Search for the compact 511 keV radiation source in the Galactic Centre region with SIGMA.

Results of a search for the compact 511 keV radiation source in the general region of the Galactic center (GC) with SIGMA are presented. No evidence of any compact 511 keV radiation source in the region was found. The combined 2-sigma upper limits for the three possible candidate sources are listed. These upper limits are far below the steady 0.0027 gamma/s sq cm 511 keV flux observed by SMM, assuming that it came from a point source in the GC region. They thus rule out the possibility of a single point source for the emission of the GC 511 keV radiation. A reanalysis of HEAO-3 data shows that, if the instrumental line width of the observed GC 511 keV line is taken into account, the fall 1979 and spring 1980 fluxes are consistent with the SMM. A diffuse solution to the GC 511 keV radiation is inferred.