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From: pu@astro.soton.ac.uk
Subject: EPICpn live time
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Date: Tue, 27 May 2003 14:16:44 GMT
From: pu@astro.soton.ac.uk
To: xmmhelp@xmm.vilspa.esa.es
CC: pu@astro.soton.ac.uk
Subject: EPICpn live time
Full_Name: Phil Uttley
Submission from: (NULL) (152.78.0.28)


Hello,
I am analysing an EPIC-pn large window mode observation. The LIVETIME value in
the
event file is only 93.6% of the ONTIME.  This fraction matches the corrected
exposure
in the spectrum extracted from the file, once the telemtry dropouts have been
taken out
of the original exposure time.  I am puzzled as to why the livetime is 93.6%
instead
of the 94.9% (and 0.16% OOT fraction) which is quoted in the users handbook.
Does the actual livetime change between observations?  It is important that I
get the
correct livetime, since I need to correct count rates in a light curve so I can
compare pn light curves obtained in two different modes. 
   Thanks,
        Phil Uttley


Reply 1

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From: Matthias Ehle <xmmhelp@xmm.vilspa.esa.es>
To: pu@astro.soton.ac.uk
Subject: Re: EPICpn live time (PR#8586)
Date: Tue May 27 15:06:22 2003
Dear Phil Uttley,

I have forwarded your question to the pn experts and will let you know
their answer as soon as possible.

Cheers,
Matthias.

Matthias Ehle 
XMM-Newton SOC 
User Support Group


Reply 2

Resend
From: Matthias Ehle <xmmhelp@xmm.vilspa.esa.es>
To: pu@astro.soton.ac.uk
Subject: Re: EPICpn live time (PR#8586)
Date: Mon Jun 30 11:23:27 2003
Dear Phil Uttley,

sorry for my late reply - please, find attached now the answer received from
th pn expert:

The number quoted in the users' handbook seems to be ok, also
in the Technical Note by M. Kuster and B. Kretschmar (Sept. 2002) a life 
time of 94.86% is stated.

This life time is defined by the readout sequence in large window mode,
which is always constant, so there is no "observational dependent" life time.

On the other hand, any other losses caused by counting mode or telemetry
outages are different from observation to observation and have to be
taken into account for the generation of light curves.

Cheers,
Matthias.

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