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

TL;DR

This paper updates a model of radiation damage in the Hubble Space Telescope's camera, showing increased charge traps affecting image quality and demonstrating a method to correct for this trailing effect.

Contribution

It presents a robust, temperature- and background-insensitive model of charge transfer inefficiency and a correction technique to restore image quality.

Findings

Charge traps increased to ~1.3 per pixel before Servicing Mission 4.

The correction method effectively restores image quality to early mission levels.

Model robustness allows for iterative trailing removal in data processing.

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.