3. The pulse profile

The average pulse profile consists of two peaks of similar size separated by $\sim110\hbox{$^\circ$}$
. Figure 3.3 shows the folded intensity and hardness profiles for different orbital phases. The factor of four change in the X-ray intensity through the observation is accompanied by significant changes in the pulse profile. The profile also has different energy dependence at different orbital phases.

Figure 5: Orbital phase resolved GIS pulse profiles and hardness ratios. The upper panel is the 0.7-11 keV intensity divided by the pulse-phase average. The lower panel is the ratio of the 0.7-4.5 keV count rate to the 4.5-11 keV count rate.