  The long-term X-ray lightcurves of classical supergiant X-ray binaries and
supergiant fast X-ray transients show relatively similar super-orbital
modulations, which are still lacking a sound interpretation. We propose that
these modulations are related to the presence of corotating interaction regions
(CIRs) known to thread the winds of OB supergiants. To test this hypothesis, we
couple the outcomes of 3-D hydrodynamic models for the formation of CIRs in
stellar winds with a simplified recipe for the accretion onto a neutron star.
The results show that the synthetic X-ray light curves are indeed modulated by
the presence of the CIRs. The exact period and amplitude of these modulations
depend on a number of parameters governing the hydrodynamic wind models and on
the binary orbital configuration. To compare our model predictions with the
observations, we apply the 3-D wind structure previously shown to well explain
the appearance of discrete absorption components in the UV time series of a
prototypical B0.5I-type supergiant. Using the orbital parameters of
IGRJ16493-4348 which has the same B0.5I donor spectral type, the period and
modulations in the simulated X-ray light-curve are similar to the observed
ones, thus providing support to our scenario. We propose, that the presence of
CIRs in donor star winds should be considered in future theoretical and
simulation efforts of wind-fed X-ray binaries.
