Charge Transfer Inefficiency in the Hubble Space Telescope since Servicing Mission 4

Abstract: We update a physically-motivated model of radiation damage in the Hubble Space Telescope Advanced Camera for Surveys/Wide Field Channel, using data up to mid 2010. We find that Charge Transfer Inefficiency increased dramatically before shuttle Servicing Mission 4, with ~1.3 charge traps now present per pixel. During detector readout, charge traps spuriously drag electrons behind all astronomical sources, degrading image quality in a way that affects object photometry, astrometry and morphology. Our detector readout model is robust to changes in operating temperature and background level, and can be used to iteratively remove the trailing by pushing electrons back to where they belong. The result is data taken in mid-2010 that recovers the quality of imaging obtained within the first six months of orbital operations.