WFC3 Thermal Vacuum Testing: UVIS Crosstalk

The integrated WFC3 instrument recently underwent testing under thermal vacuum (TV) conditions in the GSFC SES (Goddard Space Flight Center Space Environment Simulator). This report summarizes the behavior of the UVIS channel crosstalk features seen in the TV data as compared to the behavior seen in previous data taken under ambient conditions in early 2004 and provides an update on the hardware investigation underway at the Detector Characterization Lab (DCL) at GSFC . The crosstalk in the TV images has been found to be essentially identical to the crosstalk in ambient images: 1) levels are low, +/a few DN on average though individual pixels can exhibit crosstalk up to +/-10DN, 2) the effect is highly nonlinear, 3) the crosstalk is bias and gain dependent, and 4) the behavior of the crosstalk as a function of binning and readout combination remains unchanged. The hardware testing at DCL has found that the CEB test set and the flight-like harness generate crosstalk which does not behave exactly like the crosstalk in the flight channel. Further investigation into the cause of the crosstalk will require use of the flight hardware.