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Fig. A.3


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.

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