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From: nathansecrest@msn.com
Subject: Correcting for Source Overlap
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Date: Wed, 23 Apr 2014 20:28:42 GMT
From: nathansecrest@msn.com
To: xmmhelp@sciops.esa.int
CC: nathansecrest@msn.com
Subject: Correcting for Source Overlap
Full_Name: Nathan Secrest
Submission from: (NULL) (69.140.37.211)


Hello, I'm presently working on an XMM dataset of pn and mos data.  My main
source is somewhat close to a second source (~21"), and so I am trying to figure
out the best way of estimating the contamination of my source by the second, as
well as determining an aperture-corrected flux.

My best idea for doing this is to extract the events of my source using the
half-energy radius of pn on the pn data and the half energy radius of mos on the
mos data, then compare the two (since they should give the same flux level for
the same point source), and determine the excess in the pn data, since the pn
PSF has a larger half energy radius.  But it seems to me that the mos data will
still have some residual contamination, so this is an imperfect method.

Is there a known method for determining the flux from just one source when it is
relatively close to another?

Thanks,

Nathan Secrest


Reply 1

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From: Pedro M. Rodriguez Pascual <xmmhelp@sciops.esa.int>
To: nathansecrest@msn.com
Subject: Re: Correcting for Source Overlap (PR#74052)
Date: Thu Apr 24 16:49:42 2014
Hi,

arfgen is able to compute the effective area within a given extraction region
coming from a source located somewhere else.  Assume source 1 is located in
X1,Y1 and source 2 in X2,Y2, both being point-like sources ; let spec1.fits be
the spectrum extracted within a circle of radius R1 and centered at X1,Y1

1) arfgen spectrumset=spec1.fits arfset=arf1.fits rmfset=rmf.fits
withrmfset=yes

arf1.fits will be the effective for source1 within circle X1,Y1,R1

2) arfgen spectrumset=spec1.fits arfset=arf21.fits rmfset=rmf.fits
withrmfset=yes  withsourcepos=yes sourcex=X1 sourcey=Y2 sourcecoords=pos

arf21.fits will be the effective for source2 within the circle X1,Y1,R1

Then, if S1 is the photon spectrum of source1 and S2 is the photon spectrum of
source2, the count spectrum (C1) within circle X1,Y1,R1 (i.e. spec1.fits) will
be

C1 = S1*A1 + S2*A21

where A1 is the effective area for source1 within circle X1,Y1,R1 (i.e.,
arf1.fits) and A21 the effective area of source2 within circle X1,Y1,R1 (i.e.
arf21.fits)

All these files can loaded in xspec as:

data spec1.fits
resp 1:1 rmf.fits
arf 1:1 arf1.fits
resp 2:1 rmf.fits
arf 2:1 arf21.fits

... and the different models for the different sources

model 1:s1 phabs*power
model 2:s2 phabs*mekal

Cheers,

Pedro

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