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Sink pixels in the HST wide-field channel 3 CCDs

Isolated pixels with anomalously-low signal in otherwise normal Hubble Space Telescope Wide-Field Channel 3 (HST/WFC3) CCD data have been dubbed 'sink pixels' or SPs. The SPs appear to contain an exceptionally large number of charge traps and thus, they capture a commensurate amount of charge during readout. The effects of the sinks on science data depend on a number of factors including the image background, SP distance from the amplifier, and data epoch. In images with high backgrounds, the sinks act as essentially negative delta-functions, impacting a relatively small number of pixels. In contrast, in images with low backgrounds, the sinks can remove charge from a significant number of trailing pixels generating trough-like profiles. In this paper, we characterize the sink pixels, evaluate their effect on science data, and summarize how the sinks are flagged in the calibration pipeline.