0220114

We propose to carry out an INTEGRAL survey of Sgr A* simultaneously with the approved XMM-Newton large project (552 ks) exposure monitoring program of the galactic nucleus and the associated multiwavelength campaign planned for 2004. The primary aim of this program is a detailed study of the X-ray/gamma-ray activity of Sgr A* the radiative manifestation of the massive black hole at the galactic center. Although the galactic nucleus hosts the nearest and probably best studied massive black hole its physical and radiative properties and in particular its low level of high energy emission remain little understood. The discovery of bright and hard X-ray flares from SgrA* with Chandra and XMM-Newton in the last two years has certainly opened new perspectives in understanding the processes at work in accreting black holes but a number of crucial questions remain unaswered. Recent INTEGRAL observation of the Galactic Center have led to the discovery of a significant excess at energies > 20 keV in direction of the Sgr A complex. This excess appears to be variable and it is probably associated with the activity of Sgr A*. Simultaneous observations of Sgr A* with INTEGRAL and XMM-Newton will allow to verify the association of the INTEGRAL source with Sgr A* and thus to provide a measure of the gamma-ray emission from the galactic nucleus. The broad band data that will be obtained through this program especially if coupled to simultaneous infrared and sub-mm observations will be invaluable in assessig the validity of the principal emission models for Sgr A* i.e. boosted jets or accretion flow and in understanding other issues related to low accretion rates in compact objects. The Sgr region has already been observed with INTEGRAL in 2003 and it will be observed again in the course of the GCDE in 2004. However the herein proposed program requires performing the INTEGRAL observations simultaneously to the planned XMM ob [truncated! Please see actual data for full text]