Top: O–C diagram of the mid-eclipse times relative to the linear ephemeris of Eq. (1). The difference between the quadratic and linear ephemerides of Eqs. (2) and (1) is shown as the dashed curve. Second from top: FWHM of the eclipse vs. pulse phase from Eq. (6). Center: O–C values of the mid-eclipse times relative to the quadratic ephemeris vs. pulse phase. The model curve is from Eq. (4) (see text). Second from bottom: O–C diagram for the minimum times of the 65-minute pulsations relative to the linear ephemeris of Eq. (6). Bottom: O–C values of the previous graph vs. orbital phase (see text).