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From: mariano@astro.rug.nl
Subject: Systematic uncertainties MOS/PN (e.g. in Xspec)
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Date: Fri, 1 Aug 2008 11:15:10 GMT
From: mariano@astro.rug.nl
To: xmmhelp@sciops.esa.int
Cc: mariano@astro.rug.nl
Subject: Systematic uncertainties MOS/PN (e.g. in Xspec)
Full_Name: Mariano Mendez
Submission from: (NULL) (129.125.6.1)


Hi:

I searched the XMM-Newton site but could not find this: Do you recommend a
systematic uncertainty for PN and MOS to be added in quadrature to the
statistical errros to account for calibration uncertainties? (This, besides the
fact that different instruments may give different fluxes, which is usually
taken care of by having a multiplicative constant in the model when one fits
several instruments simultaneously.)

I read the latest calibration report, and I thought the number could be ~5%, but
perhaps not for the whole energy range. 

From simultaneous fits with PN and MOS (allowing for a multiplicative constant
as I mentioned above), I see that below ~2 keV there is a difference between MOS
and PN that goes from ~ 10% at 0.6 keV to 1-2 % at 2 keV. Above that energy, the
residuals overlap quite okay.

It would be good if this is included in the thread explaining how to fit EPIC
data in Xspec. It would be reasuring for the users to have it somewhere from an
"official source", so to speak.

Thanks,

Mariano.


Reply 1

Resend
From: Nora Loiseau <xmmhelp@sciops.esa.int>
To: mariano@astro.rug.nl
Subject: Re: Systematic uncertainties MOS/PN (e.g. in Xspec) (PR#37460)
Date: Fri Aug  1 13:31:23 2008
Dear Mariano,

I just forwarded your questions to the EPIC calibration scientists. I 
will come back to you as soon as I get their reply.

Best regards,

Nora
----
Dr. Nora Loiseau
XMM-Newton User Support Group


Reply 2

Resend
From: Nora Loiseau <xmmhelp@sciops.esa.int>
To: mariano@astro.rug.nl
Subject: Re: Systematic uncertainties MOS/PN (e.g. in Xspec) (PR#37460)
Date: Tue Aug  5 09:00:34 2008
Hi Mariano,

here is the reply by the calibration scientist:
===
the best answer we can provide is: "please look at the cross-calibration
archive" (http://xmm2.esac.esa.int/cgi-bin/ept/preview.pl). Especially the
sections on the statistical evaluation of fluxes have been designed for a user
to make her/his own evaluation on our level of understanding of the
cross-calibration status. Additionally, there is no strong evidence for an
average difference in spectral shape between MOS and pn in the soft energy band,
if data are reduced with SASv7.1 with a CCF generated after August 2007
===

Best regards,

Nora

> Hi:
> 
> I searched the XMM-Newton site but could not find this: Do you recommend a
> systematic uncertainty for PN and MOS to be added in quadrature to the
> statistical errros to account for calibration uncertainties? (This, besides
the
> fact that different instruments may give different fluxes, which is
usually
> taken care of by having a multiplicative constant in the model when one
fits
> several instruments simultaneously.)
> 
> I read the latest calibration report, and I thought the number could be
~5%,
but
> perhaps not for the whole energy range. 
> 
> From simultaneous fits with PN and MOS (allowing for a multiplicative
constant
> as I mentioned above), I see that below ~2 keV there is a difference
between
MOS
> and PN that goes from ~ 10% at 0.6 keV to 1-2 % at 2 keV. Above that
energy,
the
> residuals overlap quite okay.
> 
> It would be good if this is included in the thread explaining how to fit
EPIC
> data in Xspec. It would be reasuring for the users to have it somewhere
from
an
> "official source", so to speak.
> 
> Thanks,
> 
> Mariano.
> 
> ----
Dr. Nora Loiseau
XMM-Newton User Support Group

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