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From: aszostek@slac.stanford.edu
Subject: normalization between instruments
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Date: Tue, 4 Oct 2011 00:17:40 GMT
From: aszostek@slac.stanford.edu
To: xmmhelp@sciops.esa.int
Cc: aszostek@slac.stanford.edu
Subject: normalization between instruments
Full_Name: anna szostek
Submission from: (NULL) (198.129.216.106)


Hi,
I am trying to fit a spectrum of a galaxy cluster from ann annulus. I want to
include in my fit the rosat spectrum to get better constraints on extragalactic
background. I read all manuals and a few papers and I understand the general
procedure, however it is not clear to me how should I normalize the XMM
instruments with respect to the Rosat. Lets say the model is
C1*C2*(background+source). What should be the values of C1 and C2?

For my spectra the area of each instrument in arcmin^2 is:
mos1 - 13.16
mos2 - 12.93
pn - 12.09
rosat - 34416

the values were obtained from proton_scale and from online X-ray background
tool.

Here are my questions and uncertainties:
- I obtained rosat spectrum from heasarc X-ray background tool from an annulus
between 1-2 deg. As far as i understand the rosat spectrum is in units of
counts/cm2/s/arcmin^2 while the xmm spectra are counts/cm2/s is it true? 
- If yes, how do I set C1 and C2?
- Should I set C1 for the values of the area given above and fix it during the
fit?
- Should I set somehow backscal keywords in each file? now XMM files have
backscal set, but rosat is set to 1.
- Should I set C2 as 1 for rosat and fit the remaining instruments?
- If I fit C1 to the values above, C2 for rosat = 1, my C2 values for xmm are
huge ~ 5e5. Is it correct?
- From de Luca Molendi et al. 2004 it says that the rosat flux between 2-10 keV
should be 2.24e-11 erg/cm2/s/deg2 so if calculate the flux of my extragalactic
component only it should be that value, yes?
- should the rosat C1 and C2 all be equal 1?
- do the values of keywords backscal are important for the values of C1 and C2?
Or this is only to correctly subtract background from provided file but is not
taken into account between different instruments?

Best wishes
Anna




Reply 1

Resend
From: Ignacio de la Calle <xmmhelp@sciops.esa.int>
To: aszostek@slac.stanford.edu
Subject: Re: normalization between instruments (PR#48797)
Date: Tue Oct  4 15:32:02 2011
Dear Anna,

In order to understand you question, I would need to understand better the
overall astrophysical background of your question. Hence I can only answer in a
very general context. Assuming that you wish to include an estimate of the
astrophysical background underneath the XMM-Newton annulus cluster spectrum
using a ROSAT spectrum, I would recommend you to add an additional component
describing the background spectra as measured by ROSAT. 

In practical terms you could proceed along these lines:

- extract the ROSAT spectra and response files using the data reduction and
analysis procedures as in the ROSAT documentation (on which we cannot provide
you with much support, I am afraid)

- model the ROSAT spectrum using the most appropriate physical models (a
combination of thermal components has been used in the past, although in recent
years the role of Solar Wind Charge Exchange has been discovered to be more
prominent as originally thought, as you surely know; many recent papers by
Snowden and Kuntz discuss this point. Again, I cannot provide further support as
this step involves taking decission
based on physics which only you can asses)

- add the model determined in the previous step to the spectral model fitting
your XMM-Newton cluster data

This leaves untouched the issue of the relative cross-calibration between
XMM-Newton 
and ROSAT. However, as far as I know, there is no systematic study comparing the

effective area systematics between the EPIC and the ROSAT/PSPC. A conservative 
approach should allow a ~10% relative flux mis-calibration at any energies.

Please keep in mind that the kind of questions you ask are of a physics nature
rather than technical questions, and that ultimately it is your decision to
proceed one way or another.

Regards,

Ignacio de la Calle
XMM-Newton SOC


> Full_Name: anna szostek
> Submission from: (NULL) (198.129.216.106)
> 
> 
> Hi,
> I am trying to fit a spectrum of a galaxy cluster from ann annulus. I want
to
> include in my fit the rosat spectrum to get better constraints on
extragalactic
> background. I read all manuals and a few papers and I understand the
general
> procedure, however it is not clear to me how should I normalize the XMM
> instruments with respect to the Rosat. Lets say the model is
> C1*C2*(background+source). What should be the values of C1 and C2?
> 
> For my spectra the area of each instrument in arcmin^2 is:
> mos1 - 13.16
> mos2 - 12.93
> pn - 12.09
> rosat - 34416
> 
> the values were obtained from proton_scale and from online X-ray
background
> tool.
> 
> Here are my questions and uncertainties:
> - I obtained rosat spectrum from heasarc X-ray background tool from an
annulus
> between 1-2 deg. As far as i understand the rosat spectrum is in units of
> counts/cm2/s/arcmin^2 while the xmm spectra are counts/cm2/s is it true? 
> - If yes, how do I set C1 and C2?
> - Should I set C1 for the values of the area given above and fix it during
the
> fit?
> - Should I set somehow backscal keywords in each file? now XMM files have
> backscal set, but rosat is set to 1.
> - Should I set C2 as 1 for rosat and fit the remaining instruments?
> - If I fit C1 to the values above, C2 for rosat = 1, my C2 values for xmm
are
> huge ~ 5e5. Is it correct?
> - From de Luca Molendi et al. 2004 it says that the rosat flux between 2-10
keV
> should be 2.24e-11 erg/cm2/s/deg2 so if calculate the flux of my
extragalactic
> component only it should be that value, yes?
> - should the rosat C1 and C2 all be equal 1?
> - do the values of keywords backscal are important for the values of C1 and
C2?
> Or this is only to correctly subtract background from provided file but is
not
> taken into account between different instruments?
> 
> Best wishes
> Anna
> 
> 
> 
> 


