Top panel: a comparison of the observed signal of a single spectral pixel (cyan) with the Guess signal (blue; see text). The signal is plotted against the Frame Number, which is a function of time during the scan. We show three scans in the figure (two up and one down) which captures the C+ line shown in the previous figure. Just after the frame number 4720 a strong cosmic ray hits the detector producing a sudden change of the response of the detector. Bottom panel: the ratio of the two curves, i.e. the response of the pixel as a function of frame number. Many transients are clearly visible, in particular the huge transient after frame number 4720.