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From: j_aquarian_t@yahoo.co.in
Subject: ESAS exposure image and task bin_image
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Date: Tue, 21 May 2019 15:10:37 +0200
From: j_aquarian_t@yahoo.co.in
To: xmmhelp@sciops.esa.int
Subject: ESAS exposure image and task bin_image
Full_Name: Juhi Tiwari
Submission from: (NULL) (193.147.152.102)


Dear SAS help team,

While making images using ESAS, one gets a modeled background (QPB) image and an
exposure image. The exposure image eg.pn-prefix-exp-elow-ehigh.fits has varying
pixel values in units of counts. What does this imply? Are the values different
because of the vignetting effect? - a higher effective exposure in the centre as
compared to the lower values towards the outer regions? even when the exposure
time is the same for all regions of the detector/image.  

While making a background subtracted, exposure corrected image, how does one
scale for the exposure? The ESAS task bin_image does it for the user but I would
like to know how it works. I suppose that the background values are subtracted
from the total counts image but how does one proceed with the exposure
correction?

Also, for the surface brightness analysis of an extended source, can one use the
combined MOS1+MOS2+PN exposure corrected, background subtracted image? - (eg.
rate-elow-ehigh.fits : output of the task bin_image after running the task comb)
(in order to improve statistics and because MOS and PN have similar PSF)  
The pixel values in the rate-elow-ehigh.fits are in units of ct/s/deg^2. How
does one estimate the error in the surface brightness in such a case?

I would be grateful for your help.

Regards,
Juhi


Reply 1

Resend
From: Jacobo Ebrero <xmmhelp@sciops.esa.int>
To: j_aquarian_t@yahoo.co.in
Subject: Re: ESAS exposure image and task bin_image (PR#84965)
Date: Wed May 22 15:24:37 2019
Dear Juhi,

Exposure maps contain all the information about the detector and the telescope,
including effective area, quantum efficiency and vignetting. The differences
between the values at the boresight and at the edges of the image are due to
vignetting.

Related to this, one can correct for exposure using also the exposure map since
that information is also contained in it. The whole procedure to create a
background-substracted exposure-corrected image is described here:

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

but you may also find more information in the ESAS cookbook here:

https://heasarc.gsfc.nasa.gov/docs/xmm/esas/cookbook/xmm-esas.html

where you can find a more detailed description and several examples.

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


Followup 1

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Date: Wed, 22 May 2019 13:38:25 +0000 (UTC)
From: Juhi Tiwari <j_aquarian_t@yahoo.co.in>
To: Jacobo Ebrero <xmmhelp@sciops.esa.int>
Subject: Re: ESAS exposure image and task bin_image (PR#84965)
------=_Part_3978912_1121946806.1558532305692
Content-Type: text/plain; charset=UTF-8
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 Dear Jacobo,
Thanks for your response. I am familiar with the tasks used to create a
background subtracted exposure corrected image described in the links you sent.
I have created the images. The questions in the later part of my message were
slightly different.
While making a background subtracted, exposure corrected image, how does one
scale for the exposure? The ESAS task bin_image does it for the user but I would
like to know how it works. I suppose that the background values are subtracted
from the total counts image but how does one proceed with the exposure
correction?
For eg. the background counts are subtracted from the total counts image. But
how is the exposure correction done? What is done with the pixel values in the
exposure image in order to get the corrected image?
Also, for the surface brightness analysis of an extended source, can one use
thecombined MOS1+MOS2+PN exposure corrected, background subtracted image? - (eg.
rate-elow-ehigh.fits : output of the task bin_image after running the task
comb)(in order to improve statistics and because MOS and PN have similar PSF).
The pixel values in the rate-elow-ehigh.fits are in units of ct/s/deg^2. Howdoes
one estimate the error in the surface brightness in such a case?
The corrected images have units of cts/s/deg^2. How does one find the surface
brightness and the error associated with it in such a case? The counts in each
pixel follow a poisson distribution. But how does one apply the same to these
units? I would like to get an insight into the scaling that is done for exposure
correction in order to solve the above problem.
Thanks,Juhi
    On Wednesday, 22 May, 2019, 6:54:44 pm IST, Jacobo Ebrero
<xmmhelp@sciops.esa.int> wrote:  
 
 Dear Juhi,

Exposure maps contain all the information about the detector and the telescope,
including effective area, quantum efficiency and vignetting. The differences
between the values at the boresight and at the edges of the image are due to
vignetting.

