PULSE PHASE-DEPENDENT SPECTROSCOPIC STUDY OF VELA X-1

We analyzed the X-ray observations of Vela X-l obtained with the Ginga large area counter (LAG) on 1991 August 18-19. During the observation s, which cover orbital phase Phi(orb) = 0.29 - 0.47, we detected an in tensity dip at Phi(orb) = 0.33 - 0.38. The pulse amplitude of the X-ra y flux was much reduced in the dip and was almost invisible in lower e nergy band. From the spectroscopic study, clear modulation of the iron Line flux with the pulse period was observed at the half-amplitude of 10% during the dip. We also detected modulation of the iron line cent er energy in the data set obtained at Phi(orb) = 0.43 - 0.47. These ph enomena may be explained by the X-ray reprocessing in the accretion wa ke.