[continues from 4.11]

4.11.1 The PSF of the Mirror Units

The PSF of the optics alone was also calibrated on the ground [4] and is well described as a sum of four Lorentzians (i=1,4) of the form :
       Li(r) = Gi(E) / { pi Bi(E)2 [1+(r/Bi(E))2]2  }
The relevant coefficients Gi and Bi depend on energy (via a rough linear interpolation), are the same for all MECS units, and are kept (expressed for r in mm) in calibration file psf_mir.dat.

The coefficients are used exclusively to compute the transmission of the Be window as a function of position, since the strongback is illuminated by a beam broadened by the optics PSF only. Please do not be misled, for any other purpose the optics+detector PSF is used.

Additional figures can be produced using the following form :

kind of representationparameterform
B and G coefficients vs energy none
Differential PSF(E,r) vs r at fixed energy E keV
Integral PSF(E,r) vs r at fixed energy E
(aka Encircled Energy Function)

4.11.2 The PSF of Detector

The PSF of the detector alone has a gaussian shape and can be measured on the ground without the optics, either directly using pin-holes, or indirectly using flat field illumination (e.g. from the shape of the detector window borders). However since it does not enter directly any flight relevant parameter, there are no calibration files associated with it.

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