SIMBAD references

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 preliminary results on the narrow 511keV annihilation line from the general direction of the Galactic Center. These results were obtained from the TGRS occultation mode. In this mode a lead absorber occults the Galactic Center region for 1/4 of each spacecraft rotation, effectively chopping the signal. Data are presented here for the first 2 months of 1995. We detect the narrow annihilation line from the galactic center with flux=(1.36±0.2)x10^–3cm^–2/s, and width (FWHM)=2.6(+1.0/-0.3)keV. The data are consistent with a single point source at the galactic center, but a distributed source of extent up to ∼15° cannot be ruled out. No evidence for temporal variability on time scales longer than 1-month was found.