  We have obtained spectra of the Galactic center at energies 400-600 keV from
high-resolution data acquired by the TGRS Ge spectrometer on board the WIND
mission during 1995-1997. The data were obtained using an on-board occulter,
and are relatively free from systematics and backgrounds. Analysis of the
spectra reveals a well-resolved electron-positron annihilation line at 511 keV
and the associated continuum due to annihilation via positronium formation.
Measurements of the line width and the line-to-continuum ratio allow some
constraints to be placed on the interstellar sites where annihilation occurs.
