Time delays of the eclipse arrival times with respect to the linear ephemeris of Hellier & Smale (1994). The black open squares correspond to the eclipse arrival times shown by Hellier & Smale (1994) and PA00, the red diamonds to the Chandra eclipse arrival times given by JI11, the green filled squares to the Chandra eclipse arrival times reported in this paper (see Table 3), the blue open circles to the Chandra eclipse arrival times reported by BU10. The dashed and solid lines are the best-fit quadratic curve obtained by JI11 and in this paper (see text), respectively. (This figure is available in color in the electronic form.)