LONG-TERM TEMPORAL BEHAVIOR OF 1E 1740.7-2942

After more than 3 years of performances, the French gamma-ray telescop e SIGMA on board the Russian spacecraft Granat has recorded approximat ely 1000 hr of data on the Galactic center (GC). This survey of the GC is the lengthiest ever made with the same instrument in this energy r ange, and it allows a consistent study of the singular source 1E 1740. 7-2942. These unprecedented observations, combined with previous ones, reveal a complex temporal behavior of 1E 1740.7-2942. These observati onal results imply some constraints on the nature of this object.