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From: Kevin Hurley <khurley@ssl.berkeley.edu>
Subject: XMM/XSPEC problem
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Date: Wed, 11 May 2005 13:22:55 -0700 (PDT)
From: Kevin Hurley <khurley@ssl.berkeley.edu>
Subject: XMM/XSPEC problem
To: xmmhelp@xmm.vilspa.esa.es
Cc: khurley@scylla2.ssl.berkeley.edu
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Dear Helpdesk,

I have found a curious problem with XMM spectra in XSPEC.  When
I input a data spectrum and plot it (without doing any spectral
fitting) every channel from 1 to 4096 appears to have at least
one count in it.  I known that these are not real counts, because
XSPEC says that there are only 200 photons in the data file.  I've
seen this now with two XMM data sets; I don't think I've ever seen
it with data from other instruments.  Have you encountered this before?
I've attached two files that illustrate the problem.

Thanks for your help.

Kevin
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Reply 1

Resend
From: Pedro M. Rodriguez Pascual <xmmhelp@xmm.vilspa.esa.es>
To: khurley@ssl.berkeley.edu
Subject: Re: XMM/XSPEC problem (PR#17726)
Date: Thu May 12 07:52:36 2005
Dear Kevin, 

Please note that you are plotting data AND error bars. XSPEC arbitrarily gives
an error value of unity to those channels with no counts. What you call "not
real counts" are indeed the error bars XSPEC associates to channels with no
counts.

Within iplot, "PLT> Error Y OFF" will supress error bars and all the "not
real
counts" will disappear.

Sincerely, 

Pedro

> 
> Dear Helpdesk,
> 
> I have found a curious problem with XMM spectra in XSPEC.  When
> I input a data spectrum and plot it (without doing any spectral
> fitting) every channel from 1 to 4096 appears to have at least
> one count in it.  I known that these are not real counts, because
> XSPEC says that there are only 200 photons in the data file.  I've
> seen this now with two XMM data sets; I don't think I've ever seen
> it with data from other instruments.  Have you encountered this before?
> I've attached two files that illustrate the problem.
> 
> Thanks for your help.
> 
> Kevin

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