K2 photometric light curve after the removal of known unphysical spurious signals. The two transits of K2-18b are highlighted by the ong blue ticks with the expected times of mid-transit for K2-18c highlighted with short green ticks (see Sect. 5). The solid yellow curve is the mean of the predictive GP distribution and the surrounding shaded regions mark its 99% confidence intervals. The upper left sub-panel is a magnified view of the highlighted region to aid in the visualization of the data and the GP fit.