Persistence And Count-Rate Non-Linearity In The Hst Wfc3 Ir Detector

We now know that the flux of a source measured with HgCdTe arrays is not a simple, linear function, but depends on the count-rate as well as the total number of counts. In addition to the count-rate non-linearity (and probably related to the same physical mechanism), HgCdTe detectors are also susceptible to image persistence. Most of the persistence image fades in a few minutes, but there is a longer-term component that can result in faint afterimages in the next orbit, approximately 45 minutes later. For sources saturated at similar to 100 times full-well, the afterimages can persist for hours afterwards. This report describes results from ground and on-orbit tests to characterize the persistence and the count-rate non-linearity in the WFC3 IR detector during its first year of operation.