
Date: Wed, 8 Nov 2000 23:54:38 +0100 (MET)
From: Stefan Larsson <stefan@astro.su.se>
Subject: Re: Interactive background handling
To: smaisala@astro.helsinki.fi, njw@dsri.dk, allan@dsri.dk, peter.kretschmar@obs.unige.ch, luis@astro.su.se, eesko@astro.helsinki.fi, oxborrow@dsri.dk
Cc: stefan@des.astro.su.se
MIME-Version: 1.0
Content-MD5: tbdT9IxxvkKGZgo5h7EhKw==

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Interactive background handling for source extraction of 
lightcurves and spectra.
------------------------------------------------------------

In Standard Analysis the background subtraction is done
by correcting source count rates for the estimated net
background contribution based on the specified background model.
So no interaction, except that a different model can be specified.

A comment on NJW et al's e-mail.
The removal of sources is important both in this case and for
the calibrations we discussed at ISDC in September.
A tool could probably be based on either NJs simulation
software or on my photon tagging program.

Then a question to Sami. Can your software be used for fitting 
of alternative models to these source subtracted shadowgrams? 
I think it is important to be able to do at least one parameter 
fits and not just rely on visual comparisons.


The instrumental and the diffuse background components have quite
different spectra. If the instrument background varies across the 
detector the hardness ratio should do so too. It could therefore be
usefull to display a colour coded shadowgram of the hardness
ratio for two suitably selected energy bands. After background
subtraction there should be no such trend left. This should be
checked more quantitatively with a plot of the hardness ratio
from the center of the detector towards its edge.

Other posibilities:
- A user might like to select a set of background areas on
  sky images and build a background model from that.


Cheers,

Stefan

