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XMM-Newton Science Analysis System


lccorr (lccorr-2.27.1) [xmmsas_20060628_1801-7.0.0]

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1. The correction for pixels masked by cosmic rays can only be approximate because some events are rejected as cosmic rays onboard the spacecraft. Full spatial information is not returned, but the number of pixels involved per frame is calculated and stored in the EXPOSUnn extensions of the calibrated event list product. At present lccorr bin-averages these numbers to the same bin times and size as the TS and includes them on this basis in the calculation of FRACEXP. Several alternative schemes are possible:

   Scheme	Advantages	Disadvantages
   Ignore	No added noise	Wrong total flux
   	Simplest scheme	No provision for slow drift in CR intensity
   Bin to same fineness as TS	Correct total flux	Added noise
   	Correct for slow drift in CR intensity
   Average over whole TS	Correct total flux	No provision for slow drift in CR intensity
   	No added noise
   Bin somewhat coarser than TS	Optimized correction	Most complex scheme

   The last scheme may be adopted in a future version of lccorr, or the choice of scheme may be made selectable by parameter.

2. No account is taken as yet of significant variations in spacecraft pointing or attitude. It is assumed that events occurring during unacceptably large attitude excursions have been rejected via GTIs set further `upstream'.