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From: pae@astro.keele.ac.uk
Subject: EPIC-PN background issue
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Date: Mon, 20 Sep 2004 10:52:05 GMT
From: pae@astro.keele.ac.uk
To: xmmhelp@xmm.vilspa.esa.es
CC: pae@astro.keele.ac.uk
Subject: EPIC-PN background issue
Full_Name: 
Submission from: (NULL) (160.5.87.25)


I am analysing observation ID 0144840101, an observation of HT Cam (Pn in Full
Frame mode). The MOS data is fine. In the PN data, the source count rate drops
sharply around 11.3 keV (presumably a detector edge), but the background count
rate doesn't show this feature until ~15.5 keV. There is also a prominant line
in the background spectrum, presumably the 6.4-keV Iron line (which is the only
noteable line in the source), but it is cenred around 8 keV instead. I can
provide a .ps figure showing these 2 spectra, if required. The background area
in question is the entirity of CCD4, excluding the area contaminated by source
counts, and the strip running down the CCD. The source area is a circle centred
on the source (pile-up is not an issue). The rmf and arf were generated using
the relevant xmmsas tasks (xmmsas v6).

Do you know why there appears to be an energy offset between the source and
background spectra? Is there anything I can do about it?

Thanks

Phil


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From: Maria Santos-Lleo <xmmhelp@xmm.vilspa.esa.es>
To: pae@astro.keele.ac.uk
Subject: Re: EPIC-PN background issue (PR#16232)
Date: Mon Sep 20 16:47:09 2004
Dear Phil, 

> I am analysing observation ID 0144840101, an observation of HT Cam (Pn in
Full
> Frame mode). The MOS data is fine. In the PN data, the source count rate
drops
> sharply around 11.3 keV (presumably a detector edge), but the background
count
> rate doesn't show this feature until ~15.5 keV. 

The PN effective area for X-ray photons drops sharply beyond ~10 keV. 
The EPIC background is complicated and includes different components, 
some are due to photons and other to particules -like solar soft protons. 
Some of these background components are highly variable, in particular the
solar protons vary and can be the dominant contribution. Given the 
difference in origin, in principle, it is not surprising that the background 
count rate does not drop sharply at the same time as the source count rate
does. If you need more details about XMM EPIC background, you can read
the following paper: Read & Ponman, (2003, A&A, 409, 395) or 
astro-ph 0304147

> There is also a prominant line
> in the background spectrum, presumably the 6.4-keV Iron line (which is the
only
> noteable line in the source), but it is cenred around 8 keV instead. I can
> provide a .ps figure showing these 2 spectra, if required. The background
area
> in question is the entirity of CCD4, excluding the area contaminated by
source
> counts, and the strip running down the CCD. The source area is a circle
centred
> on the source (pile-up is not an issue). The rmf and arf were generated
using
> the relevant xmmsas tasks (xmmsas v6).
> 

The background spectrum of the pn camera has some features due to 
fluorescence from the detector and the structure surrounding it. In 
particular, there is a feature around 8 keV due to Ni, Cu and Zn K-alpha 
lines. You can see more details in the XMM-Newton User's Handbook at 

http://xmm.vilspa.esa.es/external/xmm_user_support/documentation/uhb/node35.html

Hope this solves your problem , but if it is not the case, do not hesitate 
to let us know.

Best regards

Maria

Maria Santos-Lleo, 
XMM-Newton SOC 
User Support Group

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