XMM-Newton EPIC Background Analysis
Introduction to Background Analysis Scripts
The scripts below have been developed to perform various aspects of background
analysis and subtraction of XMM-Newton data, and are especially useful
for the analysis of extended objects. They make extensive use of the XMM-SAS
tasks, and HEASOFT's FTOOLS utilities. Though a number of the scripts may
simply combine several SAS analysis steps together, it is advisable to
read through a script before using it, to be clear on exactly what it does.
While they have been written with generality in mind, there may be assumptions,
or default values within them which are not what is required. The scripts
were initially developed for use with SAS-5.2, but have been updated and
configured to work with SAS-5.3. They have been developed using solaris
and Linux, and have been tested, though errors may still remain, and should
be reported to Andy Read
at Birmingham.
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EPIC background datasets have been produced by Dave Lumb by co-adding
several source-subtracted datasets. These `blank sky' event lists can
be used within the scripts presented here. They can be obtained from
here,
along with useful explanatory
notes. More recent, long-exposure EPIC background maps and
datasets have been produced by Andy Read. These products, together
with related software and explanotary notes, can be obtained here.
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Furthermore, event lists combining several CLOSED observations have been
created by Phillipe Marty, and these have also proven very useful in the
analysis and background-subtraction of extended objects. A zipped tarball
containing MOS1, MOS2 and PN (full-frame and extended full-frame) CLOSED
data is available here.
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A very brief summary outlining current thinking as to the temporal, spatial
and spectral properties of the major components contributing to the XMM-Newton
background can be found here.
There are a couple of useful points to note when using the following
scripts:
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To see the full task help and the input arguments required by a script,
type the script name on the command line with no arguments
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It is always a good idea to 'pipe' the output of a script to a log file,
using e.g. tee. For example:
script.csh argument1 argument2 root |& tee rootlog.txt
This means you have a record of what the script did, and the arguments
you gave it.
To download an individual script, shift-click on its name in the list below.
A zipped tarball containing all of the background analysis scripts is
available here.
The scripts are written in TCSH shell, and should run on solaris or
linux machines.
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Description of Individual Background Analysis
Scripts
Brief descriptions of the background analysis scripts are given here. More
extensive help is obtained by just typing the script name on the command
line.
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skycast
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Casts XMM EPIC background datasets (or indeed any EPIC event dataset) onto
the sky, at the position given by an input template event dataset or image.
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imageBGsub
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Performs rigorous background subtraction of an image, using blank sky
background fields and filter-CLOSED observations.
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compareoutofFOV
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Compares counts in the out-of-field-of-view regions of two event files
(e.g. a source and blank-sky background file). Useful for background scaling.
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createspectra
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Creates spectra in specific annuli from two event files (e.g. source and
background spectra). A scaling factor (from e.g. compareoutofFOV) is applied,
and scaled background and source minus scaled background (`soft excess')
spectra are produced. Arf and rmf files are also produced.
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doublesubtraction
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Given source and scaled background spectra from the same area (e.g. from
createspectra) and a large-radius `source minus scaled background' spectrum
(e.g. from createspectra), a `double-background' spectrum is created, associated
with the source spectrum (along with arf and rmf files) and grouped together
as input to xspec.
Before running any of these scripts, the XMM-SAS needs to be
correctly configured, and all relevant SAS environment variables
(e.g. SAS_ODF, SAS_CCF) need to be correctly set.
To create a background subtracted image, the relevant blank-sky
background and filter-CLOSED datsets need to be skycasted. Also, the
same filtering (for flares, pattern etc.) performed on the user's
source dataset should be performed on the blank-sky background
dataset. Once this is done, imageBGsub can be
run.
To create XSPEC-compatible source and background spectra, the relevant
blank-sky background dataset needs to be filtered to the same
degree as the user's source dataset. A scaling value, obtained via
e.g. compareoutofFOV,
can then be fed into createspectra,
firstly far from any source region, to create a large-radius `soft
excess' spectrum. Annular source and blank-sky background spectra can
then be created from the source regions via successive small-radius
runs of createspectra. Finally,
doublesubtraction
creates a `double-background', comprising of the source background and
the correctly area-scaled `soft excess' background, and associates
this with a XSPEC-compatible source spectrum.
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Further pages on XMM-Newton Data Analysis at Birmingham can be found
here.
Mail to Andy Read - University of Birmingham
Andy Read - Home page
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