel until it was brought down 320 kilometers east of Vostak Station on 10 January and recovered on 13 January. High-energy resolution gamma-ray spectra of the supernova SN1987A were taken; it is hoped that these spectra will provide evidence of explosive nucleosynthesis of the heavy elements in the supernova. Results. The earliest results of the analysis, showed evidence of gamma rays from the radioactive decay of the isotope cobalt-56, the longer-lived daughter of short-lived nickel-56, which was expected to be produced in great abundance in the supernova explosion, but the cobalt-56 line appearing most clearly in the supernova spectrum-the 1,238-kiloelectronvolt gamma-ray--was apparently split into two doppler-shifted and broadened components. This astonishing result appeared to suggest that the mantle of the supernova had expanded asymmetrically with a velocity in excess of 3,000 kilometers per second