Light curve and pulse profile of the X-ray pulsar VELA X-1.

Features of the light curve and pulse profiles of the eclipsing X ray binary Vela X-1 are detected with the honeycomb collimator on board the Hakucho satellite are discussed. Light curves are presented for the 1-9 keV and 9-22 keV energy ranges. An energy dependence was noted in the width of the X ray eclipse, and a relationship is defined between the softness ratio and the absorption measure. Differences in the pulse profiles at the two energy levels are taken to indicate absorption by cold matter, which may be in the accretion column. The absorber is the stellar wind, which has a flow pattern in the X ray energy ranges studied that corresponds with visual observations. An orbital period of 8.9640 days is obtained, in line with previous estimates. The accreting matter, being heated, may be responsible for the X rays observed.