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From: prakash@ncra.tifr.res.in
Subject: Source extraction region sizes
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Date: Thu, 9 Aug 2018 08:42:05 GMT
From: prakash@ncra.tifr.res.in
To: xmmhelp@sciops.esa.int
CC: prakash@ncra.tifr.res.in
Subject: Source extraction region sizes
Full_Name: Prakash Arumugasamy
Submission from: (NULL) (193.147.152.102)


Dear helpdesk members,

Could you please let me know if there is a minimum source extraction radius (in
pn and MOS) recommended for spectral extraction?
For instance, will the spectrum be inaccurate if we choose circular regions of
radius 15" or 10" (300 or 200 in physical units)?
For weak sources, such small region sizes (also recommended by eregionanalyse
task) seem to give the highest S/N spectra bins, especially above ~1 keV.
Wouldn't choosing a large radius region for spectral extraction, producing
source contribution below 40-50% in those bins, be statistically unreliable for
spectral fitting?

Thanks,
Prakash A.


Reply 1

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From: Nora Loiseau <xmmhelp@sciops.esa.int>
To: prakash@ncra.tifr.res.in
Subject: Re: Source extraction region sizes (PR#83821)
Date: Thu Aug  9 13:59:54 2018
Dear Prakash,

The SAS task eregionanalyse would be appropriate for your purpose, see:
https://xmm-tools.cosmos.esa.int/external/sas/current/doc/eregionanalyse/node3.html

Otherwise you can also check the literature, for example:

https://www.aanda.org/articles/aa/pdf/2015/04/aa25124-14.pdf

https://www.aanda.org/articles/aa/pdf/2012/11/aa19532-12.pdf

Regards,

Nora

> 
> Could you please let me know if there is a minimum source extraction radius
(in
> pn and MOS) recommended for spectral extraction?
> For instance, will the spectrum be inaccurate if we choose circular regions
of
> radius 15" or 10" (300 or 200 in physical units)?
> For weak sources, such small region sizes (also recommended by
eregionanalyse
> task) seem to give the highest S/N spectra bins, especially above ~1 keV.
> Wouldn't choosing a large radius region for spectral extraction, producing
> source contribution below 40-50% in those bins, be statistically unreliable
for
> spectral fitting?
> 
> Thanks,
> Prakash A.
> 
> ----
Dr. Nora Loiseau
XMM-Newton User Support Group


Followup 1

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Date: Thu, 09 Aug 2018 21:28:00 +0530
From: prakash <prakash@ncra.tifr.res.in>
To: Nora Loiseau <xmmhelp@sciops.esa.int>
Subject: Re: Source extraction region sizes (PR#83821)
Dear Nora,

I do use the eregionanalyse task to get the optimal region sizes.
The references do not really discuss potential problems of the 
suitability of small extraction apertures.

My only concern is that a very small region ~ 10" radius might severely 
undersample the PSF but give the highest S/N for a weak source.
Is there any known problem with spectra extracted from such small 
apertures?

Could you please confirm if an extraction region of 10" (from 
eregionanalyse) may be used for spectral extraction in the entire 0.2-10 
keV range?
If not, then is there a minimum region size that one needs to maintain?

Thanks,
Prakash.

