A TURBULENT MODEL OF TIME VARIABILITY IN X-RAY BINARY PULSARS

It is found that the observed power spectral density of the aperiodic time variability of the X-ray pulsar can be approximated by a power-law spectrum which changes its slope at the pulsation frequency (pulsar rotation frequency). The indices of the observed spectra are, respectively, 1.4-2.0 above the pulsation frequency and 0-1.0 below the pulsation frequency. By studying the density fluctuation spectra with inverse cascades in magnetohydrodynamic turbulence, we find that the observed X-ray spectra can be interpreted as the density fluctuations in the accreting plasmas. It is shown that the structure of either disk-fed or wind-fed pulsars can be determined by comparing the observed X-ray spectra with the theoretical density fluctuation spectra of two- or three-dimensional magnetohydrodynamic turbulence, respectively.