XMM-Newton Science Analysis System


omfchain (omfchain-1.43.2) [xmmsas_20230412_1735-21.0.0]

Flat-field

A flat-field file required by the Fast chain. It was originally envisaged that flat-filed images, generally obtained during spacecraft slews or periods when the OM is inactive, would be stored in an archive. This was intended, partly to monitor the evolution of the detector response and also to allow users to accumulate a statistically good flat-field from flats taken close in time to their observations. However, for a number of reasons this has so far proved unnecessary and a single OM flat-field is to be stored as a component of an OM Calibration File (OM_PIXTOPIXSENS). Due to the complexity of analysing the OM flat-field, at the current time the stored flat is a unit image (which is a reasonable approximation to $\approx 5\%$). This will be superceded by a `real' flat once better understanding of the flat-field variations and the gross response are attained. At present a warning will be issued noting that a template (i.e. a unit flat-field) is being used. This flat-field is created automatically within omfchain.