Evolution of temperature-dependent charge transfer inefficiency correction for ACIS on the Chandra X-ray Observatory

摘要

As the Advanced CCD Imaging Spectrometer (ACIS) on the Chandra X-ray Observatory enters its seventeenth year of operation, it continues to perform well and produce spectacular scientific results. The response of ACIS has evolved over the lifetime of the observatory due to radiation damage and aging of the spacecraft. The ACIS instrument team developed a software tool which applies a correction to each X-ray event and mitigates charge transfer inefficiency (CTI) and spectral resolution degradation. The behavior of the charge traps that cause CTI are temperature dependent, however, and warmer temperatures reduce the effectiveness of the correction algorithm. As the insulation on the exterior of the spacecraft degrades with time, the temperature of the ACIS focal plane can increase by several degrees for some spacecraft orientations. A temperature-dependent component was added to the CTI correction algorithm in 2010. We present an evaluation of the effectiveness of this algorithm as the radiation damage and thermal environment continue to evolve and suggest updates to improve the calibration fidelity.