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From: larkin.duelge@monash.edu
Subject: total exposure time
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Date: Wed, 6 Aug 2014 07:07:17 GMT
From: larkin.duelge@monash.edu
To: xmmhelp@sciops.esa.int
CC: larkin.duelge@monash.edu
Subject: total exposure time
Full_Name: Larkin
Submission from: (NULL) (122.107.138.247)


Sorry for this quick question that I can't seem to find any one to give me an
answer.  

For publication, if I stack many exposures (say 5) of 100ks each using all EPIC
cameras.is the stacked exposure time 5*100ks*3?

Thank you for your time
Larkin


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From: Jan-Uwe Ness <xmmhelp@sciops.esa.int>
To: larkin.duelge@monash.edu
Subject: Re: total exposure time (PR#74599)
Date: Wed Aug  6 08:16:26 2014
Dear Larkin,

 no, that is not correct. The stacked exposure time is 5*100ks (thus not three
times) - if you apply no filtering (see below). By combining the data from the
pn and MOS cameras you increase the effective area but not the exposure time. If
the effective areas where the same, this would be roughly equivalent but the
effective areas of pn is roughly twice that of each MOS camera. But there more
complex aspects to determine the effective area, and stacking can not be counted
in favor of the exposure time.

Before stacking the exposures, we recommend you check for time intervals of high
background which is described under:
http://xmm.esac.esa.int/sas/current/documentation/threads/EPIC_filterbackground.shtml
In many cases that reduces the exposure time to be quoted in a publication.

Hope this clarifies matters. Do not hesitate to ask if anything else is/remains
unclear.

 Best wishes,
Jan-Uwe


> Sorry for this quick question that I can't seem to find any one to give me
an
> answer.  
> 
> For publication, if I stack many exposures (say 5) of 100ks each using all
EPIC
> cameras.is the stacked exposure time 5*100ks*3?
> 
> Thank you for your time
> Larkin

--
   Dr. Jan-Uwe Ness
   XMM-Newton User Support Group
   European Space Astronomy Centre

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