1. Motivation

The results of Chapter 5 indicated that pulse and orbital phase-resolved spectroscopy of Cen X-3 outside of X-ray eclipse would be useful. Previous observations had shown that several Fe K lines were present; a 6.4 keV line emitted from a region within 1 lt-sec of the neutron star and lines at 6.7 and 6.9 keV probably emitted from over much of the binary system. At least one of the lines was modulated at the 4.8 sec pulse period, but it was not possible to tell which one. Using the SIS to observe from orbital phase 0.2-0.8 it might be possible to determine which lines are modulated and physically locate the sites of the X-ray emission components in a massive X-ray binary for the first time.