1. Background Subtraction

The data had barycentric corrections and orbital motion corrections applied before being extracted into twenty pulse-phase resolved spectra. The pulse-phase average spectra were also extracted. For the 1985 May data the slew spectrum was used as background. The background subtraction is acceptable between 2 and 25 keV and this was the energy range chosen for spectral fitting. For the 1985 August data we used the standard blank sky background because of a lack of good slew data. In this case the subtraction was worse and the energy range for fitting was restricted to 3-24 keV.