At present, if a source is producing (or expected to produce) < 40 counts/s, it is safe to assume no pile-up for the PC mode. This limiting count rate will be ~8.6 times larger in the FW mode. Our current analysis shows that in order to get rid of pile-up for ultra-bright sources like Crab, Cyg X-1 etc., a 1 arcmin central removal of the PSF is enough.
$ xselect
** XSELECT V2.4j **
$ Enter session name >[ ] xsel
$ xsel:NICER > read event AS1A02_090T01_9000000778sxtPC00_level2_cl.evt
$ Enter the Event file dir >[ ]
/path/to/data_directory/20161108_A02_090T01_9000000778_level2_06029_V1.1/sxt/06029/sxt.02
Got new mission: ASTROSAT
Here /path/to/data_directory/ is the path where you have saved your SXT data.
$ 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/data_directory/20161108_A02_090T01_9000000778_level2_06029_V1.1/sxt/06029/sxt.02/
HK Directory is:
/path/to/data_directory/20161108_A02_090T01_9000000778_level2_06029_V1.1/sxt/06029/sxt.02/
TELESCOP INSTRUME DATAMODE DATE-OBS OBJECT ORB_NUM
1 ASTROSAT SXT PC 2016-11-08 Crab 6029
$ xsel:ASTROSAT-SXT-PC > filter region ds9.reg
$ xsel:ASTROSAT-SXT-PC > extract curve
extractor v5.36 26 Feb 2020
Getting FITS WCS Keywords
Doing file: /path/to/data_directory/20161108_A02_090T01_9000000778_level2_06029_V1.1/sxt/06029/sxt.02/AS1A02_090T01_9000000778sxtPC00_level2_cl.evt[regfilter("xsel_region.xsl",X,Y)]
100% completed
Total Good Bad: Time Phase Grade Cut
7097 7097 0 0 0 0
===============================================================================
Grand Total Good Bad: Time Phase Grade Cut
7097 7097 0 0 0 0
in 109.36 seconds
Fits light curve has 7097 counts for 64.89 counts/sec
This count rate is above the limit for pile-up. Thus, the next step is to extract an image taking an annular region of inner radii 4.5 arcminutes and outer radii 12 arcminutes.
$ xsel:ASTROSAT-SXT-PC > plot curve
$ xsel:ASTROSAT-SXT-PC > filter region annulus.reg
$ xsel:ASTROSAT-SXT-PC > extract curve
extractor v5.36 26 Feb 2020
Getting FITS WCS Keywords
Doing file: /path/to/data_directory/20161108_A02_090T01_9000000778_level2_06029_V1.1/sxt/06029/sxt.02/AS1A02_090T01_9000000778sxtPC00_level2_cl.evt[regfilter("xsel_region.xsl",X,Y)]
100% completed
Total Good Bad: Time Phase Grade Cut
3980 3980 0 0 0 0
===============================================================================
Grand Total Good Bad: Time Phase Grade Cut
3980 3980 0 0 0 0
in 109.36 seconds
Fits light curve has 3980 counts for 36.39 counts/sec
This count rate is now below the limit for pile-up.
$ xsel:ASTROSAT-SXT-PC > plot curve
$ PLT> hardcopy crab_lightcurve.ps/cps
$ PLT> exit
$ xsel:ASTROSAT-SXT-PC > extract all
extractor v5.36 26 Feb 2020
Getting FITS WCS Keywords
Doing file: /path/to/data_directory/20161108_A02_090T01_9000000778_level2_06029_V1.1/sxt/06029/sxt.02/AS1A02_090T01_9000000778sxtPC00_level2_cl.evt[regfilter("xsel_region.xsl",X,Y)]
100% completed
Total Good Bad: Time Phase Grade Cut
3980 3980 0 0 0 0
===============================================================================
Grand Total Good Bad: Time Phase Grade Cut
3980 3980 0 0 0 0
in 109.36 seconds
Fits light curve has 3980 counts for 36.39 counts/sec
Spectrum has 3980 counts for 36.39 counts/sec
... written the PHA data Extension
Image has 3980 counts for 36.39 counts/sec
$ xsel:ASTROSAT-SXT-PC > save all crab
Saving the Spectrum:
Wrote spectrum to crab.pha
Saving the Image:
Wrote image to file crab.img
Saving the Light Curve:
Wrote FITS light curve to file crab.lc
$ xsel:ASTROSAT-SXT-PC > exit
$ Save this session? >[ ] No