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From: Adrian Turner <akt21@ast.cam.ac.uk>
Subject: Depression of local sensitivity in the OM
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Date: Tue, 10 Feb 2004 19:04:09 +0000
From: Adrian Turner <akt21@ast.cam.ac.uk>
To: xmmhelp <xmmhelp@xmm.vilspa.esa.es>
Subject: Depression of local sensitivity in the OM
Dear Helpdesk,

I was wondering was about a paragraph in the 'XMM-Newton Users' 
Handbook'. In section '3.5.2.1 Imaging with OM' there is a paragraph 
that states:


"In addition, sources which are too bright can depress the local 
sensitivity of the photocathode: this is a cumulative effect, so that 
fainter sources observed for long times have the same effect as brighter 
sources observed for shorter periods. This places some operational 
constraints on the instrument. Pointing of bright sources may also yield 
ghost images in subsequent observations due to fluorescence."


I was curious about this effect but could not find any documentation on 
it. Could you point out where these two effects are quantatively described?

Many thanks

Adrian Turner


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From: Matteo Guainazzi <xmmhelp@xmm.vilspa.esa.es>
To: akt21@ast.cam.ac.uk
Subject: Re: Depression of local sensitivity in the OM (PR#10149)
Date: Wed Feb 11 20:18:33 2004
Dear Adrian,

 The effect of loss of sensitivity and of remnant images after strong exposure
is
common to all intensified CCD's. There is no specific documentation related to
the
OM detector. However, you may find it described on general textbooks or
documentation, describing this type of instrumentation.

 The OM web pages at MSSL, where the instrument was built, contain a technical
overview of the instrument funtionalities, and of the physical principles on
which
it is based: http://mssls7.mssl.ucl.ac.uk/

 Regards,

 Matteo Guainazzi
 User Support Group
 XMM-Newton Science Operations Center

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