SAS Watchout Page

Problems with epiclccorr - corrected with patched SASv8.0.1.

Two issues have been found during the a later validation stage of the new task epiclccorr, used for background subtraction and exposure correction of EPIC light curves:

• due to the use of a wrong keyword, the exposure correction for EPIC PN light curves does not take into account the time of reading out the detectors. This results in an underestimation of the count rates per bin, whose strength depends on the PN mode:
  
  
  • Timing: 1%
  • Extended Full Frame: 2%
  • Large Window: 5%
  • Full Frame: 6%
  • Small Window: 30%
  • Burst: 97%
  
  This does not affect MOS corrected light curves, but only the normalization of the corrected PN light curves.


• a bug in the handling of arrays corresponding to a source distributed over 2 or more CCDs, produces a segmentation fault when trying to correct a light curve obtained with such a multi-CCD selection area. This affects both EPIC MOS and PN.

Next sentence is obsolete after the patch 8.0.1. has been released on 27/10/2008. Please see the corresponding release notes.

Therefore, and until a patch for epiclccorr is available (we expect to release it in a couple of weeks), you should normalize the level of an epiclccorr PN corrected light curve yourself with the corresponding factor, as well as restrict selection for light curve extraction to areas corresponding to a single CCD.