X-Ray Loading (XRL) occurs whenever source counts contaminates the offset map taken prior to each EPIC-pn exposures. Instrument operations have been configured in such a way that XRL should never occur, if the appropriate combination of instrument mode and filter is selected based on the brightness of the primary target. However, it has been discovered that almost all the exposures taken in EPIC-pn fast Modes (Burst and Timing Mode) until the 23rd of May 2012 were unexpectedly affected by XRL. As of that date offset maps in these modes are being taken with the optical blocking filter in the CLOSED position, thus preventing source contamination.
As of SAS version 14.0, the reduction meta-tasks epproc and epchain run the XRL correction by default. Users are discouraged from interactively using epreject for this purpose.