Hard X-Rays from the Galactic Nucleus: Present and Future Observations

Abstract

In spite of increasing evidences of the presence of a massive Black Hole at the Galactic Center, its radio counterpart, Sgr A*, shows little activity at high energies, and recent models involving energy advection (ADAF) have been proposed to explain this difficulty. We present results on the hard X-ray emission from the galactic central square degree obtained from the SIGMA/GRANAT 1990-1997 survey of this region. The best upper limits available today on the Sgr A* 30-300 keV emission are presented and compared to X-ray data and to the predictions of ADAF models. We also present simulations of Sgr A* observations with the future ESA gamma-ray Observatory INTEGRAL, which show that the imager instrument (20 keV-10 MeV) will be able either to detect the expected ADAF emission from the accreting Galactic Nucleus black hole or set tight upper limits which will constrain the physical parameters of such system.