Reprocessing of ODFs to generate EPIC concatenated and
calibrated event list
This thread illustrates you how to reprocess Observation Data Files
(ODF) to obtain calibrated and concatenated event lists, which
can be directly used to generated scientific products
(images, spectra, light curves) through
evselect
or xmmselect.
How to reduce EPIC ODFs
-
set up your SAS environment (following the
SAS
start-up thread)
- run the EPIC reduction meta-tasks. For the MOS:
emproc
For the pn:
epproc
That's it! The default values of these meta-tasks are appropriate for
most practical cases.
You may have a look at the next section
to learn how to perform specific reduction sub-tasks using
emproc
or epproc.
The files produced by
epproc
are the following:
- ????_??????????_AttHk.ds, the reconstructed attitude file
- ????_??????????_EPN_????_01_Badpixels.ds, one table
per reduced CCD containing
the bad pixels
- ????_??????????_EPN_????_ImagingEvts.ds, the calibrated
and concatenated event list, which shall be used as an input to extract
scientific products via
evselect
or xmmselect.
The files produced by
emproc
are conceptually the same. The main difference in the naming convention
is that the string EPN is replaced by EMOS1 and
EMOS2 for each MOS camera, respectively.
How to accomplish specific reduction tasks
emproc
and epproc
are highly flexible tasks, which allow the user to perform
a wide range of customized reduction tasks.
Some emproc
examples are listed below. The same customized reduction tasks can be
performed for the pn as well, just by substituting in these
commands
emproc
with epproc.
- if you want to reduce only one of the cameras (MOS1 in the
example):
emproc selectinstruments=yes emos1=yes
- if you want to reduce only a subsample of exposures:
emproc withinstexpids=yes instexpids="M1S001 M2S002"
- if you want to reduce data from 1 CCD only (#4 and #5 in the example):
emproc selectccds=yes ccd4=yes ccd5=yes
- if you want to change the reference pointing for the calculation
of the sky coordinates to a value of your choice:
emproc referencepointing=user ra=34.65646 dec=-12.876546
- if you want to filter the event list events, using an external
Good Time Interval (GTI) file:
emproc withgtiset=yes gtiset=mygti.gti filterevents=yes
Please, be aware
that if you want to supply coordinates for the analysis of Timing
and Burst pn mode, the command is slightly different:
epproc withsrccoords=yes srcra=34.65646 srcdec=-12.876546
Parameters can be combined to accomplish simultaneously
two or more of the above tasks during the same run.
The user is referred to the on-line documentation of
emproc
and epproc
for a complete list of the available options.
Should I indeed bother to regenerate my event lists?
Concatenated and calibrated EPIC event lists are already available
in the PPS Pipeline Products. These are produced with the most updated software
and calibrations available at the moment the observation was performed
and - normally a couple of weeks later - the ODF are produced. There
is therefore no need for you to regenerate the EPIC event lists
yourself, unless substantial changes in the software and/or calibration
occurred between the time when
Pipeline Products were generated
and the
moment you are analyzing the data. Of course, there is no general
answer or recipe one can apply to decide if/when this is the case.
In order to collect all the available and necessary
elements to formulate your judgment, follow these steps:
- check in the
XMM-Newton Science Archive the
SAS version and the date when the
Calibration Index File was generated to produce the
Pipeline Products
(a primary introduction to the usage of
the science archive is available
here)
- verify in the SAS release notes the software changes between the version
employed to produce the
Pipeline Products
and the
latest SAS version
- verify in the CCF release notes the changes in the calibration
files between the moment when
Pipeline Products
were generated and
the moment your analysis is being performed
If your feel lost or unsure, and prefer to stay on the safe side,
you'd probably better regenerate your EPIC calibrated event lists.