WFC3/IR Spatial Sensitivity Test

Here we present details on the WFC3/IR spatial sensitivity test. The aim of the test is to observe a standard star in a grid pattern covering the IR detector to investigate spatial variations in the measured photometry. Any deviations from a uniform response could be due to errors in the flat field calibration file. We find that the current pipe-line IR flat-fields, which are a combination of a ground-based high frequency (pixel-to-pixel) component and a low frequency correction based on in-flight sky observations, produces stable photometry over most of the detector. We estimate that the typical rms in measured photometry due to the flat field uncertainties is less than ∼0.007 mag. We do not find any significant low frequency large scale gradients in the photometry, except possibly for a region near the bottom left of the detector. Overall, these test indicates that the IR flat fields produce consistent photometry over the central 800x800 pixels of the detector investigated here.