XMM-Newton Science Analysis System
epicbscalgen (ccftools-1.34) [xmmsas_20060628_1801-7.0.0]
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The usage of the task is very straightforward and the possibilities
of making mistakes are small. The following points should be noted
is a meta-task that makes use of a couple of other
A basic familiarity with the functionality provided by these tasks is
recommended. This is not a pre-requisite of making use of epicbscalgen
- It is recommended to run the task on a verbosity level 5 for getting
a feeling for the operations carried out in each iteration.
- For controlling the convergence process it is usually advantageous
to re-direct the standard output and error stream into a file and
monitor its contents. This can be done with
unix> epicbscalgen -V 5 eventtable=ev.ds 2>&1 | tee log
(sh syntax) which duplicates the standard error and output stream
and logs all output in the file log. While the task is running
the convergence process can then be monitored by periodically checking
the content of log for the actual values of and
unix> fgrep 'Iteration' log
unix> fgrep 'New set of Euler angles' log
With each iteration, should get smaller and the Euler angle
tuple should approach the sought solution.
- In the very first iteration, the user is required to input the
true coordinates of at least two sources interactively. For this
Ds9 is launched showing an image that has been
accumulated from the input event list with all found sources marked
through excluded circles. For each source that is to be used
as a reference source the user needs to:
- Double click with the left mouse button on the respective circle
- In the dialog box that will pop up:
- Select the menu item ``Properties''
After that the circle marker will be redrawn with a solid line which marks
the source as a reference source.
- In the field ``Text'', input the celestial J2000 coordinates
(right ascension/declination) of the source in the form
23h59m48.12s / 45o38'14.55"
123.23445 / 45.238474
- Click on ``Apply'' and ``Close''
If done, hit the Enter key in the terminal window from which
the task was started. If all input is ok, execution shall proceed normally,
otherwise an error message should be produced.
There is an alternative reference source input method available that
is activated with the withrefsrclist parameter. Here an
eboxdetect-compliant source list data set is required
from which the true celestial coordinates will be obtained. As in the
scheme described above in a first iteration a source detection will
be performed on the image from the given event list and the result
displayed using Ds9. Then, the given reference source list is
read and likewise displayed on the image however with a different
color and the markers labeled with the respective source indices.
The user is now requested to perform the cross-correlation between
the two source marker sets by activating, i.e. including, the
corresponding markers from the source detection run and labeling them
with the right indices. Detailed on-screen instructions on this
are given when this input scheme is selected.
- Convergence to the minimum can be slow - in this
regard it is worth noticing that the Nelder-Mead-Simplex method is
not optimized for minimum number of function evaluations. Please monitor
the convergence process in the above described manner. As long as
is steadily decreasing there is no need for any intervention.
- If two or more of the selected reference sources do not differ in flux
by more than 5% it is conceivable that possible source-confusion problems
are reported. This is not a real problem as long as the affected sources
are sufficiently spatially separated from each other such that the
scheme can uniquely identify them in each iteration. A failure to do
so would typically lead to an oscillating . In this case, please
stop the task and re-start with different reference sources. Choosing a
different source radius (see parameter sourceradius)
may also help to resolve the problem.
- The above described scheme is rather CPU intensive because it
involves the execution of several non-trivial tasks. The main performance
driver is clearly the size of the initial event list which should be kept
as small as possible.
XMM-Newton SOC/SSC -- 2006-06-28