Deep SIGMA observations of the central square degree of the Galaxy

The Center of the Milky Way emits radiation through all the electromagnetic spectrum due to the presence of several astrophysical phenomena. Various s cientifical questions remain unsolved in the picture that emerge from obser vations, the main one being the presence and activity of a supermassive bla ck hole at the Galactic Center. Also in the X-ray band a strong diffuse emi ssion is detected up to 22 keV, it has been suggested that its origin is li nked to past high energy activity of the Galactic Center. The French SIGMA soft gamma ray telescope on board the Russian Granat satellite observed the Galactic Center (GC) for about 9 X 10(6) seconds from 1990 to the end of 1 997. Its unique imaging capabilities coupled with the unprecedented exposur e already allowed us to set preliminary constraints on the persistent high energy emission from Sgr A*. Here we present a new analysis of the complete set of observations of this region taking into account the possible presen ce of diffuse emission in the low energy channels. This allows us both to t est current advection models of high energy emission from SgrA* and to inve stigate on past high energy activity.