Top row: light curves of a target 3 single pixel showing transient brightening before (a) and after (d) the processing described in Sect. 2. In this and subsequent light-curve displays, the arrows indicate the times in which the intensity exceeds the 2.5σ threshold above average. Middle row: same as top row for a pixel that did not show transient brightening. The curve in panel b has been displaced by −300 K. Bottom row: panel c shows the power spectra deduced from light curves (a) and (b), while panel f shows the power spectra deduced from light curves (d) and (e).