Followup 1

Compose reply
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From: "Szostek, Anna" <aszostek@slac.stanford.edu>
To: Ignacio de la Calle <xmmhelp@sciops.esa.int>
Date: Wed, 5 Oct 2011 12:38:45 -0700
Subject: Re: normalization between instruments (PR#48797)
Ok, thank you very much for the reply.

Anna


On Oct 4, 2011, at 8:32 AM, Ignacio de la Calle wrote:

> Dear Anna,
> 
> In order to understand you question, I would need to understand better the
> overall astrophysical background of your question. Hence I can only answer
in a
> very general context. Assuming that you wish to include an estimate of the
> astrophysical background underneath the XMM-Newton annulus cluster spectrum
> using a ROSAT spectrum, I would recommend you to add an additional
component
> describing the background spectra as measured by ROSAT. 
> 
> In practical terms you could proceed along these lines:
> 
> - extract the ROSAT spectra and response files using the data reduction and
> analysis procedures as in the ROSAT documentation (on which we cannot
provide
> you with much support, I am afraid)
> 
> - model the ROSAT spectrum using the most appropriate physical models (a
> combination of thermal components has been used in the past, although in
recent
> years the role of Solar Wind Charge Exchange has been discovered to be more
> prominent as originally thought, as you surely know; many recent papers by
> Snowden and Kuntz discuss this point. Again, I cannot provide further
support as
> this step involves taking decission
> based on physics which only you can asses)
> 
> - add the model determined in the previous step to the spectral model
fitting
> your XMM-Newton cluster data
> 
> This leaves untouched the issue of the relative cross-calibration between
> XMM-Newton 
> and ROSAT. However, as far as I know, there is no systematic study
comparing the
> 
> effective area systematics between the EPIC and the ROSAT/PSPC. A
conservative 
> approach should allow a ~10% relative flux mis-calibration at any energies.
> 
> Please keep in mind that the kind of questions you ask are of a physics
nature
> rather than technical questions, and that ultimately it is your decision to
> proceed one way or another.
> 
> Regards,
> 
> Ignacio de la Calle
> XMM-Newton SOC
> 
> 
>> Full_Name: anna szostek
>> Submission from: (NULL) (198.129.216.106)
>> 
>> 
>> Hi,
>> I am trying to fit a spectrum of a galaxy cluster from ann annulus. I
want to
>> include in my fit the rosat spectrum to get better constraints on
> extragalactic
>> background. I read all manuals and a few papers and I understand the
general
>> procedure, however it is not clear to me how should I normalize the XMM
>> instruments with respect to the Rosat. Lets say the model is
>> C1*C2*(background+source). What should be the values of C1 and C2?
>> 
>> For my spectra the area of each instrument in arcmin^2 is:
>> mos1 - 13.16
>> mos2 - 12.93
>> pn - 12.09
>> rosat - 34416
>> 
>> the values were obtained from proton_scale and from online X-ray
background
>> tool.
>> 
>> Here are my questions and uncertainties:
>> - I obtained rosat spectrum from heasarc X-ray background tool from an
> annulus
>> between 1-2 deg. As far as i understand the rosat spectrum is in units
of
>> counts/cm2/s/arcmin^2 while the xmm spectra are counts/cm2/s is it
true? 
>> - If yes, how do I set C1 and C2?
>> - Should I set C1 for the values of the area given above and fix it
during
> the
>> fit?
>> - Should I set somehow backscal keywords in each file? now XMM files
have
>> backscal set, but rosat is set to 1.
>> - Should I set C2 as 1 for rosat and fit the remaining instruments?
>> - If I fit C1 to the values above, C2 for rosat = 1, my C2 values for
xmm are
>> huge ~ 5e5. Is it correct?
>> - From de Luca Molendi et al. 2004 it says that the rosat flux between
2-10
> keV
>> should be 2.24e-11 erg/cm2/s/deg2 so if calculate the flux of my
> extragalactic
>> component only it should be that value, yes?
>> - should the rosat C1 and C2 all be equal 1?
>> - do the values of keywords backscal are important for the values of C1
and
> C2?
>> Or this is only to correctly subtract background from provided file but
is
> not
>> taken into account between different instruments?
>> 
>> Best wishes
>> Anna
>> 
>> 
>> 
>> 
> 
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