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From: Stephen Drake <drake@olegacy.gsfc.nasa.gov>
Subject: EPIC Thick filter
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Date: Tue, 17 Sep 2002 12:32:04 -0400 (EDT)
From: Stephen Drake <drake@olegacy.gsfc.nasa.gov>
To: xmmhelp@xmm.vilspa.esa.es
cc: Steve Snowden <steve.snowden@gsfc.nasa.gov>
Subject: EPIC Thick filter
Hi:

   I had two observations of soft (about 0.2 KeV temperature for mekal
coronal plasma models), fairly faint (3 and 10 x 10-12 erg/s/cm2 in the
0.3- 3.0 keV energy range) targets with XMM, the second of which I have
just finished analyzing. The two targets (Beta Gem and Beta Hyi) are
both visually bright stars, and thus the EPIC Thick Filter was used in
both observations. Analyzing the data, I found that, in
both cases, the observed XMM EPIC PN & MOS fluxes were
3 - 10 times lower than previous ROSAT and Einstein fluxes (these sources
are too faint to get reliable RGS spectra). Since coronal
stars can vary, this may be a case of real intrinsic variability, although
it is rather unlikely in my opinion. I wanted to be able to rule out
the XMM calibration as the cause for this effect,and thus my question
is simply how accurately determined is the thick filter response?
Is there any possibility that its effective area is overestimated?
I noticed a comment in Marcus Kirsch's EPIC Calibration Status document
(XMM-SOC-CAL-TN-0018 on page 2) which states:
`Filter transmission of the MOS thick filter is currently not correctly
modelled and is under inverstigation'. This doesn't mention the PN thick
filter (as I mentioned above, I find consistent (low) fluxes for both
MOS1, MOS2,and the PN), I might note, implying that there is no known
problem with this combination.

    I would appreciate any advice you can give me on this point

                            Steve Drake

  PS The Obids of my 2 observations are 0006010401 and 0006010301

=========================================================================
    Dr. Stephen A. Drake,             
    Universities Space Research Association (USRA) Scientist,
    HEASARC/Code 662, Goddard Space Flight Ctr, Greenbelt, MD 20771, USA.
    Tel: 301 286 6962 or Fax: 301 286 1684.
=========================================================================
        
 


Reply 1

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From: Matthias Ehle <xmmhelp@xmm.vilspa.esa.es>
To: drake@olegacy.gsfc.nasa.gov
Subject: Re: EPIC Thick filter (PR#5921)
Date: Wed Sep 18 09:34:25 2002
Dear Steve Drake,

I have forwarded your question to the EPIC calibration scientist and will
let you know his reply as soon as possible.

Many thnaks for your report,

Matthias

Matthias Ehle 
XMM-Newton SOC 
User Support Group


Reply 2

Resend
From: Matthias Ehle <xmmhelp@xmm.vilspa.esa.es>
To: drake@olegacy.gsfc.nasa.gov
Subject: Re: EPIC Thick filter (PR#5921)
Date: Fri Apr 11 15:28:22 2003
Dear Steve Drake,

sorry for our late followup on your question - our calibration experts
now made the following comments:

you wrote:
>    I had two observations of soft (about 0.2 KeV temperature for mekal
> coronal plasma models), fairly faint (3 and 10 x 10-12 erg/s/cm2 in the
> 0.3- 3.0 keV energy range) targets with XMM, the second of which I have
> just finished analyzing. The two targets (Beta Gem and Beta Hyi) are
> both visually bright stars, and thus the EPIC Thick Filter was used in
> both observations. Analyzing the data, I found that, in
> both cases, the observed XMM EPIC PN & MOS fluxes were
> 3 - 10 times lower than previous ROSAT and Einstein fluxes (these sources
> are too faint to get reliable RGS spectra).

such a big change in flux can certainly not be explained by XMM-Newton
calibration uncertainties but must be due to a problem in the data
extraction used for the computation of the X-ray fluxes either for the
ROSAT and/or the EPIC data. 

Can you, please, make sure that you were using the correct spectral selection
expressions (for e.g. pattern, energies, source & backround areas). Info on
this
you can extract from our SAS Data analysis threads available at
http://xmm.vilspa.esa.es/external/xmm_sw_cal/sas_frame.shtml also explained 
at the end of the EPIC Calibration Status document linked at URL
http://xmm.vilspa.esa.es/external/xmm_sw_cal/calib/ ).

Cheers,
Matthias.

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