[continues from 4.1.2]

4.1.3 Infinity correction

A further correction is necessary to reduce the measurements done at Panter at a finite source distance of 130 m (divergent beam) to the fligth condition of sources at infinity (parallel beam). The correcting coefficients have been derived by comparison of ground measurement with results of a ray tracing code. As such they are the same for all 3 MECS units.
The correcting factor is interpolated as a function of energy and off-axis angle theta from a set of coefficients kept in file panter.infinity.
The coefficients correspond to a cubic polynomial in theta.

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Fig. 4.1.3-I : examples of the Panter-to-infinity correction as a function of off-axis angle for three energies (1.5, 3.2 and 8.1 keV)

Additional representations (as separately numbered figures) can be obtained via the following form. inclusive of the overall vignetted area (compound calibration parameter, given by the product of the various corrections) :

Plot/compute ONE of the following parameters for MECS unit
Quantity vSymbolSelect
Infinity correction (unit-independent) I
Vignetting correction V (see section 4.1.2)
On-axis area A (see section 4.1.1)
Vignetted area (at finite distance) A*V
Positional correction V*I
Vignetted area at infinity A*V*I

select ONE type of data representation, the relevant parameter and data format
v(theta) at given E keV
v(E) at given theta arcmin
v(x,y) image at E keV

4.1.4 Focal length

The focal length of the mirrors is 1850 mm, which corresponds to a platescale (value read from provisional calibration file mir.dat) of 111.44 arcsec per mm in the focal plane.
The correspondence between mm and image pixels depends on the choice of the linearized pixel size during the linearization procedure. The unlinearized pixel sizes close to the detector centre are the average of the 3rd and 4th linearization coefficient in file m{1,2,3}_xy.coeff:

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