Here we demonstrate how to extract source and background light curves from SXT Level 2 data using XSELECT. The PC mode 28th March 2017 observation of GRS 1915+105 is used for an example. The observation id is G06_033T01_9000001116. The test data used here is available in the public domain and can be downloaded from the astrobrowser portal.
Go to the ‘Results’ folder where you want to extract your results.
$ cd Results
$ xselect
** XSELECT V2.4j **
$ Enter session name >[ ] xsel
$ xsel:NICER > read event GRS_1915_sxt_merged_cl.evt
$ Enter the Event file dir >[ ] ./
Got new mission: ASTROSAT
$ Reset the mission ? >[ ] yes
Notes: XSELECT set up for ASTROSAT
Time keyword is TIME in units of s
Default timing binsize = 5.0000
Setting...
Image keywords = X Y with binning = 1
WMAP keywords = X Y with binning = 1
Energy keyword = PI with binning = 1
Getting Min and Max for Energy Column...
Got min and max for PI: 0 1023
Got the minimum time resolution of the read data: 2.3775
MJDREF = 5.5197000000000E+04 with TIMESYS = UTC
Number of files read in: 1
******************** Observation Catalogue ********************
Data Directory is: /path_to_present_directory/
HK Directory is: /path_to_present_directory/
TELESCOP INSTRUME DATAMODE DATE-OBS OBJECT ORB_NUM
1 ASTROSAT SXT PC 2017-03-29 GRS 1915+105 8118
$ xsel:ASTROSAT-SXT-PC > filter region ds9.reg
$ xsel:ASTROSAT-SXT-PC > filter pha_cut 100 500
$ xsel:ASTROSAT-SXT-PC > show filters
*** SELECTIONS ***
NONE
*** FILTERS ***
A PHA filter from 100 to 500 has been entered
Spatial selections have been read in from:
ds9.reg
PHA Lower cutoff = 100 PHA Upper cutoff = 500
$ xsel:ASTROSAT-SXT-PC > extract curve
extractor v5.36 26 Feb 2020
Getting FITS WCS Keywords
Doing file: /path_to_present_directory/GRS_1915_sxt_merged_cl.evt[regfilter("xsel_region.xsl",X,Y)]
100% completed
Total Good Bad: Time Phase Grade Cut
138211 125708 0 0 0 12503
===============================================================================
Grand Total Good Bad: Time Phase Grade Cut
138211 125708 0 0 0 12503
in 5068.8 seconds
Fits light curve has 125708 counts for 24.80 counts/sec
Thresholding removed significant counts
Try exposure=0.0 on the extract command in xselect
or lcthresh=0.0 if running extractor stand-alone
Thresholding removed more than half the bins
Try exposure=0.0 on the extract command in xselect
or lcthresh=0.0 if running extractor stand-alone
$ xsel:ASTROSAT-SXT-PC > plot curve
$ PLT> hardcopy lightcurve_1_5_keV.ps/cps
$ PLT> exit
The light curve above is extracted for the 1.0 -5.0 keV energy range. However, the data can be filtered to produce images over any energy band. using the command filter pha_cutoff, where the range must be given in terms of channels. For the SXT, 1 channel = 100 eV.
$ xsel:ASTROSAT-SXT-PC > save curve lightcurve
$ xsel:ASTROSAT-SXT-PC > clear region
$ xsel:ASTROSAT-SXT-PC > extract image
Getting FITS WCS Keywords
Doing file: /path_to_present_directory/GRS_1915_sxt_merged_cl.evt
100% completed
Total Good Bad: Time Phase Grade Cut
166868 142584 0 0 0 24284
===============================================================================
Grand Total Good Bad: Time Phase Grade Cut
166868 142584 0 0 0 24284
in 5068.8 seconds
Image has 142584 counts for 28.13 counts/sec
$ xsel:ASTROSAT-SXT-PC > plot image
$ xsel:ASTROSAT-SXT-PC > filter region Bkg.reg
$ xsel:ASTROSAT-SXT-PC > show filters
*** SELECTIONS ***
NONE
*** FILTERS ***
A PHA filter from 100 to 500 has been entered
Spatial selections have been read in from:
Bkg.reg
PHA Lower cutoff = 100 PHA Upper cutoff = 500
$ xsel:ASTROSAT-SXT-PC > extract curve
Getting FITS WCS Keywords
Doing file: /path_to_present_directory/GRS_1915_sxt_merged_cl.evt[regfilter("xsel_region.xsl",X,Y)]
100% completed
Total Good Bad: Time Phase Grade Cut
291 255 0 0 0 36
===============================================================================
Grand Total Good Bad: Time Phase Grade Cut
291 255 0 0 0 36
in 5068.8 seconds
Fits light curve has 255 counts for 5.0308E-02 counts/sec
Thresholding removed significant counts
Try exposure=0.0 on the extract command in xselect
or lcthresh=0.0 if running extractor stand-alone
Thresholding removed more than half the bins
Try exposure=0.0 on the extract command in xselect
or lcthresh=0.0 if running extractor stand-alone
$ xsel:ASTROSAT-SXT-PC > plot curve
$ PLT > exit
$ xsel:ASTROSAT-SXT-PC > save curve Bkg_lightcurve
Wrote FITS light curve to file Bkg_lightcurve.lc
$ xsel:ASTROSAT-SXT-PC > exit
$ Save this session? >[ ] No