Is GX1+4 the Compact 511 keV Source in the Galactic Center?.
01 January 1989
An intense 511 keV positron annihilation-line source was detected from the direction of the galactic center throughout the 1970's. The source disappeared abruptly early in the 1980's. It remained in a low state through at least 1984, and re-emerged sometime between 1984 and 1988. This "on-off-on" light curve is mimicked by the X-ray light curve of the pulsating X-ray binary GX1+4. The similar light curves of the two sources, coupled with their positional coincidence and the unusual properties of GX1+4, suggests that GX1+4 is the galactic-center positron/511 keV source.