The Galactic Centre (GC) is one of the most observed region at X/gamma wavelengths. New sources appear very frequently. For instance, 11 sources were discovered during 1988-90 by the instruments onboard MIR and GRANAT [72]. The high variability of the GC region, and the fact that satellites like GRANAT or INTEGRAL only can monitor the GC during Spring and Autumn, underlines the importance of having an instrument with the capability of performing frequent observations of this region. This can be done with XTEL any time from February to October.
Moreover, a considerable fraction of the Galactic plane can be surveyed in pointings spaced 10 degrees in galactic longitude. In 600 s exposure time, sources as faint as 25 mCrab can be detected. Such a survey will occupy about 20 % of the daily observing time.