2 outbursts last for several orbital cycles (e.g. V0332+53, [@Ste86]). The phasing of this outbursts should be dictated mainly by the time variability of the Be star mass outflow rate. It is still unclear what causes the giant outbursts. They may be observed if the circumstellar disk undergoes a sufficiently large increase in its radial extent and density to intersect the NS orbital path. If a disk can be sustained between giant outbursts, it may be also present during normal outburst. In this case the large tidal torque experienced by the disk during periastron passage could explain the repeating normal outburst [@Bil97]. Not far ago it was proposed that the thermal disk instability like one causing dwarf nova outbursts affect accretion disk around Be X-ray pulsars and could be the cause of the giant outburst [@VanPar96; @Kin96].

The pattern of X-ray outbursts is affected by the size, eccentricity and orientation of the NS’s orbit with respect to the Be star. The orbit could be complanar with the Be star circumstellar disk or offset such a way that the NS may pass through the disk. In some case the consequent outbursts can have different intensities (e.g. XTE J1946+274, [@Cam99] ). This 