X-ray Loading, Gainshift & (Modified) Timing Mode of XMM-Newton’s EPIC-pn

Abstract

Knowing the instrument’s behaviour is highly important when analyzing the collected observational data. Here we investigate the issue of the energy gainshift associated with the EPIC-pn instrument on-board XMM-Newton, when it is operated in Timing mode. The gainshift arises as a result of CTI effects or X-ray loading. This depends on the source brightness and the effectiveness of the noise correction. X-ray loading has clearly been detected in Imaging mode, while the importance of its impact on the Timing mode observations is still under investigation. The consequences of X-ray loading in general are pattern migration from higher to lower pattern types and a shift to lower energies for all events associated with the affected CCD column. Current results show a clear correlation between X-ray loading and X-ray flux of the source, but other correlations may also reveal ways to understand and correct for the energy gainshift in the data. A pequliar case of Timing mode is the Modified Timing mode, and here we also explain its properties and its potential impact on the scientific results dealing with bright X-ray sources.