Source best-fit parameters as a function of MJD (EPIC analysis; see text and Tables 5 and 6 for details). The model fit to the data is that of absorbed double-blackbody (left) and fully ionized hydrogen neutron star atmosphere (B = 10¹³ G, M = 1.4 M_⊙, and R = 10 km; right), modified by a broad Gaussian absorption line. The plots show in each instrument and observation (see legend): panel a: column density, temperature of the (panel b) cold and panel c: hot blackbody components, panel d: effective temperature of the neutron star (unredshifted), panel e: central energy of the absorption line, panel f: its Gaussian sigma, and panelg: observed model flux in the 0.2–12 keV energy band. The total Galactic N_H value is shown by the solid black line in plots (panel a). Horizontal lines show the results of the simultaneous fit of spectra over the five pointings, with 1σ confidence levels comprised by the shaded areas.