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Method

There are two methods which may be used. Firstly, 'Calculation' mode, where the exposure time is calculated using the vignetting and wire corrections, essentially in the same way as in XRTCORR.

The corrections applied to the measured flux are :

  1. Divide by the over all exposure time
  2. Vignetting correct to the optical axis
  3. Apply a correction of 1.0/0.79 for absorption by the thin and thick wires in the PSPC support structure
The other method is to use the exposure map supplied with the observation; in this case exposure times near the ribs and central circle can be accurately calculated, however, the map is fixed over all times and all energies, so it will not be accurate if either the time axis or energy axis has been subset.


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