The Oriented Scintillation Spectrometer Experiment (OSSE) observations of the Galactic plane and Galactic center region have been combined with scanning observations by the Transient Gamma-Ray Spectrometer (TGRS) and Solar Maximum Mission (SMM) instruments to produce maps of the Galactic narrow 511 keV positron annihilation line radiation. Two di †erent mapping methods, singular value decomposition and maximum entropy, have been applied to the data. In both cases, the resulting maps show evidence for three distinct features : (1) a central bulge, (2) emission in the Galactic plane, and (3) an enhancement or extension of emission at positive latitudes above the Galactic center. Modeling of the data conÐrmed the existence of these features. The derived distribution is found to be in good qualitative agreement with nearly all of the historical observations of narrow 511 keV line emission from the Galactic center region. No evidence of time variability is found. Various possible production mechanisms for the observed positrons, including the positive-latitude enhancement, are presented. It is found that supernovae are capable of producing positrons at the required rate to account for the intensity and morphology of the observed 511 keV line emission.

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Lynx, one of the four strategic mission concepts under study for the 2020 Astrophysics Decadal Survey, provides leaps in capability over previous and planned x-ray missions and provides synergistic observations in the 2030s to a multitude of space-and ground-based observatories across all wavelengths. Lynx provides orders of magnitude improvement in sensitivity, on-axis subarcsecond imaging with arcsecond angular resolution over a large field of view, and high-resolution spectroscopy for point-like and extended sources in the 0.2-to 10-keV range. The Lynx architecture enables a broad range of unique and compelling science to be carried out mainly through a General Observer Program. This program is envisioned to include detecting the very first seed black holes, revealing the high-energy drivers of galaxy formation and evolution, and characterizing the mechanisms that govern stellar evolution and stellar ecosystems. The Lynx optics and science instruments are carefully designed to optimize the science capability and, when combined, form an exciting architecture that utilizes relatively mature technologies for a cost that is compatible with the projected NASA Astrophysics budget. © The Authors. Published by SPIE under a Creative Commons Attribution 4.0 Unported License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its DOI.

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