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From: jcjiang12@gmail.com
Subject: Combine EPIC spectra
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Date: Thu, 20 Jul 2017 10:22:48 GMT
From: jcjiang12@gmail.com
To: xmmhelp@sciops.esa.int
CC: jcjiang12@gmail.com
Subject: Combine EPIC spectra
Full_Name: Jiachen Jiang
Submission from: (NULL) (131.111.69.75)


Dear Sir/Madam,

I just want to ask in the case of one observation consisting of two EPIC
exposures with different modes, such as different filters or frames, whether it
is right or not to combine them using addspec and addrmf (to correct the
response matrix according to the exposures)?

Thanks a lot.

Jiachen


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From: Lucia Ballo <xmmhelp@sciops.esa.int>
To: jcjiang12@gmail.com
Subject: Re: Combine EPIC spectra (PR#82014)
Date: Fri Jul 21 12:00:38 2017
Dear Jiachen,

  as a general rule and taking into account the different spectral
  response of the three EPIC cameras, we recommend to keep each
  spectrum separate and combine them only in the analysis. XSPEC and
  most programs for X-rays spectra analysis allow to do simultaneous
  fits to spectra from different epochs and/or instruments. 

  Note that there is no statistical gain in adding up the spectra
  before the fit with respect to fit them all simultaneously;
  however, using individual spectra/response/effective area
  guarantees a correct comparison between model prediction and
  actual data.

  

  If you still want to combine the spectra, the ftools programs that
  you mention can add spectra and combine rmf/arf but they are not part 
  of XMM-Newton SAS. You may use instead the SAS task epicspecombine,
  designed to produce combined spectra. Please find a step-by-step
  description of how to proceed in this thread:

  https://www.cosmos.esa.int/web/xmm-newton/sas-thread-epic-merging

  

  I hope that this can help you; otherwise please do not hesitate to
  contact us again.

  
With kind regards,
  Lucia

--
   Dr Lucia Ballo 
   XMM-Newton Science Operations Centre
   Community Support and Scientific Planning Team

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