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Cross-Talk in the ACS WFC Detectors. I: Description of the Effect

Images acquired with the Wide Field Channel (WFC) of the Advanced Camera for Surveys (ACS) are affected by cross talk between the four CCD quadrants that correspond to the four amplifiers of the detector array. The effect is observed as (mostly) negative ghost images generated by relatively bright sources located in adjacent quadrants. Their position in the quadrant is mirror-symmetric relative to the positions of the generating sources. The strength of the cross talk is small, i.e. the ghost images have apparent surface brightness of only a few electrons per pixel, and it appears to be mostly a cosmetic problem, with little measurable effects on the photometry of affected sources. Here we describe the phenomenology of the cross talk, and in a companion ISR (Giavalisco 2004) we suggest an observing strategy to minimize its effects on the images.