Related to this, one can correct for exposure using also the exposure map since
that information is also contained in it. The whole procedure to create a
background-substracted exposure-corrected image is described here:

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

but you may also find more information in the ESAS cookbook here:

https://heasarc.gsfc.nasa.gov/docs/xmm/esas/cookbook/xmm-esas.html

where you can find a more detailed description and several examples.

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).


  
------=_Part_3978912_1121946806.1558532305692
Content-Type: text/html; charset=UTF-8
Content-Transfer-Encoding: quoted-printable

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class=3D"ydpcb5779afyahoo-style-wrap" style=
=3D"font-family:Helvetica Neue, Helvetica, Arial, sans-serif;font-size:16px=
;"><div></div>
        <div>Dear
Jacobo,</div><div><br></div><div>Thanks for your
response=
. I am familiar with the tasks used to create a background subtracted expos=
ure corrected image described in the links you sent. I have created the ima=
ges. The questions in the later part of my message were slightly different.=
</div><div><br></div><div><div><a
name=3D"themesg" style=3D"color: rgb(0, 0=
, 0); font-size: medium; font-family: Times New Roman;"><pre
style=3D"white=
-space: pre-wrap;">While making a background subtracted, exposure corrected=
 image, how does one
scale for the exposure? The ESAS task bin_image does it for the user but I =
would
like to know how it works. I suppose that the background values are subtrac=
ted
from the total counts image but how does one proceed with the exposure
correction?</pre></a></div><br></div><div>For
eg. the background counts are=
 subtracted from the total counts image. But how is the exposure correction=
 done? What is done with the pixel values in the exposure image in order to=
 get the corrected image?</div><div><a name=3D"themesg"
style=3D"font-size:=
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Message of length 11562 truncated


Reply 2

Resend
From: Jacobo rerero <xmmhelp@sciops.esa.int>
To: j_aquarian_t@yahoo.co.in
Subject: Re: ESAS exposure image and task bin_image (PR#84965)
Date: Wed May 22 17:47:40 2019
Dear Juhi,

The surface brightness for a given pixel is just:

S = [obj - (back + prot + swcx)]/exp

in units of counts/s/pixel where each pixel is 2.5' x 2.5' in solid angle.
If you are binning i pixels then:

S = [sum(obj)i - (sum(back)i + sum(prot)i + sum(swcx)i)]/sum(exp)i

in the same units.

The uncertainty is S_err = sqrt(obj)/exp

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


Followup 2

Compose reply
Download message
Date: Wed, 22 May 2019 17:55:28 +0000 (UTC)
From: Juhi Tiwari <j_aquarian_t@yahoo.co.in>
To: Jacobo rerero <xmmhelp@sciops.esa.int>
Subject: Re: ESAS exposure image and task bin_image (PR#84965)
------=_Part_4037734_198531199.1558547728841
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 7bit

 Dear Jacobo,
Thanks.
Are the values in the exposure image in units of seconds?

Should the pixel values in cts/s/deg^2 units be multiplied with the area of the
pixel in order to get the count rate in that pixel?
Also, can one use a combined PN+MOS1+MOS2 image to derive a surface brightness
profile?
Regards,Juhi




    On Wednesday, 22 May, 2019, 9:17:48 pm IST, Jacobo rerero
<xmmhelp@sciops.esa.int> wrote:  
 
 Dear Juhi,

The surface brightness for a given pixel is just:

S = [obj - (back + prot + swcx)]/exp

in units of counts/s/pixel where each pixel is 2.5' x 2.5' in solid angle.
If you are binning i pixels then:

S = [sum(obj)i - (sum(back)i + sum(prot)i + sum(swcx)i)]/sum(exp)i

in the same units.