On 2018-08-09 19:29, Nora Loiseau wrote:
> Dear Prakash,
> 
> The SAS task eregionanalyse would be appropriate for your purpose, see:
> https://xmm-tools.cosmos.esa.int/external/sas/current/doc/eregionanalyse/node3.html
> 
> Otherwise you can also check the literature, for example:
> 
> https://www.aanda.org/articles/aa/pdf/2015/04/aa25124-14.pdf
> 
> https://www.aanda.org/articles/aa/pdf/2012/11/aa19532-12.pdf
> 
> Regards,
> 
> Nora
> 
>> 
>> Could you please let me know if there is a minimum source extraction 
>> radius
> (in
>> pn and MOS) recommended for spectral extraction?
>> For instance, will the spectrum be inaccurate if we choose circular 
>> regions
> of
>> radius 15" or 10" (300 or 200 in physical units)?
>> For weak sources, such small region sizes (also recommended by 
>> eregionanalyse
>> task) seem to give the highest S/N spectra bins, especially above ~1 
>> keV.
>> Wouldn't choosing a large radius region for spectral extraction, 
>> producing
>> source contribution below 40-50% in those bins, be statistically 
>> unreliable
> for
>> spectral fitting?
>> 
>> Thanks,
>> Prakash A.
>> 
>> ----
> Dr. Nora Loiseau
> XMM-Newton User Support Group
> 
> This message is intended only for the recipient(s) named above. It may
> contain proprietary information and/or
> protected content. Any unauthorised disclosure, use, retention or
> dissemination is prohibited. If you have received
> this e-mail in error, please notify the sender immediately. ESA
> applies appropriate organisational measures to protect
> personal data, in case of data privacy queries, please contact the ESA
> Data Protection Officer (dpo@esa.int).



Reply 2

Resend
From: Nora Loiseau <xmmhelp@sciops.esa.int>
To: prakash@ncra.tifr.res.in
Subject: Re: Source extraction region sizes (PR#83821)
Date: Thu Aug  9 16:12:52 2018
Dear Prakash,

I consulted the SAS expert and he says that 10" is OK, but should not be smaller
than that, 10" is the minimum radius to be used.

Best regards,

Nora

> 
> I do use the eregionanalyse task to get the optimal region sizes.
> The references do not really discuss potential problems of the 
> suitability of small extraction apertures.
> 
> My only concern is that a very small region ~ 10" radius might severely 
> undersample the PSF but give the highest S/N for a weak source.
> Is there any known problem with spectra extracted from such small 
> apertures?
> 
> Could you please confirm if an extraction region of 10" (from 
> eregionanalyse) may be used for spectral extraction in the entire 0.2-10 
> keV range?
> If not, then is there a minimum region size that one needs to maintain?
> 
> Thanks,
> Prakash.
> 
> On 2018-08-09 19:29, Nora Loiseau wrote:
>> Dear Prakash,
>> 
>> The SAS task eregionanalyse would be appropriate for your purpose,
see:
>> https://xmm-tools.cosmos.esa.int/external/sas/current/doc/eregionanalyse/node3.html
>> 
>> Otherwise you can also check the literature, for example:
>> 
>> https://www.aanda.org/articles/aa/pdf/2015/04/aa25124-14.pdf
>> 
>> https://www.aanda.org/articles/aa/pdf/2012/11/aa19532-12.pdf
>> 
>> Regards,
>> 
>> Nora
>> 
>>> 
>>> Could you please let me know if there is a minimum source
extraction 
>>> radius
>> (in
>>> pn and MOS) recommended for spectral extraction?
>>> For instance, will the spectrum be inaccurate if we choose circular

>>> regions
>> of
>>> radius 15" or 10" (300 or 200 in physical units)?
>>> For weak sources, such small region sizes (also recommended by 
>>> eregionanalyse
>>> task) seem to give the highest S/N spectra bins, especially above
~1 
>>> keV.
>>> Wouldn't choosing a large radius region for spectral extraction, 
>>> producing
>>> source contribution below 40-50% in those bins, be statistically 
>>> unreliable
>> for
>>> spectral fitting?
>>> 
>>> Thanks,
>>> Prakash A.
>>> 
>>> ----
>> Dr. Nora Loiseau
>> XMM-Newton User Support Group
>> 
>> This message is intended only for the recipient(s) named above. It may
>> contain proprietary information and/or
>> protected content. Any unauthorised disclosure, use, retention or
>> dissemination is prohibited. If you have received
>> this e-mail in error, please notify the sender immediately. ESA
>> applies appropriate organisational measures to protect
>> personal data, in case of data privacy queries, please contact the ESA
>> Data Protection Officer (dpo@esa.int).
> 
> ----
Dr. Nora Loiseau
XMM-Newton User Support Group

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