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
- its physical meaning, and in which
hardware component it originates
- its current values
(inclusive of GIF plots : note that such plots are generated
on the fly and survive for 1 minute ; in case of problems RELOAD the HTML file
and RELOAD IMAGES as well)
- how it has been calibrated
- in which file(s) it resides
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.
The effective area of the optics
is given by the product of three components.
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.
Fig. 4.1.1-I : MECS optics on-axis area