A HIGH-RESOLUTION X-RAY-SPECTRUM OF CENTAURUS X-3

The high-mass X-ray binary pulsar Centaurus X-3 was observed with the Broad Band X-Ray Telescope (BBXRT) in 1990 December as part of the Ast ro-1 mission on the Space Shuttle Columbia. During the similar to 1600 s observation, the system was in a high-luminosity postegress state. With an energy resolution of about 150 eV FWHM at 6 keV, the Fe K emis sion feature was resolved into at least two components. We found a bro ad (similar to 740 eV FWHM) emission feature at 6.7 keV which is proba bly a blend of lines from Fe XXI to Fe XXVI due to X-ray photoionizati on of the stellar wind of the companion. This is the first time the ph ysical width of the 6.7 keV feature has been measured in Cen X-3. We a lso found evidence for a weak emission line at 6.4 keV with no discern ible width, which we attribute to fluorescence of iron in relatively l ow ionization states. We did not detect pulsations in the iron emissio n features, but our sensitivity does not rule out the presence of puls ations with 50% amplitude as reported by Day et al. in 1993. We confir m. the presence of quasi-periodic oscillations at about 40 mHz.