RANDOM VARIATIONS OF THE PULSE PERIOD OF X-RAY BINARIES WITH WIND ACCRETION

In this paper we first summarise earlier results about the randomness of pulse period variations in wind fed X-ray pulsars. Then we present two types of models for the random spin-up and spin-down of rotating n eutron stars which accrete mass from a stellar wind. We show that the irregularities in accretion flows which were discovered in numerical m odels have too low amplitudes in order to explain the observations. Th erefore we discuss an alternative model which is based upon the existe nce of a Kepler disc around the neutron star. We argue that such a mod el can give an explanation of the observations.