### LECS PSF

The LECS PSF is a strong function of energy and it is wider than that of MECS
below 1 keV while it is similar to that of MECS above 2 keV.

### MECS average PSF

In the following we give a brief decription of the MECS PSF
model and of its limits of applicability, for
a more detailed description see
Boella et al. 97 A&A in press.

The MECS PSF model currently available has been derived from on
axis measuraments and can be safely applied to
sources with off-axis angles < 4 arcmin. The model is
radially symmetric.

The MECS PSF is the convolution of 2 components: the
optics PSF and the detector PSF. For a sake of simplicity
it has been modeled as the sum of 2 components: a Gaussian
describing mainly the detector PSF and a King Profile
describing mainly the optics PSF. The parameters of
the two components and their relative normalizations
have first been derived at the 9 energies for which ground
calibration data was available; subsequently the
dependency of the above parameters on the Energy has been
fitted with algebraic functions. The final result is a
fully analytic differential PSF which can be analytically
integrated.

The ground derived PSF model has been tested
using the Cyg X-1 on-axis observation carried out in June
1996.

** Please send questions/problem reports to: helpdesk@sax.sdc.asi.it
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