Chandrayaan-2 XSM
Solar X-ray Monitor
Chandrayaan-2 XSM
Solar X-ray Monitor
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XSM Instrument
Observations with XSM
Data Analysis
Publications
Gallery CH-2 Data Archive

Accessing XSM Data

This website provides only the plots of solar X-ray flux integrated over either the GOES XRS-B energy range (1-8 Å or 1.55 to 12.4 keV) or the full XSM energy range (1 - 15 keV), obtained from the XSM spectra. Full spectral data is available in the data archive. The raw (level-1) and calibrated (level-2) XSM data organized into day-wise files are available for download from the PRADAN portal of ISRO Science Data Archive (ISDA) at Indian Space Science Data Center (ISSDC), Bangalore.

To dowload the data, visit https://pradan.issdc.gov.in/ch2/. Users need to register in the website for accessing the data.

Analysis Guide, Software, and Calibration Files

XSPEC Model and fitting example

Acknowledging the use of XSM data

Users are requested to acknowledge the use of XSM data and analysis software by citing the relevant publications listed below as well as by including the following statement in acknowledgment:
"We acknowledge the use of data from the Solar X-ray Monitor (XSM) on board the Chandrayaan-2 mission of the Indian Space Research Organisation (ISRO), archived at the Indian Space Science Data Centre (ISSDC). XSM was developed by Physical Research Laboratory (PRL) with support from various ISRO centers."

References

  1. Instrument description: "Solar X-ray Monitor Onboard Chandrayaan-2 Orbiter", Current Science, 118(1):45, 2020. [ArXiv] [ADS]
  2. In-flight calibration status: "Solar X-ray Monitor On board the Chandrayaan-2 Orbiter: In-flight Performance and Science Prospects", Solar Physics , 295:139, 2020. [ArXiv] [ADS]
  3. Software description: "Data Processing Software for Chandrayaan-2 Solar X-ray Monitor", Astronomy & Computing, 34:100449, 2021. [ArXiv] [ADS]
  4. Ground calibration: "Ground Calibration of Solar X-ray Monitor on board the Chandrayaan-2 Orbiter", Experimental Astronomy, 51:1, 2021. [ArXiv] [ADS]

XSM Data Analysis: A Quick Start Guide

This guide assumes that the users have successfully installed XSMDAS and CALDB and have XSPEC/Heasoft or OSPEX/Solarsoft available on their system for further analysis of the spectra. XSM observations on 17-September-2019 is considered as an example here, which includes a sub-A-class flare as seen from light curve plot generated from this website shown below. We will carry out spectroscopic analysis around the peak of this flare at 19:43:30.


Download the data for this day of observation from PRADAN and unzip the file into desired location. In this example, it is unzipped in to the directory ~/xsm_analysis as:

mithun@Thinkpad:xsm_analysis$ unzip ch2_xsm_20190917_v1.zip   

This will create a directory structure with xsm as top level directory with year, month, day level sub-directory structure under data as:

xsm/
   data/
       2019/
           09/
             17/
              raw/
                 ch2_xsm_20190917_v1_level1.fits
                 ch2_xsm_20190917_v1_level1.hk
                 ch2_xsm_20190917_v1_level1.sa
              calibrated/
                 ch2_xsm_20190917_v1_level2.gti
                 ch2_xsm_20190917_v1_level2.pha
                 ch2_xsm_20190917_v1_level2.lc
Now, to determine the time ranges for further analysis, examine the standard light curve available in the downloaded data set using fitsviewer or with python/IDL etc. Another possibility is to use the interactive plotting tool available on this web site. Convert the UTC time stamps to XSM Mission Elapse Time (MET) using xsmutc2met tool included in XSMDAS. We will use the following time ranges as the flare duration and non-flaring (post-flare) duration for the subsequent analysis.
Period Tstart Tstop
Flare 85520490.0 (19:41:30) 85520850.0 (19:47:30)
Non-flaring 85527600.0 (20:40:00) 85534800.0 (23:40:00)

Now, the spectral analysis procedure is demonstrated below using XSPEC and OSPEX.

Analysis Using XSPEC/HEASOFT

For analysis in XSPEC we shall generate spectra for the flare and non-flaring duration separately using the XSMDAS module xsmgenspec. To generate spectrum for the flare duration, provide inputs to xsmgenspec as shown below with the tstart and tstop values as identified above.


mithun@Thinkpad:~/xsm_analysis/xsm/data/2019/09/17/calibrated$ xsmgenspec
-------------------------------------------------------------------------
  XSMDAS: Data Analysis Software for Chandrayaan-II Solar X-ray Monitor
                     XSMDAS Version: 1.1
                     Module : XSMGENSPEC
-------------------------------------------------------------------------
Enter Input Level-1 file [] : ../raw/ch2_xsm_20190917_v1_level1.fits
Enter Output Spectrum file [] : ch2_xsm_20190917_flare.pha
Enter output spectrum type  [time-resolved] : time-integrated
Enter start time for extracting spectrum [0] : 85520490.0
Enter stop time for extracting spectrum [0] : 85520850.0
Enter HK file [] : ../raw/ch2_xsm_20190917_v1_level1.hk
Enter Sun angle file [] : ../raw/ch2_xsm_20190917_v1_level1.sa
Enter GTI file [] : ch2_xsm_20190917_v1_level2.gti
------------------------------------------------------------------------
MESSAGE: Ebounds CALDB file used is: /home/mithun/work/ch2/xsm/pipeline/XSM/xsmdas/caldb/CH2xsmebounds20191214v01.fits
MESSAGE: Gain CALDB file used is: /home/mithun/work/ch2/xsm/pipeline/XSM/xsmdas/caldb/CH2xsmgain20200330v03.fits
MESSAGE: Abscoef CALDB file used is: /home/mithun/work/ch2/xsm/pipeline/XSM/xsmdas/caldb/CH2xsmabscoef20200410v01.fits
MESSAGE: Effareapar CALDB file used is: /home/mithun/work/ch2/xsm/pipeline/XSM/xsmdas/caldb/CH2xsmeffareapar20200410v01.fits
MESSAGE: Syserror CALDB file used is: /home/mithun/work/ch2/xsm/pipeline/XSM/xsmdas/caldb/CH2xsmsyserr20200410v01.fits

