LMXBs and black hole candidates in the Galactic Center region

The central part of the Galactic Plane has been intensively observed by GRANAT/SIGMA in 1990–1994. At least 11 sources are seen on the averaged 35–100 keV image of this region, most of them being low mass X-ray binaries. With GRANAT/SIGMA observations the X-ray bursters are recognized as sources emitting hard X-rays (up to ∼ 100 keV) during substantial fraction of time. This “bimodal” behavior (soft and hard spectral states) of X-ray bursters resembles that of black hole candidates (BHC), although unlike BHCs soft state for the bursters seems to be the dominant one. On average the spectra of bursters in the SIGMA energy band (above 35 keV) were found to be steeper than that of BHCs. This difference is discussed in terms of Comptonization model.