We present the study of the aperiodic time
variation of the binary X-ray pulsars observed with
the Rossi X-Ray Timing Explorer, (RXTE).
The iron K lines observed from X-ray pulsars is thought
to be a fluorescenct lines and considered to come from
a re-processing matter around the neutron star.
Thus the X-rays in the energy band containing the iron K
lines is expected to have a certain delay from the higher
energy X-rays. We have discovered that the
temporal variation of iron-band emission is delayed as
compared with that of the other energy X-rays. We also
have discovered that higher X-rays are advanced
in comparison with the lower energy X-rays in some X-ray
binary pulsars.
We will present our detail analysis by using cross spectra
and discuss the implications of our results. |