National Aeronautics and Space Administration

EXOSAT Software Page

The EXOSAT raw data FITS files (currently available for the LE instrument) include Catalog, Orbit, Photon Events and Housekeeping data. These files can be used to create images and lightcurves from the LE data. Software has been written to select and merge photon event files and correct the data for deadtime. The information below illustrates the use of the EXOSAT programs, tkexomerge and cmadead as well as the multi-mission package, Xselect in creating a lightcurve and performing deadtime corrections.

1. Merging event files
2. Xselect & region filtering
3. Correcting for Deadtime

EXOSAT- Making a Lightcurve: 1. Merging event files

• Tkexomerge provides a short summary of the catalog listing of all associated event files. It also provides a means of selecting which event files to merge.

• The output from tkexomerge is then sent to exomerge which checks that the star tracking mode, the detector, the filter, on board computer mode and grating setting are the same for all of the event files before merging. Exomerge will also correct the reference coordinates in the cases where EXOSAT was operating in a star tracking 1 mode (i.e. using 1 guide star and the Fine Sun Sensor).

EXOSAT- Making a Lightcurve: 2. Xselect & region filtering

Running Xselect on the merged event file

Through Xselect you may select a region within the field from which to extract a lightcurve (via SAOImage). Xselect will also allow you to set the binning size for the image and the lightcurve, and the minimum exposure. You may then view the lightcurve (via PGPLOT). Below is a sample run of Xselect using the merged event file.

xselect
 
                         **  XSELECT V1.4b  **
 
> 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 events
> Enter the Event file dir >[./] 
> Enter Event file list >[] ex830630_0316_1320_cma1_3lx.fits
Got new mission: EXOSAT
> Reset the mission ? >[yes] 
 
 Notes: XSELECT set up for      EXOSAT
 Time keyword is TIME       in units of s
 Default timing binsize =   16.000
 
 
Setting...
 Image  keywords   = X          Y           with binning =    4
 WMAP   keywords   = X          Y           with binning =    4
 Energy keywords   = PHA                    with binning =    1
 
 
Getting Min and Max for Energy Column...
Got min and max for PHA:     0    127
 
Could not get minimum time resolution of the data read
Number of files read in:            1
 
******************** Observation Catalogue ********************
 
Data Directory is: /Usr1/processing/develop/data/
HK Directory is: /Usr1/processing/develop/data/
 
 
        OBJECT     DATE-OBS   TIME-OBS
      1 AM HER     30/06/83   03:16:18
 
xsel:EXOSAT-CMA1 > set xybinsize
> Rebinning factor for the image >[8] 1
xsel:EXOSAT-CMA1 > extract image
extractor v3.47  2 Mar 1999
 Getting FITS WCS Keywords
 Doing file: /Usr1/processing/develop/data/ex830630_0316_1320_cma1_3lx.fits
100% completed
          Total      Good    Bad: Region      Time     Phase       Cut
         718690    718468              0       222         0         0
===============================================================================
   Grand Total      Good   Bad:  Region      Time     Phase       Cut
        718690    718468              0       222         0         0
   in   36259.00 seconds
 Image            has   718468 counts for  19.81     counts/sec
xsel:EXOSAT-CMA1 > sao

xsel:EXOSAT-CMA1 > filter region saoimage.reg
xsel:EXOSAT-CMA1 > extract curve exposure=0.0
extractor v3.47  2 Mar 1999
 Doing file: /Usr1/processing/develop/data/ex830630_0316_1320_cma1_3lx.fits
100% completed
          Total      Good    Bad: Region      Time     Phase       Cut
         718690     59148         659541         1         0         0
===============================================================================
   Grand Total      Good   Bad:  Region      Time     Phase       Cut
        718690     59148         659541         1         0         0
   in   36259.00 seconds
 Fits light curve has    59148 counts for  1.631     counts/sec
xsel:EXOSAT-CMA1 > plot curve

> Which plotting device? >[NONE] XW
 Plotting device chosen: /XW
 
Note: cursor timing selection is now done with the command
   FILTER TIME CURSOR
 
PLT> hardcopy
PLT> exit
xsel:EXOSAT-CMA1 > save curve
> Give output file name >[] amher.lc
Wrote FITS light curve to file amher.lc
xsel:EXOSAT-CMA1 > exit
> Save this session? >[no] yes
Session saved, goodbye

EXOSAT- Making a Lightcurve: 3. Correcting for Deadtime

Correcting for deadtime using cmadead on the lightcurve

Lightcurves from the EXOSAT LE instrument need to be corrected for deadtime due to the electronics and to the telemetry. Cmadead corrects the lightcurve FITS file using the OBC_PACKET extension within the event files. The program requires the lightcurve filename and the event filename or a file containing the event filenames.

The corrected FITS lightcurve can then be viewed using programs such as lcurve.

cmadead
Name of input file[amher.lc] 
Name of event file[@evtlist] 
Name of output file[hh2_mrg] amher_cor.lc
Processing a lightcurve
Reading ex830630_0316_1320_cma1_3lx.fits
Computing deadtime corrections
Writing 2237 rows