Persistence in the 16 VIRCAM detectors. The figure is based on a number of image pairs taken right after each other, called image 0 and image 1. Only subsections with a somewhat bright star in image 0 and no astronomical object in image 1 were analysed (the telescope moved in between the two images). In each image the median value over the image, i.e. the background, was subtracted. For each pixel, the fluxes f₀ and f₁ in the two images were measured. The figure shows a plot of these, binned in f₀. The persistence (i.e. detector memory effect) is seen by the fact that f₁ becomes positive above a certain threshold in f₀. The black solid line is a fit to the data (Eq. (A.1)). The red dashed line is the threshold in f₀ at which the fit reaches a value of 3 ADU above the background, and this is used in our masking algorithm as the threshold for masking a given pixel (i.e. for excluding it when stacking the data). For detector 5 a lower threshold was manually set, as indicated by the blue dot-dashed line. The used thresholds are given on the panels and listed in Table A.1. The f₀ axis is logarithmic and runs from 10 to 70 000. The units are gain-normalised ADU, as used in the individual images reduced by CASU.