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P.A. Milne, J.D. Kurfess (Naval Research Lab), M.D. Leising (Clemson University), D.D. Dixon (University of California -Riverside), W.R. Purcell (Ball Aerospace)
The OSSE instrument on-board the CGRO is the first instrument capable of mapping the 511 keV emission that results from positron-electron annihilation. Based upon the findings of earlier, large Field of View instruments, the bulk of the mapping effort has concentrated upon the galactic center region. This effort has successfully detected emission from an extended region near the galactic center, emission from the galactic plane, and a recently reported enhancement of emission from positive latitudes (Purcell et al. 1998). Nonetheless, the OSSE instrument has observed other regions of the sky with considerable exposure, regions expected to be devoid of 511 keV emission at levels detectable by OSSE. From a study of three such regions (Virgo, South Galactic Pole, North Ecliptic Pole), as well as from a collection of AGN observations,a small scan angle dependence of the fitted 511 keV line emission was detected. We combine an expanded data set with recent (cycle 7 and cycle 8) observations, and apply the scan-angle correction, to produce maps of both the galactic center region and the Virgo region. We show these maps, and for the galactic center map, we discuss the features of this map with relation to previous maps.
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