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From: cocj@roe.ac.uk
Subject: More PSF confusion
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4 replies: 1 2 3 4
6 followups: 1 2 3 4 5 6

Private message: yes  no

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Date: Wed, 17 Mar 2004 16:28:31 GMT
From: cocj@roe.ac.uk
To: xmmhelp@xmm.vilspa.esa.es
CC: cocj@roe.ac.uk
Subject: More PSF confusion
Full_Name: Olivia Johnson
Submission from: (NULL) (195.194.120.192)


Hi, 

  I'm trying to find the dependence of the encircled energy on off-axis angle,
so that I can apply appropriate circular apertures for a stacking analysis.  I
have tried using CalView to make .fits images of the PSF at various OAA (medium
accuracy model), and find that, strangely, the 80% EE radius is only very 
weakly dependent on OAA at 2 keV, and actually dips from OAA=0 to OAA=7 or so.

  I assumed I had done something wrong, and so consulted the helpdesk archive
on
PSF problems, where I read the following in response to message
Calibration/7320,
in which a user has used the King profile parameters to work out EE and is 
surprised by the lack of variation with OAA:
>Your calculations are correct. There appears to be surprisingly little
>change in the encircled energy fraction as you move off axis for all
>of the cameras. Although the shape does distort and elongate beyong ~7
>arcmins, the encircled fraction stays roughly constant. I also found a plot 
in version 1.1 of the User's handbook which is still on-line at
http://www.mssl.ucl.ac.uk/www_xmm/ukos/onlines/uhb/XMM_UHB/XMM_UHB.html
which seemed to exactly reproduce my results from CalView, with very little
variation with OAA and a dip at moderate OAAs.
  
  Just when I'd begun to think this was the true behavior of the EE with OAA 
despite the apparently obvious expansion of the PSF at large OAAs, I looked 
to the most recent version of the UHB (off the vilspa page) to see if 
anything was said about the physical reason behind this curious behavior.  
There I saw completely different plots of 90% EE vs. OAA, this time with 
significant increases in the radius as I had originally expected.  

  Would you please explain the discrepancies, and let me know I could obtain
the
data used to plot Figures 9 & 10 of version 2.1 of the User's handbook. 

Thanks, 
-Olivia Johnson


Reply 1

Resend
From: Nora Loiseau <xmmhelp@xmm.vilspa.esa.es>
To: cocj@roe.ac.uk
Subject: Re: More PSF confusion (PR#10394)
Date: Thu Mar 18 13:38:19 2004
Dear Olivia,

I forwarded your question to our experts. I will come back to you as
soon as they provide me an explanation.

Best regards,

Nora
..........----
Dr. Nora Loiseau
XMM-Newton User Support Group


Reply 2

Resend
From: Nora Loiseau <xmmhelp@xmm.vilspa.esa.es>
To: cocj@roe.ac.uk
Subject: Re: More PSF confusion (PR#10394)
Date: Mon Mar 22 11:22:39 2004
Dear Olivia,

here is the reply to your question from our SAS expert.

Best regards,

Nora

------------------------------

  the user has looked at the Medium mode PSF with calview.
This is the old, now superseded method of calculating the encircled
energy, which agrees with the plots in the UHB version 1.1.

Using the EXTENDED PSF mode (King model), which is the current recommended
method, the encircled energy has a different dependence on off-axis-angle from
the medium mode although this dependence is still small.
Figures 9 and 10 in Version 2.1 of the UHB are I think out of date.
We are now updating them for next version.

Anyway, the bottom line is that from in-orbit measurements the encircled energy
seems to be a slow function of off-axis angle for all the Epic cameras.
----
Dr. Nora Loiseau
XMM-Newton User Support Group


Followup 1

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Date: Tue, 23 Mar 2004 12:19:32 +0000 (GMT)
From: Olivia Johnson <cocj@roe.ac.uk>
To: Nora Loiseau <xmmhelp@xmm.vilspa.esa.es>
Subject: Re: More PSF confusion (PR#10394)
Dear Nora,

Thanks for the quick reply.  Is there a plot and/or data currently
available that represent the appropriate behavior of encircled energy with
off-axis angle?  This is a basic instrument characteristic and should not
have to be rederived by each user, and the many versions of calibration
data and documentation available make this quite confusing for a novice.
I need only a rough indication of radius for a given encircled energy at
e.g. 2 arcminute off-axis intervals across the field of view.

