Up to top level
AO15   AO16   AO17   AO18   AO19   Backgrounds   Calibration   Conference   Data   Docs   EPICMOS   EPICpn   Feedback   Gallery   Misc   OM   Pending   PhD_Theses   Publications   RGS   RadMonitor   SAS_Hardware   SAS_WS   SASv16.0   SASv16.0_Installation   SASv16.1   SASv16.1_Installation   SASv17.0   SASv17.0_Installation   SASv18.0   SASv18.0_Installation   SciSim   Simulators_other   Suggestions   Trash   Visibility   XMM-bouncing   XMM-news   XRPS   XSA   esas   incoming  

Logged in as guest

Viewing esas/47548
Full headers

From: aszostek@slac.stanford.edu
Subject: High proton background -
Compose reply
Download message
Move To:
1 replies: 1
1 followups: 1

Private message: yes  no

Notes:

Notification:


Date: Tue, 15 Mar 2011 22:25:27 GMT
From: aszostek@slac.stanford.edu
To: xmmhelp@sciops.esa.int
Cc: aszostek@slac.stanford.edu
Subject: High proton background - 
Full_Name: Anna Szostek
Submission from: (NULL) (198.129.217.198)


Dear Helpdesk Team,
I am working on observation 0610980101 using esas in sas v10.0. The observation
is highly contaminated by background proton flares. The cleaning removes more
than half of the data and the remaining still is "extremely contaminated" as
measured by Molendi et al. script found here: 

http://xmm2.esac.esa.int/external/xmm_sw_cal/background/epic_scripts.shtml#flare


Some of the problems I have with this data:

- The mos1 and mos2 images differ quite a lot. In particular quite bright source
in mos1 is only a fuzzy faint patch in mos2. 

- The comparison of the spectrum with a quiescent background spectrum does not
look good. Observed spectrum is almost powerlaw and is quite high with respect
to quiescent particle background spectrum ( I did not run mos-spectra at the
same time as in one of my previous submissions)

- After combining mos images and correction for exposure (output of adapt_900
without including particle and proton corrections), the images have excess
emission at the edge of an image. It must be something with exposure because
even if I don't correct for particle and proton background the effect is still
there. 

- High energy (2-8 keV) combined and smoothed image has badly handled region
above missing ccd#6. I checked the component images created by comb (exposure,
proton map, QPB map) but don't see anything wrong there. 

The images showing these problems can be found here:
https://docs.google.com/document/pub?id=17VSHckExN6-OWQKyqbjVJhq2xCnZGu_xuDK4SugUxX8

What could be the reason for the above problems? Are these signatures of the
high proton background or something else.

Are these observations usable?


Best regards
Anna



Reply 1

Resend
From: Ignacio de la Calle <xmmhelp@sciops.esa.int>
To: aszostek@slac.stanford.edu
Subject: Re: High proton background - (PR#47548)
Date: Wed Mar 16 13:20:13 2011
Dear Anna,

We had an answer from the ESAS developers. First, have a look at this site
that is being put together with some watchout items.

http://heasarc.gsfc.nasa.gov/docs/xmm/xmmhp_xmmesas.html

The filtering only will get rid of the part of the data where the soft
proton (SP) background is fluctuating. Not all SP contamination can be removed,
and some observations are just completely ruined. This is where you need to
judge and determine just how much contamination you can live with. This
observation is particularly bad.

In reply to you questions:

> - The mos1 and mos2 images differ quite a lot. In particular quite bright
source
> in mos1 is only a fuzzy faint patch in mos2. 

This has to be an instrument artifact. Could the bright source lie
on a CCD gap or an excluded bad column for the MOS2? Has the same
scaling being used for both detectors ? There are other sources in the 
MOS2 image that look fainter than those in MOS1 so it may be a case 
of inconsistent scaling.

> - The comparison of the spectrum with a quiescent background spectrum does
not
> look good. Observed spectrum is almost powerlaw and is quite high with
respect
> to quiescent particle background spectrum ( I did not run mos-spectra at
the
> same time as in one of my previous submissions)

This is the signature of strong residual soft proton contamination.
Very bad residual contamination.

> - After combining mos images and correction for exposure (output of
adapt_900
> without including particle and proton corrections), the images have excess
> emission at the edge of an image. It must be something with exposure
because
> even if I don't correct for particle and proton background the effect is
still
> there. 

This a known effect, which has been documented. The particle background (PB) and

soft proton (SP) background are distributed differently across the detectors
than
a vignetted flat field X-ray source, and the vignetting effect is included 
in the exposure maps. The PB and SP backgrounds have a relatively flat
distribution across the detectors so when they are corrected (divided by)
the exposure map you get an inverted exposure map where the outside edge 
is brighter than the center. This will most strongly be seen at higher
energies and in observations with a strong residual SP background which is
not properly subtracted.

> - High energy (2-8 keV) combined and smoothed image has badly handled
region
> above missing ccd#6. I checked the component images created by comb
(exposure,
> proton map, QPB map) but don't see anything wrong there. 

When the residual backgrounds are this strong there are going to be artefacts.



Followup 1

Compose reply
Download message
From: "Szostek, Anna" <aszostek@slac.stanford.edu>
To: Ignacio de la Calle <xmmhelp@sciops.esa.int>
Date: Mon, 21 Mar 2011 12:37:22 -0700
Subject: Re: High proton background - (PR#47548)
Dear Ignacio,
Thank you very much for detailed answer. I looked into some suggested directions
and have an additional question:

> This has to be an instrument artifact. Could the bright source lie on a CCD
gap or an excluded bad column for the MOS2? Has the same scaling being used for
both detectors ? There are other sources in the 
> MOS2 image that look fainter than those in MOS1 so it may be a case of
inconsistent scaling.
> 

I checked and the central source does not lie on to of the bad column. And yes
there are other sources in the field that differ between mos1 and mos2. The
event files which produce differing images are created by emchain and mos-filter
tasks as part of the esas analysis. How do I control the scaling of detectors? I
didn't change the default parameters. Could the difference be caused by the
differences in background flare cleaning if mos1 and mos2 have different events
rejected?


> This a known effect, which has been documented. The particle background
(PB) and
> soft proton (SP) background are distributed differently across the
detectors
> than a vignetted flat field X-ray source, and the vignetting effect is
included 
> in the exposure maps. The PB and SP backgrounds have a relatively flat
> distribution across the detectors so when they are corrected (divided by)
> the exposure map you get an inverted exposure map where the outside edge 
> is brighter than the center. This will most strongly be seen at higher
> energies and in observations with a strong residual SP background which is
> not properly subtracted.
> 

Could you point me to the document which describes this problem?

Best regards
Anna


Up to top level
AO15   AO16   AO17   AO18   AO19   Backgrounds   Calibration   Conference   Data   Docs   EPICMOS   EPICpn   Feedback   Gallery   Misc   OM   Pending   PhD_Theses   Publications   RGS   RadMonitor   SAS_Hardware   SAS_WS   SASv16.0   SASv16.0_Installation   SASv16.1   SASv16.1_Installation   SASv17.0   SASv17.0_Installation   SASv18.0   SASv18.0_Installation   SciSim   Simulators_other   Suggestions   Trash   Visibility   XMM-bouncing   XMM-news   XRPS   XSA   esas   incoming  

Logged in as guest


Please make your (short) question the subject of your request!


Web interface using JitterBug ... back to the XMM home page