The Oriented Scintillation Spectrometer Experiment (OSSE) on the Compton Gamma-Ray Observatory has performed several observations of the Galactic plane and Galactic center region to measure the distribution of Galactic 511 keV positron annihilation radiation. Preliminary analysis of data collected during the observation of the Galactic center region over the period July 13--24, 1991, indicates the presence of a 511 keV line and positronium continuum superimposed on a power-law continuum. The line flux was found to be (2:7 \Sigma 0:5) \Theta 10 \Gamma4 fl cm \Gamma2 s \Gamma1 , with a positronium fraction of (0:9 \Sigma 0:2). The 3oe upper limit to daily variations in the 511 keV line flux from the mean during the observation interval is 3 \Theta 10 \Gamma4 fl cm \Gamma2 s \Gamma1 . If all of the observed annihilation radiation is assumed to originate from the X-ray source 1E 1740.7--2942, the corresponding 511 keV line flux would be (3:0 \Sigma 0:6) \Theta 10 \Gamma4 fl c..
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