The Zoo of X-Ray Sources in the Galactic Center Region: Observations with BeppoSAX

摘要

We report the results of a survey of the Galactic center region ( l 2°, b 05) performed with the BeppoSAX satellite. The flux from the center of our Galaxy corresponds to a luminosity of ~3 × 1035 ergs s-1 in the 2-10 keV range. Due to the limited angular resolution (1'), only part of it is supposed to come from Sagittarius?A*, the nonthermal radio source that is believed to mark the dynamical center of the Galaxy. In addition to the diffuse emission, several bright (LX 1036?ergs?s-1) point sources have been observed, both persistent (A1742-294, SLX?1744-299, SLX?1744-300, 1E?1743.1-2843, 1E?1740.7-2942) and transient (XTE?J1748-288, SAX?J1747.0-2853 and KS?1741-293). The low-mass X-ray binary (LMXRB) AX J1745.6-2901, discovered with ASCA at only 13 from Sgr A*, was detected in a low-luminosity state in 1997 August. The 1-150 keV spectrum of the hard X-ray source 1E?1740.7-2942 is well described by a Comptonization model, typical of black hole candidates in their low/hard state, with no evidence for strong Fe lines. The detection of a type I burst shows that the transient source SAX?J1747.0-2853 (probably the same as the 1976 transient GX 0.2-0.2) is a LMXRB containing a neutron star. The transient black hole candidate XTE?J1748-288 was detected at a luminosity (~1036?ergs?s-1) consistent with the extrapolation of the exponential decay of the outburst observed with the XTE All-Sky Monitor. Two fainter sources are very likely associated with young neutron stars: the (possibly diffuse) X-ray source at the center of the composite supernova remnant G0.9+0.1, and the "head" of the axially symmetric radio source G359.23-0.92. The latter has been detected above ~6 keV, supporting a nonthermal emission mechanism.