A. C. Rester, G. Eichhorn, and R. L. Coldwell, University of Florida; J. I. Trombka, Goddard Space Flight Center; R. Starr, Catholic University of America; and G. P. Lasche, DARPA/NMO, telex: "The Gamma-Ray Advanced Detector (GRAD) Antarctic Supernova Observer was successfully launched from Williams Field near McMurdo Station, Antarctica, on Jan. 8.01 UT. The balloon achieved a float altitude of 36 km and drifted westward along -78 deg latitude with a speed of about 7 m/s. After 3 days at float altitude, there were power supply failures, so the flight was terminated and the payload recovered 360 km west of Vostok. We achieved about 12 hr of observation in the direction of SN 1987A (detecting both continuous and discrete line gamma-ray spectral features) and about 9 hr in a direction away from the supernova. Preliminary analysis of the 847-keV and 1238-keV regions shows broad line structure with possible line splitting. The shape in the 847-keV region is somewhat obscured by the 844-keV Al background line. The structure in the 1238-keV region extends from about 1216 keV to about 1244 keV; if this feature is associated with the 56Co decay in the supernova, our results would indicate an expansion velocity of about 1300 +/- 300 km/s and a recessional velocity significantly > 270 km/s. Tentative estimates of the fluxes in these two regions are both about 0.0025 +/- 0.0013 photons/cm2/s. Verification of these preliminary results awaits more detailed analysis." Visual magnitude estimates by A. C. Beresford, Adelaide, South Australia: Jan. 20.54 UT, 6.3; 21.48, 6.4; 22.48, 6.3.
International Astronomical Union Circular
- Pub Date:
- January 1988