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Session 93 - GRIS.
Oral session, Wednesday, January 15
Piers 2/3,

[93.03] GRIS Detections of Positron Annihilation Radiation from Our Galaxy

L. Cheng, M. Leventhal (UMD), J. Tueller, N. Gehrels, A. Parsons, B. J. Teegarden (NASA/GSFC), S. D. Barthelmy, J. E. Naya (USRA/GSFC), L. M. Bartlett (NASNRC/GSFC)

The Gamma-Ray Imaging Spectrometer (GRIS) was flown by balloon over Alice Springs, Australia on 1995 Oct. 4 and 24. The Galactic center passed through the field of view of one and a half times and the Galactic plane at l=240 passed the field of view once. The electron/positron annihilation line was detected in both the Galactic center transits and the line flux and width was found to be 1.1\pm0.1\times10^-3 photons cm^-2 s^-1 and 2.9\pm0.5 keV, respectively. An excess of 511 keV line flux was observed during the Galactic plane transit and this might be due to unknown 511 keV source. The line flux and line width of this unknown source is 5.3\pm1.3\times10^-3 photons cm^-2 s^-1 and 3.0\pm0.7 keV. The flux observed by GRIS was in good agreement with the TGRS instrument on WIND but is only about 1/2 the flux observed in the SMM wide field drift scans. We will discuss the significance of these apparent differences.

Program listing for Wednesday