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From: wynnho@slac.stanford.edu
Subject: eregionanalyse use of ONTIME versus LIVETIME
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2 replies: 1 2
2 followups: 1 2

Private message: yes  no

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Date: Fri, 24 May 2019 20:06:46 +0200
From: wynnho@slac.stanford.edu
To: xmmhelp@sciops.esa.int
Subject: eregionanalyse use of ONTIME versus LIVETIME
Full_Name: Wynn Ho
Submission from: (NULL) (193.147.152.102)


The outputs of eregionanalyse include (1) exposure time, (2)
background-subtracted source counts, and (3) background-subtracted source
count-rate, where the last is simply (2) divided by (1).  However exposure is
taken from the ONTIME keyword in the fits file, while as I understand it,
LIVETIME is the effective exposure.  So why is eregionanalyse using ONTIME for
the exposure time and hence count-rate instead of LIVETIME?  In the end, I would
like to know what is my source count-rate.

Thanks for your help.


Reply 1

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From: Jacobo Ebrero <xmmhelp@sciops.esa.int>
To: wynnho@slac.stanford.edu
Subject: Re: eregionanalyse use of ONTIME versus LIVETIME (PR#84975)
Date: Mon May 27 11:42:25 2019
Dear Wynn,

To calculate count rates, eregionanalyse uses the EXPOSURE keyword in the header
of the input source image. You may find further details on this task here:

https://xmm-tools.cosmos.esa.int/external/sas/current/doc/eregionanalyse/index.html

Best regards,
Jacobo

----------------------
Dr. Jacobo Ebrero
XMM-Newton SOC
Community Support and Scientific Planning Team


Followup 1

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Date: Mon, 27 May 2019 04:13:02 -0700 (PDT)
From: Wynn Ho <wynnho@slac.stanford.edu>
To: Jacobo Ebrero <xmmhelp@sciops.esa.int>
Subject: Re: eregionanalyse use of ONTIME versus LIVETIME (PR#84975)
Thanks for replying.  I see that in the docs.  However the EXPOSURE
keyword in the header file states that EXPOSURE is the "max of ONTIMEnn
values".  Therefore, my question still stands as to why eregionanalyse
uses ONTIME for EXPOSURE and hence count-rate instead of LIVETIME,
which is the effective exposure?  Seems like LIVETIME is the correct
value to use to calculate the "effective" count-rate.  I could be
wrong and am happy to be corrected.  But I would like to understand
why.  Thanks.

Wynn Ho

On Mon, 27 May 2019, Jacobo Ebrero wrote:

> Dear Wynn,
>
> To calculate count rates, eregionanalyse uses the EXPOSURE keyword in the
header
> of the input source image. You may find further details on this task here:
>
> https://xmm-tools.cosmos.esa.int/external/sas/current/doc/eregionanalyse/index.html
>
> Best regards,
> Jacobo
>
> ----------------------
> Dr. Jacobo Ebrero
> XMM-Newton SOC
> Community Support and Scientific Planning Team
>
> 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: Jacobo rerero <xmmhelp@sciops.esa.int>
To: wynnho@slac.stanford.edu
Subject: Re: eregionanalyse use of ONTIME versus LIVETIME (PR#84975)
Date: Mon May 27 15:22:30 2019
Dear Wynn,

I have checked with the SAS developers and they say that if you want to have the
actual count rate the best is to provide eregionanalyse with an exposure map.
Otherwise the task will take EXPOSURE (the maximum of the sum of GTIs over all
CCDs) as an approximation to the real exposure time. As such, count rates not
derived from an exposure map would be approximate too.

Regards,
Jacobo

----------------------
Dr. Jacobo Ebrero
XMM-Newton SOC
Community Support and Scientific Planning Team


Followup 2

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Date: Mon, 27 May 2019 13:09:22 -0700 (PDT)
From: Wynn Ho <wynnho@slac.stanford.edu>
To: Jacobo rerero <xmmhelp@sciops.esa.int>
Subject: Re: eregionanalyse use of ONTIME versus LIVETIME (PR#84975)
Ok.  Thank you very much for your help.

Dr Wynn Ho
=======================================================
Department of Physics and Astronomy
Haverford College
370 Lancaster Avenue
Haverford, PA 19041, USA
wynnho@slac.stanford.edu

On Mon, 27 May 2019, Jacobo rerero wrote:

> Dear Wynn,
>
> I have checked with the SAS developers and they say that if you want to
have the
> actual count rate the best is to provide eregionanalyse with an exposure
map.
> Otherwise the task will take EXPOSURE (the maximum of the sum of GTIs over
all
> CCDs) as an approximation to the real exposure time. As such, count rates
not
> derived from an exposure map would be approximate too.
>
> Regards,
> Jacobo
>
> ----------------------
> Dr. Jacobo Ebrero
> XMM-Newton SOC
> Community Support and Scientific Planning Team
>
> 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).
>
>


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