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pollin: Linearly dependent polarization

This multiplicative model applies a polarization with a linear dependence on energy. The factor applied depends on which Stokes parameter the spectrum is for. The Stokes parameter is determined using an XFLTnnnn keyword with values “Stokes:0”, “Stokes:1”, or “Stokes:2”, for I, Q, U, respectively.

The fraction and angle are determined by

$\displaystyle A(E) = {\tt A1} + (E-1.0) \times {\tt Aslope}$
$\displaystyle \psi(E) = {\tt psi1} + (E-1.0) \times {\tt psislope}$

The parameters are :

par1 A1, the polarization fraction at 1 keV
par2 Aslope, the polarization fraction slope
par3 psi1, the polarization angle at 1 keV (degrees)
par4 psislope, the polarization angle slope