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B. J. Teegarden (NASA/GSFC)
One of the primary goals of the spectrometer (SPI) on the INTEGRAL mission is detailed mapping and spectroscopy of the Galactic electron-positron annihilation radiation. The INTEGRAL coded-aperture array and high-resolution germanium detectors are optimized to resolve the spectral components and map the Galactic distribution of this emission. INTEGRAL has found that the bulk of the radiation is concentrated towards the center of our Galaxy. It can be well-described by a symmetric gaussian with a FWHM of 8 degrees. Evidence for a more extended Galactic Plane component is emerging from the data (currently at the 3-4 sigma level). The data are generally consistent with the earlier results from the CGRO/OSSE mission However, the so-called ``Galactic fountain" (an enhanced region of emission above the Galactic Plane reported in early analyses of the CGRO/OSSE data) is not seen. INTEGRAL detects the 3-photon positronium annihilation continuum and finds that its morphology is similar to the 511-keV narrow-line distribution. Recently, evidence has been found for a 2-component structure for the 511 keV line, a narrow component (FWHM ~ 1 keV) and a broadened component (FWFM ~ 5 keV). The latter expected from the 2-photon decay of positronium in flight. The spectroscopic results are consistent with the annihilation taking place in the warm, partially-ionized phase of the interstellar medium.
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Bulletin of the American Astronomical Society, 37 #4
© 2005. The American Astronomical Soceity.