NS itself and of binary system components produce pulsation, orbital and super-orbital periodic changes in X-ray source luminosity. X-ray pulsations with pulse period of about dozens and hundreds seconds were clearly detected. Long-term variability of most of transient pulsars appears as their flaring activity.

The most of transient X-ray pulsars have Be (or Oe) star companions. Accreting NSs in Be systems typically have long periods and eccentric orbits. It is to be thought, that the source of accreting material is the slow, dense stellar wind, presumably from the circumstellar disk confined to the equatorial plane of the rapidly rotating Be star. The Be-transients display a marked correlation between their spin and orbital periods. This correlation arises from the fact that given identical companion masses and mass loss rates, NSs in binary systems with lower orbital periods are further away from their companions, these leading to lower mass accretion rates and higher equilibrium periods [@Bil97]. Various instabilities in the accretion process lead to the flaring activity of some kind of X- ray pulsars. It is known that X-ray behavior of Be transient pulsars is characterized by regular increases of the X-ray flux modulated with the orbital period. Such recurrent flares (type 