TGRS Observation of the Galactic Center, Annihilation Line

B. J. Teegarden(1,5), T. L. Cline(1), N. Gehrels(1), D. Palmer(1), R. Ramaty(1), H. Seifert(1), K. H. Hurley(2), D. A. Landis(3), N. W. Madden(3), D. Malone(3), R. Pehl(3), and A. Owens(4)

(1) NASA/Goddard Space Flight Center (2) University of California, Berkeley (3) Lawrence Berkeley Laboratories (4) University of Leicester (5) On leave at Centre d'Etudes Spatiale des Rayonnements, Toulouse

Paper: to appear in ApJ, 463, L75



The TGRS (Transient Gamma-Ray Spectrometer) experiment is a high-resolution germanium detector launched on the WIND satellite on Nov. 1, 1994. Although primarily intended to study gamma-ray bursts and solar flares, TGRS also has the capability of studying slower transients (e.g. x-ray novae) and certain steady sources. We present here results on the narrow 511 keV annihilation line from the general direction of the Galactic Center accumulated over the period Jan. 1995 through Oct. 1995. These results were obtained from the TGRS occultation mode, in which a lead absorber occults the Galactic Center region for 1/4 of each spacecraft rotation, thus chopping the 511 keV signal. The occulted region is a band in the sky of width 16\arcdeg that passes through the Galactic Center. We detect the narrow annihilation line from the galactic center with flux = (1.64 +/- 0.09)*10^-3 ph cm^-2 s^-1. The data are consistent with a single point source at the galactic center, but a distributed source of extent up to ~30 arcdeg cannot be ruled out. No evidence for temporal variability on time scales longer than 1 month was found.

Preprints available from the authors at , or the raw TeX (no figures) if you click here.

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