On the estimate of the stellar wind velocity of the massive components in X-ray binary systems

We discuss manifestations of the wind-fed accreting pulsars in the massive X-ray binary systems. We point out that the X-ray luminosity of a pulsar in this case depends on the mass capture rate by a neutron star from the wind of its massive component. The key parameter constraining the mass capture rate is the relative velocity of the neutron star with respect to the wind outflowing in the orbital plane of the binary system. We show that the observed luminosity of the X-ray pulsars in these systems can be explained under condition that the velocity of stellar wind of the massive component in the orbital plane of the system does not exceed 1000 km/s, while the mean value in most cases is in the interval 300–600 km/s.