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From: fenghua01@mails.tsinghua.edu.cn
Subject: King Parameters of PSF
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Date: Fri, 20 Sep 2002 02:46:53 GMT
From: fenghua01@mails.tsinghua.edu.cn
To: xmmhelp@xmm.vilspa.esa.es
CC: fenghua01@mails.tsinghua.edu.cn
Subject: King Parameters of PSF
Full_Name: Hua Feng
Submission from: (NULL) (218.2.131.246)


The XMM EPIC PSF can be fitted by a King function. And the 
King function parameters are listed in the last CCF files.
From the King function, the PSF and FWHM can be presented as:
    PSF = 1/(1 + (r/rc)^2)^a            (1)
    FWHM = 2*rc*sqrt(2^(1/a) - 1)       (2)
where rc is the core radius of the King function and a is the King slope.
So I can figure out FWHMs form the King parameters and they are listed below:
EMOS1(XRT1_XPSF_0005.CCF) with field angle = 0
    energy(ev)     rc(arcsec)       a      fwhm(arcsec)
            0        5.074        1.472       7.8699
          100        5.050        1.471       7.8366
         1500        4.720        1.457       7.3680
         3000        4.366        1.442       6.8599
         4500        4.012        1.427       6.3454
         6000        3.658        1.412       5.8243
         7500        3.304        1.397       5.2964
        10000        2.714        1.372       4.4008
        12000        2.242        1.352       3.6697
        13500        1.888        1.337       3.1124

From this table, we can see it does not consist with the FWHMs
anounced in the User's Hand Book. It seems a little larger in low energy
and a little smaller in high energy. There are the same situations for 
EMOS2 and EPN. I know that these parameters are fitted from experimental 
data with such equations: 
    rc = a + b*E + c*theta + d*E*theta       (3)
     a = x + y*E + z*theta + w*E*theta        (4)
Also I ploted the image in the CCF PSF file and calculated the
FWHM from interpolation. They are different much with the analytic ones
above and do not differ so much between high and low energy. These differences 
will take effect to my work.

Are the fitted King parameters reliable? In which way can I get a most
accurate PSF?

Best regards,
Hua Feng


Reply 1

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From: Matthias Ehle <xmmhelp@xmm.vilspa.esa.es>
To: fenghua01@mails.tsinghua.edu.cn
Subject: Re: King Parameters of PSF (PR#5944)
Date: Fri Sep 20 10:33:17 2002
Dear Hua Feng

I have contacted our PSF experts about your questions and will let you
know their reply.

Cheers,
Matthias.

Matthias Ehle 
XMM-Newton SOC 
User Support Group


Reply 2

Resend
From: Matthias Ehle <xmmhelp@xmm.vilspa.esa.es>
To: fenghua01@mails.tsinghua.edu.cn
Subject: Re: King Parameters of PSF (PR#5944)
Date: Tue Sep 24 09:05:47 2002
Dear Hua Feng

the PSF experts provided me now with the following answers to your PSF
questions:

> Are the fitted King parameters reliable? In which way can I get a most
> accurate PSF?

The estimation of the best fit parameters have been worked out using a large 
set of data. Man (or rather Woman) years have been spent on this and we are 
confident that the King profile parameterisations are accurate and represent 
the best currently available 1-d PSF. 

The areas of uncertainty, namely high energies at large off-axis angles are 
described in the in the XMM-SOC-CAL-TN-0022 document.

It was found indeed that the FWHM is smaller than expected for high energies
and a little larger than expected for low energies. The FWHM values reported 
in Table 2 of the Users' Handbook are based on earlier measurement and should 
be updated. We think that the values out of the King parametrization can be
used.

> Also I ploted the image in the CCF PSF file and calculated the
> FWHM from interpolation. They are different much with the analytic ones
> above and do not differ so much between high and low energy.

The 2-D images are described to some extent in the Calibration Access and
Data Handbook (available from http://xmm.vilspa.esa.es/ccf/documents/
as well) and CCF release notes (XRT1/2/3_PXSF). However, there are known 
problems with these CCF data and a 2-d mapping of the PSF with in-orbit data 
is an outstanding calibration issue.

Best regards,
Matthias.

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