Method

The program corrects for the following effects with the following assumed dependencies:

   Correction        Pos. dependent     Energy dept.    Time dept.
  ------------      ----------------   --------------  ------------
   DEAD TIME              NO                NO             YES
   WIRES                  NO                NO             NO
   VIGNETTING             YES               YES            NO
   POINT SPREAD           YES               YES            NO
   BORON FILTER           NO                YES            NO

Time series:

A time series will be corrected for all the above effects. For the energy dependent corrections a mean photon energy of 0.2 keV will be assumed. This may be overridden on the command line by e.g.

  ICL> XRTCORR ENERGY=0.4

The final data array is normalised by dividing by the exposure time.

Images

Images are corrected for dead time and vignetting. The final data array is normalised by the exposure time. The vignetting correction is only an approximation to allow subsequent image processing work to be performed. It works be calculating the vignetting at each pixel at a default energy of 0.2 kev (changed by specifying ENERGY=nn on the comand line).

Spectra

Spectra are treated differently. The data are corrected for the energy independent factors and then normalised by the exposure time. Energy dependent factors are combined and written into an extension within the instrument box of the datafile,

       MORE.ASTERIX.INSTRUMENT.ENCORR(1).DATA_ARRAY

This array containing correction factors for 729 energies is used by the detector response program XRTRESP to modify the detector matrix so that it is appropriate for the particular datafile being used. NB: RADIAL_SPECTRA contain one such array for each radial bin.

Spectral images:

These are corrected for dead time and vignetting. The vignetting is performed separately for each spectral bin by calculating the approximate mean energy of the bin and then using the effective area curve relevant to this energy. Note this is an appoximation only ! Files which have been corrected like this cannot be used for spectral fitting! This option is an image analysis tool only.

• RADIAL BINS
• Dead time
• Wires
• Effective Area & Vignettin
• Point spread