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From: Giovanni Fossati <gfossati@rice.edu>
Subject: "usable" quality factor in observation log
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2 replies: 1 2
1 followups: 1

Private message: yes  no

Notes:

Notification:


Date: Wed, 23 Mar 2005 15:06:22 -0600 (CST)
From: Giovanni Fossati <gfossati@rice.edu>
Subject: "usable" quality factor in observation log
To: XMM HelpDesk <xmmhelp@xmm.vilspa.esa.es>
					      Wednesday March 23, 2005
Hello,
I was looking at the log of the observations performed with the "observation
log browser", and I could not find anywhere an explanation of the color
coding of the quality factor of the different exposures.
I see from the help that orange is "usable"... but what does that mean?
Is it a sign of technical problems or simply due to the ratio of real exposure
to scheduled exposure, for instance.
Thanks a lot.
All the best,
 		Giovanni

------------------------------------------------------------------------------
 Dr. Giovanni Fossati                            +---------------------------+
 Dept. of Physics and Astronomy, MS 108          | Ph    : (713)-348-3425    |
 Rice University                                 | Fax   : (713)-348-5143    |
 6100 Main street, Houston, TX 77005, USA        | e-mail: gfossati@rice.edu |
-------------------------------------------------+---------------------------+


Reply 1

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From: Matthias Ehle <xmmhelp@xmm.vilspa.esa.es>
To: gfossati@rice.edu
Subject: Re: "usable" quality factor in observation log (PR#17415)
Date: Mon Mar 28 10:15:53 2005
Dear Giovanni,

"usable" means that for any reason the exposure was not exactly performed
as it was scheduled by the mission planners. For example we sometimes have 
the case that an EPIC exposure has to be stopped (and evtl. re-started) due
to high radiation alerts. Or it might have suffered from telemetry drops
or ground station un-availability. All this may lead to a less than
scheduled exposure time but the data nevertheless can be processed with the
SAS software.

Additional info might be given in the "General Observation Comments"
available through the log browser, too.

Cheers,
   Matthias


--
   Dr Matthias Ehle 
   XMM-Newton User Support Group
   European Space Astronomy Centre


Followup 1

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Date: Mon, 28 Mar 2005 19:07:31 -0600 (CST)
From: Giovanni Fossati <gfossati@rice.edu>
Subject: Re: "usable" quality factor in observation log (PR#17415)
To: Matthias Ehle <xmmhelp@xmm.vilspa.esa.es>
					      Monday March 28, 2005
Dear Matthias,
thanks for the reply.
This is what is reported in the comments online:

MOS1 CCD6 does not accumulate since 2005-03-09@01:30.
PN experienced full scientific buffer from 2005-03-21@23:52 to 2005-03-22@02:58.

I see that the first warning is clearly a general issue.
The second one sounds a lot more important, making me think to some serious 
brightness problem.  On the other hand the same warning is also reported for
all other observations of revolution 967.
What should I make of it?

Bottom line is that I should be able to use the data, probably in a less
than optimal way.   Since this is my first XMM observation (it was a stroke of
luck...a C target, but more should come this year, A's and B's), I am not 
very familiar with possible issues and consequent difficulties with the
analysis, and I would really appreciate if you could tell more about this.
It is also important to know as much as possible because NASA is going to
provide
some minimal financial support also for C targets, and that also depends on 
how trivial or difficult the analysis will be.
Thanks a lot.
All the best,

 		Giovanni
------------------------------------------------------------------------------
 Dr. Giovanni Fossati                            +---------------------------+
 Dept. of Physics and Astronomy, MS 108          | Ph    : (713)-348-3425    |
 Rice University                                 | Fax   : (713)-348-5143    |
 6100 Main street, Houston, TX 77005, USA        | e-mail: gfossati@rice.edu |
-------------------------------------------------+---------------------------+

On Mon, 28 Mar 2005, Matthias Ehle wrote:

> Dear Giovanni,
> 
> "usable" means that for any reason the exposure was not exactly performed
> as it was scheduled by the mission planners. For example we sometimes have 
> the case that an EPIC exposure has to be stopped (and evtl. re-started) due
> to high radiation alerts. Or it might have suffered from telemetry drops
> or ground station un-availability. All this may lead to a less than
> scheduled exposure time but the data nevertheless can be processed with the
> SAS software.
> 
> Additional info might be given in the "General Observation Comments"
> available through the log browser, too.
> 
> Cheers,
>    Matthias



Reply 2

Resend
From: Matthias Ehle <xmmhelp@xmm.vilspa.esa.es>
To: gfossati@rice.edu
Subject: Re: "usable" quality factor in observation log (PR#17415)
Date: Tue Mar 29 08:19:24 2005
Dear Giovanni,
 
> MOS1 CCD6 does not accumulate since 2005-03-09@01:30.

yes, this is the general comment releated to the EPIC MOS1 Event of Rev. 961
(see XMM-Newton Newsletter#48).

> PN experienced full scientific buffer from 2005-03-21@23:52 to
2005-03-22@02:58.

There might be two reasons for a full scientific buffer:
a) the source is very bright and a faster readout mode would better have been
used.
b) the radiation background is high.

In both cases the PN receives so many events per readout frame that these
cannot properly be handled be the on board electronics. 

If so, the PN camera switches into the so-called "counting mode" where no 
scientific data is recorded (only a counter measuring the received number of 
events and of course the normal housekeeping data). 
For the scientific output this just means that during such periods there
are no scientific data from the PN (similar to a non-good time interval).
The event list and related keywords (e.g. exposure time) take all this into
account
so that the received scientific event file can be processed in a standard 
way (it just does not have entries for the times when the PN camera was in 
counting mode).

The fact that full scientific buffer is also reported as you say for all other
observations of revolution 967 is a clear indication that the radiation
background
was high in this orbit. Please check the SAS Users Guide on how to inspect and
clean
the data for high radiation periods which probably are still present in the 
remaining PN data.

In summary: it should be possible to process the data (after checking/removing 
of high background periods) in the standard way.

Cheers,
  Matthias

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