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Comments XMM-Newton SAS Home Page
XMM-Newton Science Analysis System


lccorr (lccorr-2.27.1) [xmmsas_20060628_1801-7.0.0]

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Comments

  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'.


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XMM-Newton SOC/SSC -- 2006-06-28