Is GX 1+4 the Compact 511 keV Galactic Center Source?

An intense 511 keV positron annihilation-line source was detected from the direction of the Galactic center throughout the 1970s. The source disappeared abruptly early in the 1980s. It remained in a low state through at least 1984 and reemerged 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 GX 1+4. The similar light curves of the two sources, coupled with their positional agreement and the unusual properties of GX 1+4, suggest that GX 1+4 is the Galactic center positron/511 keV source.