A long-term observation of 4U 1700-37 by the granat/watch all-sky monitor

We present the results of the observations of the X-ray source 4U 1700-37 by the WATCH all-sky monitor on GRANAT during the period 1991 to 1992. We have reconstructed light curves of 4U 1700-37 in two energy bands which prove the strong variability of the source's intensity on various time scales. The light curve having been folded with the orbital period clearly reveals a dependence of the source's intensity upon the orbital phase.

This dependence can be explained by scattering and absorption of photons in the stellar wind of the massive optical companion. We interpret the X-ray light curves with the help of Monte-Carlo simulations and derive the basic parameters of the stellar wind. We show that the wind in 4U 1700-37 well fits in the radiatively driven stellar wind theory.

Our measurement of the mid-eclipse time together with the measurements of other experiments imply a decrease in the period of the binary.