The uncertainty is S_err = sqrt(obj)/exp

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).


  
------=_Part_4037734_198531199.1558547728841
Content-Type: text/html; charset=UTF-8
Content-Transfer-Encoding: quoted-printable

<html><head></head><body><div
class=3D"ydpa9313fa5yahoo-style-wrap" style=
=3D"font-family:Helvetica Neue, Helvetica, Arial, sans-serif;font-size:16px=
;"><div></div>
        <div>Dear
Jacobo,</div><div><br></div><div>Thanks.</div><div><br></=
div><div>Are the values in the exposure image in units of
seconds?<br></div=
><div><br></div><div>Should the pixel values in
cts/s/deg^2 units be multip=
lied with the area of the pixel in order to get the count rate in that pixe=
l?</div><div><br></div><div>Also, can one use a
combined PN+MOS1+MOS2 image=
 to derive a surface brightness
profile?</div><div><br></div><div>Regards,<=
/div><div>Juhi</div><div><br></div><div><br></div><div><br></div><div><br><=
/div><div><br></div>
       =20
        </div><div id=3D"ydpb6594d66yahoo_quoted_9528889979"
class=3D"ydpb6=
594d66yahoo_quoted">
            <div style=3D"font-family:'Helvetica Neue', Helvetica, Arial, s=
ans-serif;font-size:13px;color:#26282a;">
               =20
                <div>
                    On Wednesday, 22 May, 2019, 9:17:48 pm IST, Jacobo rere=
ro &lt;xmmhelp@sciops.esa.int&gt; wrote:
                </div>
                <div><br></div>
                <div><br></div>
                <div><div dir=3D"ltr">Dear
Juhi,<br></div><div dir=3D"ltr">=
<br></div><div dir=3D"ltr">The surface brightness for a given
pixel is just=
:<br></div><div dir=3D"ltr"><br></div><div
dir=3D"ltr">S =3D [obj - (back +=
 prot + swcx)]/exp<br></div><div
dir=3D"ltr"><br></div><div dir=3D"ltr">in =
units of counts/s/pixel where each pixel is 2.5' x 2.5' in solid
angle.<br>=
</div><div dir=3D"ltr">If you are binning i pixels
then:<br></div><div dir=
=3D"ltr"><br></div><div dir=3D"ltr">S =3D [sum(obj)i -
(sum(back)i + sum(pr=
ot)i + sum(swcx)i)]/sum(exp)i<br></div><div
dir=3D"ltr"><br></div><div dir=
=3D"ltr">in the same units.<br></div><div
dir=3D"ltr"><br></div><div dir=3D=
"ltr">The uncertainty is S_err =3D sqrt(obj)/exp<br></div><div
dir=3D"ltr">=
<br></div><div
dir=3D"ltr">Regards,<br></div><div
dir=3D"ltr">Jacobo<br></d=
iv><div dir=3D"ltr">----------------------<br></div><div
dir=3D"ltr">Dr. Ja=
cobo Ebrero<br></div><div dir=3D"ltr">XMM-Newton
SOC<br></div><div dir=3D"l=
tr">Community Support and Scientific Planning
Team<br></div><div dir=3D"ltr=
"><br></div><div dir=3D"ltr">This message is intended only
for the recipien=
t(s) named above. It may contain proprietary information
and/or<br></div><d=
iv dir=3D"ltr">protected content. Any unauthorised disclosure, use, retenti=
on or dissemination is prohibited. If you have
received<br></div><div dir=

Message of length 5622 truncated


Reply 3

Resend
From: Jacobo Ebrero <xmmhelp@sciops.esa.int>
To: j_aquarian_t@yahoo.co.in
Subject: Re: ESAS exposure image and task bin_image (PR#84965)
Date: Thu May 23 11:10:04 2019
Dear Juhi,

Yes, the values of S and S_err must be multiplied by 2.0736e6, which is scale
factor to convert to counts/s/deg^2, and is equal to the reciprocal of the pixel
area 2.5" x 2.5".

Regards,
Jacobo

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

Up to top level
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