Spring, 1997 Granat/Sigma Observations Of The Galactic Center: Discovery Of The X-Ray Nova Grs 1737-31

The results of GRANAT/SIGMA hard X-ray observations of the Galactic center in March, 1997 are reported. One new source - GRS 1737-31 and two previously known sources - 1E 1740.7-2942 and GRO J1744-28 were detected. The spectral and temporal behavior of GRS 1737-31 suggests that this source may be a distant X-ray Nova and a black hole candidate.The comparison of the hard X-ray transient detection rates by GRANAT/SIGMA and currently operating all-sky monitors (CGRO/BATSE, GRANAT/WATCH) leads to following conclusions regarding the spatial and luminosity distributions of the hard X-ray transients:(i) the spatial distribution of X-ray Novae exhibits a concentration towards the Galactic Center similar to the distribution of the visible matter in the Galaxy. In particular, it is more concentrated than Galactic disk population.(ii) if hard X-ray transients follow distribution of visible mass in the Galaxy then their peak luminosity in the 35-150 keV band is close to 10(37) ergs(-1) with a relatively small scatter.