Thanks,
Olivia


On Mon, 22 Mar 2004, Nora Loiseau wrote:

> Dear Olivia,
>
> here is the reply to your question from our SAS expert.
>
> Best regards,
>
> Nora
>
> ------------------------------
>
>   the user has looked at the Medium mode PSF with calview.
> This is the old, now superseded method of calculating the encircled
> energy, which agrees with the plots in the UHB version 1.1.
>
> Using the EXTENDED PSF mode (King model), which is the current recommended
> method, the encircled energy has a different dependence on off-axis-angle
from
> the medium mode although this dependence is still small.
> Figures 9 and 10 in Version 2.1 of the UHB are I think out of date.
> We are now updating them for next version.
>
> Anyway, the bottom line is that from in-orbit measurements the encircled
energy
> seems to be a slow function of off-axis angle for all the Epic cameras.
> ----
> Dr. Nora Loiseau
> XMM-Newton User Support Group
>



Followup 2

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Date: Tue, 23 Mar 2004 14:36:41 +0000 (GMT)
From: Olivia Johnson <cocj@roe.ac.uk>
To: Nora Loiseau <xmmhelp@xmm.vilspa.esa.es>
Subject: Re: More PSF confusion (PR#10394)
Hi Nora,

  One last follow-up on my last message.  I have downloaded fits files
from the extended accuracy model for both pn and MOS and performed the
same encircled energy analysis I conducted on the medium accuracy model.
Indeed, I now see a range in 80% encircled energy from on-axis source to
those at 14' off-axis of 43.75 - 44.0 pixels for pn and 43.98 - 43.99
pixels for MOS, if the PSF is normalized at about 1'.  The encircled
energy curves for each off-axis position (so percentage of flux within
a 50 pixel radius vs. radius in pixels) look virtually identical.  I
realize the sources have been radially averaged, but simply looking at the
banana shape of the PSF at large off-axis angles it seems this can't be
right - there must be variation in the radial distribution of light
between on-axis and off-axis sources musn't there?  Normalizing the PSF
at just over 2', the maximum allowed by the calview images, gives a much
larger 80% EE value (~80 pixels) which decreases with OAA in both
instruments.

Cheers,
-olivia




Followup 3

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Date: Tue, 23 Mar 2004 16:10:35 +0000 (GMT)
From: Olivia Johnson <cocj@roe.ac.uk>
To: Nora Loiseau <xmmhelp@xmm.vilspa.esa.es>
Subject: Re: More PSF confusion (PR#10394)
Hi again Nora,

  Apologies, one more update.  Please disregard my last email - I did not
realize the image size was altered in the extended accuracy model and
there was therefore a bug in my code.  I have corrected this, and now for
pn I see an 80% EE value for the pn of just under 25 pixels and for the
MOS of about 21 pixels, both increasing slightly with off axis-angle. The
50%EE value is practically constant for MOS at just over 8 pixels, and is
10 pixels on-axis _decreasing_ to 8 for the pn.  This behavior still seems
strange to me.  Could you confirm that this is correct and also that the
pixel size for the extended accuracy model PSF images is still 1.1"

Thanks, and sorry for the mix-up.

-Olivia





Followup 4

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Date: Wed, 24 Mar 2004 10:28:08 +0000
From: Nora Loiseau <nloiseau@xmm.vilspa.esa.es>
To: cocj@roe.ac.uk
CC: xmmhelp@xmm.vilspa.esa.es
Subject: Re: More PSF confusion (PR#10394)
This is a multi-part message in MIME format.
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Dear Olivia,

Please find attached the 90% enclosed energy plot for MOS-1, which is 
different from that presented in the current UHB. The PN plot 
in the UHB still represents current knowledge.

There are many combinations of photon energy, off-axis angle, instrument
and encircled energy which could be plotted. We can not provide all
of these. The user can derive the specific plots that they want using 
calview.
In this case the general recipe is:

1. Create a cif with cifbuild and make sure that it contains the files
XRT1_XPSF_0006.CCF, XRT2_XPSF_0006.CCF, XRT3_XPSF_0005.CCF

2. run calview

3. Select the required instrument
select "Accuracy Level" = EXTENDED
set "Energy (eV)" to required photon energy
set Theta to 0 arcseconds

4. View->Encircled_energy->Encircled_energy(PSF)

5. Read from the resulting plot the radius which contains the required 
encircled energy fraction.

6. Set Theta to 120 arcseconds and then repeat etc....

We are sorry for the out of date documentation on the PSF,
our experts are working hard to bring it up to date.

Regards,

Nora







-- 
--
Dr. Nora Loiseau,
XMM-Newton User Support Group       phone: +34 918131298
nloiseau@xmm.vilspa.esa.es          FAX:   +34 918131322


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Followup 5

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Date: Thu, 1 Apr 2004 19:05:46 +0100 (BST)
From: Olivia Johnson <cocj@roe.ac.uk>
To: Nora Loiseau <nloiseau@xmm.vilspa.esa.es>
Cc: xmmhelp@xmm.vilspa.esa.es
Subject: Re: More PSF confusion (PR#10394)
Hi again Nora,

  One last related question: Does the SAS detect chain (eboxdetect ->
emldetect) use the EXTENDED or the MEDIUM accuracy model to correct the
source and background counts?  I'm noticing the fluxes I get from
aperture photometry (corrected using the EXTENDED model) are
significantly lower than those I get from the SAS detect chain, and wonder
if this could be why.

