The HRI model is an analytic fit to the in-flight reponse, performed by MPE/GSFC/SAO. The functional form is,
where the radial distance R from the psf centre is in arcseconds. The constants A and S have values,PSF = A1*EXP(-0.5*(R/S1)**2) + A2*EXP(-0.5*(R/S2)**2) + A3*EXP(-R/S3)
This model provides a reasonable description of the psf out to radii of 100", but does not model the azimuthal asymmetry present within R12". The model will be updated when this effect can be parameterised.A1 = 0.9638 S1 = 2.1858" A2 = 0.1798 S2 = 4.0419" A3 = 0.001168 S3 = 31.69"
This model does not vary with position in the field of view.