Viewing AO11/48816
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From: "Townsend L.J." <ljt203@soton.ac.uk>
To: "xmmhelp@sciops.esa.int" <xmmhelp@sciops.esa.int>
Date: Wed, 5 Oct 2011 17:23:50 +0100
Subject: PN short observation and pile-up

Hello,

I am trying to work out the best observing strategy for a source, but do not
fully understand the pile-up effects for bright sources. Is it true that the
shortest observation that can be made with XMM is 5ks and if so, why is this?
Initially the source will have a count rate in PN medium of ~30cts/s, which in
5ks is many more counts than I need, so am I unable to do a 1ks observation?
Secondly, pile up at this rate is, I'm sure, quite a problem. Can this be worked
around or should I be looking to perform such an observation in small window or
timing mode? To this end, is it possible with a sequence of observations, to
begin in small window mode and change to large window/full frame when the source
is much fainter?

Many thanks
Lee Townsend

Reply 1

From: Pedro M. Rodriguez Pascual <xmmhelp@sciops.esa.int>
To: ljt203@soton.ac.uk
Subject: Re: PN short observation and pile-up (PR#48816)
Date: Wed Oct  5 18:26:09 2011

Hello Lee,

The 5ks minimum observation duration has been defined as a compromise between
overheads and effective use of the science instrumnents: the setup of EPIC-pn
takes about 3ks, with slight differences among the modes, and the target
acquisition from previous pointing attitude typically takes about 6ks (on
average). 

About the pile-up, the small window mode should cope with 30cps without pileup
issues, but table 3 in the XMM-Newton UHB
(http://xmm.esac.esa.int/external/xmm_user_support/documentation/uhb/epicmode.html)
sets an upper limit of 50cps. Unfortunately, it is not possible to change the
instrument mode on the spot according to source brightness. In any case, the
source does not seem to be too bright for XMM-Newton and the details of the
instruments setup can be worked out later during the enhancement process.

Cheers,

Pedro