Corrects an EPIC-pn event list for spatial variations in the charge-transfer-inefficiency (CTI). This task should be run on the event file produced after all of the other CTI and gain corrections have been applied.
Measurements of the spectra of bright extended sources have shown that there is a pixel-to-pixel variation in the energy scale which is mainly caused by CTI changes due to partial trap saturation [1]. These can be represented, and corrected for, by a spatial CTI correction. For example the spatial varation in the measured energy of the O VII line (0.57 keV) from the VELA SNR can be seen in Fig. 1. After correction the response is much more uniform (Fig. 2).
It is currently recommended to apply this correction for observations taken in FullFrame and ExtendedFullFrame modes. There is some evidence that it may also procduce an improvement in LargeWindow and SmallWindow modes, however, it should not be applied for Timing mode or Burst mode observations.
To avoid the corrections being applied twice, a keyword SPATCTIC is set in the header of the EVENTS extension when the task terminates successfully.