Cheers,
-Olivia


On Wed, 24 Mar 2004, Nora Loiseau wrote:

> Dear Olivia,
>
> Please find attached the 90% enclosed energy plot for MOS-1, which is
> different from that presented in the current UHB. The PN plot
> in the UHB still represents current knowledge.
>
> There are many combinations of photon energy, off-axis angle, instrument
> and encircled energy which could be plotted. We can not provide all
> of these. The user can derive the specific plots that they want using
> calview.
> In this case the general recipe is:
>
> 1. Create a cif with cifbuild and make sure that it contains the files
> XRT1_XPSF_0006.CCF, XRT2_XPSF_0006.CCF, XRT3_XPSF_0005.CCF
>
> 2. run calview
>
> 3. Select the required instrument
> select "Accuracy Level" = EXTENDED
> set "Energy (eV)" to required photon energy
> set Theta to 0 arcseconds
>
> 4. View->Encircled_energy->Encircled_energy(PSF)
>
> 5. Read from the resulting plot the radius which contains the required
> encircled energy fraction.
>
> 6. Set Theta to 120 arcseconds and then repeat etc....
>
> We are sorry for the out of date documentation on the PSF,
> our experts are working hard to bring it up to date.
>
> Regards,
>
> Nora
>
>
>
>
>
>
>
> --
> --
> Dr. Nora Loiseau,
> XMM-Newton User Support Group       phone: +34 918131298
> nloiseau@xmm.vilspa.esa.es          FAX:   +34 918131322
>
>



Reply 3

Resend
From: Nora Loiseau <xmmhelp@xmm.vilspa.esa.es>
To: cocj@roe.ac.uk
Subject: Re: More PSF confusion (PR#10394)
Date: Fri Apr  2 10:49:17 2004
Deal Olivia,

medium accuracy model is used. Can you specify which method did you use for
aperture photometry, and give us as many details as possible?.

Cheers,

Nora


>   One last related question: Does the SAS detect chain (eboxdetect ->
> emldetect) use the EXTENDED or the MEDIUM accuracy model to correct the
> source and background counts?  I'm noticing the fluxes I get from
> aperture photometry (corrected using the EXTENDED model) are
> significantly lower than those I get from the SAS detect chain, and wonder
> if this could be why.
----
Dr. Nora Loiseau
XMM-Newton User Support Group


Followup 6

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Date: Fri, 2 Apr 2004 12:43:19 +0100 (BST)
From: Olivia Johnson <cocj@roe.ac.uk>
To: Nora Loiseau <xmmhelp@xmm.vilspa.esa.es>
Subject: Re: More PSF confusion (PR#10394)
Hi Nora,

 Thanks for the quick reply.  Here's what I'm doing:

  I've run a variant of the CIAO wavdetect algorithm on the image which
produces a smooth source-free image of the background, and a sourcelist
which includes an estimate of source extent in pixels.  Then:

ap_counts = counts in a 2*4.35 pixel aperture from the counts image
ap_bkg =    counts   "   "   "   "   "   "    from the background image
ap_expo =   counts   "   "   "   "   "   "    from the exposure image

  I find the encircled energy in my aperture by interpolating the curve
from the extended accuracy model, ee.  Then:

tot_counts = ap_counts/ee

tot_background = ap_bkg * npix_source / npix_aperture  where n_pix source
						       is from the WD cell

net_counts=tot_counts - tot_background

exposure = ap_expo / n_pix aperture

flux=counts/exposure/ecf

  I've attached a plot of my counts vs. the detect chain counts for the
three detectors in one band.  As you can see, I'm systematically low, and
the SAS counts flatten out at low fluxes.

  I've checked that the WD background map is comparable to the splinefit
one - it's alot smoother, but the level is consistent to counts
equivalent to ~10^16 erg/s/cm^2.

  I've also just checked the discrepancy for the ee fraction between
MEDIUM and EXTENDED accuracy modesl (I only checked for MOS), but this
effects the net_counts at only at the 3-7% level for my aperture size.

  I imagine the trouble must be in the estimate of source size used to
normalize the background counts.  The WD algorithm defines source cells in
a PSF-indepedent way, and perhaps this is larger than the assumed 100%EE
radius for the SAS background count calculation?  Any suggestions you have
on this would be much appreciated.

Thanks,
-olivia


On Fri, 2 Apr 2004, Nora Loiseau wrote:

> Deal Olivia,
>
> medium accuracy model is used. Can you specify which method did you use for
> aperture photometry, and give us as many details as possible?.
>
> Cheers,
>
> Nora
>
>
> >   One last related question: Does the SAS detect chain (eboxdetect
->
> > emldetect) use the EXTENDED or the MEDIUM accuracy model to correct
the
> > source and background counts?  I'm noticing the fluxes I get from
> > aperture photometry (corrected using the EXTENDED model) are
> > significantly lower than those I get from the SAS detect chain, and
wonder
> > if this could be why.
> ----
> Dr. Nora Loiseau
> XMM-Newton User Support Group
>



Reply 4

Resend
From: Nora Loiseau <xmmhelp@xmm.vilspa.esa.es>
To: cocj@roe.ac.uk
Subject: Re: More PSF confusion (PR#10394)
Date: Fri Apr  2 13:40:50 2004
Dear Olivia,

this seems to be data analysis problem, not really a problem of SAS,
and unhappily we do not have enough manpower for helping in that.

Best regards,

Nora
----
Dr. Nora Loiseau
XMM-Newton User Support Group

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