As in Fig. B.2, but for the combined Chandra data obtained from MJD 58157–58180. We note the difference in the 50% contour of the pulsed fraction (and the χ²) compared to Fig. B.2. This is an effect of the time gap between the observations. In the case of Swift/XRT due to the observational gaps and the low number of counts it is not possible to derive a unique solution in the P vs. Ṗ plane. The goodness of fit (i.e. χ²) is computed by using ten phase bins for the folded pulse profile.