Notes on analyzing XMM-Newton data using XSELECT

See also the section in the XMM ABC guide.

Preparatory steps

Before reading an XMM-Newton EPIC event file into XSELECT it is a good idea do a preliminary screening in PATTERN, PI, and FLAG to remove bad events. While this can be done using the select events command inside XSELECT this will not set all the keywords required by subsequent SAS commands. Instead use this xmmclean perl script (note that you will probably have to edit the first line to point to your local copy of perl). eg
mv P0125960201M2S010MIEVLI0000.FTZ P0125960201M2S010MIEVLI0000.fits.gz
gunzip P0125960201M2S010MIEVLI0000.fits.gz
xmmclean P0125960201M2S010MIEVLI0000.fits.gz mos1-clean.fits

Reading the data into XSELECT

[murasaki:~/XMM/0125960201] kaa% xselect
 
                         **  XSELECT V2.2   **
 
> Enter session name >[xsel] 
 
 Notes: XSELECT set up for      ASCA
 Time keyword is TIME       in units of s
 Default timing binsize =   16.000
 
xsel:ASCA > read e             
> Enter the Event file dir >[./] 
> Enter Event file list >[ ] mos1-clean.fits
Got new mission: XMM
> Reset the mission ? >[yes] 
 
 Notes: XSELECT set up for      XMM
 Time keyword is TIME       in units of s
 Default timing binsize =   16.000
 
 
Setting...
 Image  keywords   = X          Y           with binning =   32
 WMAP   keywords   = DETX       DETY        with binning =   64
 Energy keyword   = PI                     with binning =    1
 
Getting Min and Max for Energy Column...
Got min and max for PI:     0  15000
 
Could not get minimum time resolution of the data read
 Number of files read in:  1
 
******************** Observation Catalogue ********************
 
Data Directory is: /Users/kaa/XMM/0125960201/
HK Directory is: /Users/kaa/XMM/0125960201/
 
 
        OBJECT      OBS_ID      DATE-OBS    DATAMODE    FILTER
      1 NGC253      0125960201  2000-06-04T IMAGING     Medium

Making an image

XSELECT sets a default binning on images of 32 which should be appropriate. You can override this by using set xybin but should note that using too small a binning will produce very large images. 
xsel:XMM-EMOS1-IMAGING > extract image
extractor v4.20      1 Nov 2002
 Getting FITS WCS Keywords
 Doing file: /Users/kaa/XMM/0125960201/mos1-clean.fits
100% completed
          Total      Good    Bad: Region      Time     Phase       Cut
          97216     97216              0         0         0         0
===============================================================================
   Grand Total      Good   Bad:  Region      Time     Phase       Cut
         97216     97216              0         0         0         0
   in  13587.     seconds
 Image            has    97216 counts for  7.155     counts/sec
xsel:XMM-EMOS1-IMAGING > plot image
This will display the current image using ds9. It can be saved to a FITS file by : 
xsel:XMM-EMOS1-IMAGING > save image mos1-clean.img
Wrote image to file mos1-clean.img

Removing bad time intervals

Since XMM-Newton EPIC data can suffer from flaring background it is a good idea to look at the light curve and excise bad time intervals. To make a light curve in XSELECT... 
xsel:XMM-EMOS1-IMAGING > extr curve
extractor v4.20      1 Nov 2002
 Getting FITS WCS Keywords
 Doing file: /Users/kaa/XMM/0125960201/mos1-clean.fits
100% completed
          Total      Good    Bad: Region      Time     Phase       Cut
          97216     97216              0         0         0         0
===============================================================================
   Grand Total      Good   Bad:  Region      Time     Phase       Cut
         97216     97216              0         0         0         0
   in  13587.     seconds
 Fits light curve has    97216 counts for  7.155     counts/sec
This makes a light curve with 16 second bins. You can change this binning using set binsize. To look at the light curve... 
xsel:XMM-EMOS1-IMAGING > plot curve
and to filter out bad time intervals by clicking on appropriate positions on the plot... 
xsel:XMM-EMOS1-IMAGING > filter time cursor
and follow the instructions printed on your screen. Note that you can also excise all times with a count rate above some critical value using filter intensity.

Extracting a spectrum

To extract spectra from part of the image you need to create a region filter file. This can be done using ds9 (use the ds9/funtools file format and equatorial J2000 coordinate system). Here is an example I made earlier... 
xsel:XMM-EMOS1-IMAGING > $cat ds9.reg
 Spawning...
# Region file format: DS9 version 3.0
global color=green font="helvetica 10 normal" select=1 edit=1 move=1
 delete=1 include=1 fixed=0 source
fk5;circle(11.888759,-25.292201,52.800001")
To use this to extract a spectrum... 
xsel:XMM-EMOS1-IMAGING > filter reg ds9.reg
xsel:XMM-EMOS1-IMAGING > extr spec
extractor v4.20      1 Nov 2002
 No wmap X-axis TCRVL, set to 0
 No wmap Y-axis TCRVL, set to 0
 Doing file: /Users/kaa/XMM/0125960201/mos1-clean.fits
100% completed
          Total      Good    Bad: Region      Time     Phase       Cut
          97216      7007          90209         0         0         0
===============================================================================
   Grand Total      Good   Bad:  Region      Time     Phase       Cut
         97216      7007          90209         0         0         0
   in  13554.     seconds
 Spectrum         has     7007 counts for 0.5170     counts/sec
 ... written the PHA data Extension
This spectrum can then be saved using save spectrum. You should answer yes to the question about grouping (or rebinning) since this will make a standard size spectrum.

Automated response generation

The save spec resp=yes option for XMM-Newton EPIC data runs the perl script xsl_xmm_epic_makeresp which calls the SAS routines rmfgen and arfgen. The arfgen call assumes a point source and does not correct for bad pixels and attitude variations (both of which should have a very small effect). To use the arfgen extended source option set resp=extend.

A service of the Laboratory for High Energy Astrophysics (LHEA) at NASA's GSFC
Responsible NASA Official: Phil Newman
Curator: Keith Arnaud

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This file was last modified on Wednesday, 14-Mar-2012 17:45:45 EDT