was made. The count rates for X-ray photons were measured over the energy ranges of 10-50, 25-50, 50-100, 100-200 keV. The region of the sky that was observed during the experiment is shown in equatorial coordinates in Fig 1. The points of the sky toward which the satellite’s axis was pointed at different times (the dates in the figure refer to the origin of the corresponding intervals of constant orientation) are also marked in this figure. The main X-ray transient pulsars and the Galactic equator are shown. During the observations from November 1983 to February 1984 of the sky region near the Galactic Centre (outlined by the closed solid line in Fig. 1), the count rates were considerably higher than the background count rates. Since each source in that region can be observed as long as 100 days, while virtually continuous measurements of count rates averaged over 10 s were made, the experiment provided favorable conditions for the study of periodic events over a wide range of periods.

The long-term observations of the Galactic Center region as well as of some other sky regions were also conducted during the GRIF experiment on-board “Mir” orbital station (mean altitude $\sim 400$ km, 