Top panel: spline fit of the ECAM data of SDSS J1226−0006. The black line represents the intrinsic variation shared by both curves (η = 45 days) whereas the blue and orange lines model the extrinsic variations of A and B, respectively (η_ml = 300 days). The curves are shifted in time by the optimal time delay, and corrected from their modelled extrinsic variations. Middle panel: residuals of the spline fit. Bottom panel: regression fits using Gaussian processes and their 1σ envelopes. The difference curve between the regression curves fitted on image A and image B is also shown in black. The algorithm is optimising the time shift in order to minimise the variability in the difference curve.