4. The MECS calibration parameters

The Medium Energy Concentrator Spectrometer calibration parameters used by the XAS software reside in files in the $XASTOP/calib/sax/mecs directory, while those used by the SAXDAS software have been generated from the master XAS version.
We give here a reference to each calibration parameter, with indications of

4.0.1 Input photon energy grid

The input energy grid used in the computation of the response matrix can in principle be any grid of appropriate spacing. The current version of the MECS response matrix software uses an equispaced grid (hardcoded) of 1160 bins from 0.4 to 12 keV, each bin is 0.01 keV wide.

4.1 Mirror effective area

The effective area of the optics is given by the product of three components.

4.1.1 On-axis area

The on-axis area of the optics is tabulated as a function of energy in calibration files m{1,2,3}_onaxis.area
It has been calibrated on ground using various energies at the Panter calibration facility with the Mirror Units in the beam and without them (so called flat fields). The experimental results have been matched to the theoretical prediction (geometric area and gold reflectivity according to Henke 1983) by an ad-hoc second order polynomial.
A further adjustment (mainly around 2 keV) was made in flight using the Crab nebula spectrum.

The on-axis area (which corresponds to the Panter observing conditions, i.e. a point source at a finite distance of 130 m) is plotted here below.

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Fig. 4.1.1-I : MECS optics on-axis area


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