MESSAGE: XSMGENSPEC completed successully
MESSAGE: Output file = ch2_xsm_20190917_flare.pha
MESSAGE: Output ARF = ch2_xsm_20190917_flare.arf

At the end of execution a spectrum file and arf file will be generated. Similarly generate spectrum and arf for the non-flaring duration by providing appropriate start and stop times. Before proceeding to detailed spectral analysis, load both these spectra in XSPEC with a sample background file provided under $xsmdas/caldb/bkgspec as the background spectra (either copy the background pha to present working directory or give full path) using appropriate XSPEC commands as below:

XSPEC12>da 1:1 ch2_xsm_20190917_flare.pha 

1 spectrum  in use
 
Spectral Data File: ch2_xsm_20190917_flare.pha  Spectrum 1
Net count rate (cts/s) for Spectrum:1  1.438e+01 +/- 2.307e-01
 Assigned to Data Group 1 and Plot Group 1
  Noticed Channels:  1-512
  Telescope: CH-2_ORBITER Instrument: CH2_XSM  Channel Type: PI
  Exposure Time: 360 sec
 Using fit statistic: chi
 Using test statistic: chi
 Using Response (RMF) File    /home/mithun/work/ch2/xsm/pipeline/XSM/xsmdas/caldb
/CH2xsmresponse20200423v01.rmf for Source 1
 Using Auxiliary Response (ARF) File  ch2_xsm_20190917_flare.arf

XSPEC12>back 1 ch2_xsm_20191128_bkg.pha
Net count rate (cts/s) for Spectrum:1  1.324e+01 +/- 2.307e-01 (92.1 % total)
XSPEC12>da 2:2 ch2_xsm_20190917_post-flare.pha

2 spectra  in use
 
Spectral Data File: ch2_xsm_20190917_post-flare.pha  Spectrum 2
Net count rate (cts/s) for Spectrum:2  7.242e+00 +/- 7.831e-02
 Assigned to Data Group 2 and Plot Group 2
  Noticed Channels:  1-512
  Telescope: CH-2_ORBITER Instrument: CH2_XSM  Channel Type: PI
  Exposure Time: 7200 sec
 Using fit statistic: chi
 Using test statistic: chi
 Using Response (RMF) File    /home/mithun/work/ch2/xsm/pipeline/XSM/xsmdas/caldb
/CH2xsmresponse20200423v01.rmf for Source 1
 Using Auxiliary Response (ARF) File  ch2_xsm_20190917_post-flare.arf

XSPEC12>back 2 ch2_xsm_20191128_bkg.pha
Net count rate (cts/s) for Spectrum:2  6.100e+00 +/- 7.840e-02 (84.2 % total)

Plot the spectra after ignoring the data below 1 keV and above 5 keV using ignore, plot, and setplot commands in XSPEC (see XSPEC manual). Figure below shows the resulting plot. The black data points denote the flare spectrum, red data points correpond to non-flaring period spectrum and the stars denote the background spectra.

As noted in caveats below, background in XSM shows slight variability and thus it is recommended to restrict the spectral analysis to energies where the source is well above background. In this example, we shall choose non-flaring spectrum up to 2.3 keV and flare spectrum up to 2.7 keV for spectral fitting. We also need to ignore the spectra below 1.3 keV as noted in the caveats (this observation is before June 2020).

First, we fit the pre-flare spectrum with an isothermal plasma emission model vapec. The abundances shall be set to typical solar coronal abundances and that of elements Mg, Al, and Si shall be left free while fitting. Refer to XSPEC manual for the steps involved. We then fit the flare spectrum by using a two temperature model, as the sum of two vapec models. The parameters of the first component is frozen to that obtained for pre-flare duration whereas the parameters of the second component are left free. Flare spectrum with the best fit two-component model is shown in the below figure for reference.

Analysis Using OSPEX/SSW

To load the XSM spectral data (level-2 time-series PHA file) and response in OSPEX, two IDL routines are provided along with the XSMDAS distribution (see the directory $xsmdas/idl). Add this location to IDL PATH or copy the two IDL rouines named ch2xsm_read_data.pro and ch2xsm_read_drm.pro to any of the pre-defined IDL PATH locations, so that they are accessible by SolarSoft. It may be noted that these routines are not meant to be used independant of OSPEX.

For XSM data analysis with OSPEX, start SSW IDL session and invoke OSPEX as:


o=ospex()

This will open up a window of OSPEX GUI. Then, set the spex file reader to the XSM data read routines as:


o->set, spex_file_reader='ch2xsm_read'

Then, use File -> Select Input option in the GUI to load the standard time-resolved spectrum file (60 s cadence) available under the calibrated directory into OSPEX. After loading the file, on clicking plot time profile option, OSPEX window will plot the light curves in different energy bands as shown below.

For analysis of flare spectrum, we need to select a flare time interval and a non-flaring time interval (as background) using the select time interval options in the OSPEX window. An example of flare and background time selection is shown below.

After the selection, on plotting the spectrum for the selected flare duration, window will show the spectrum as below where the fitting interval is selected as 1.3-3.0 keV.

Now, one can proceed to fit the spectrum with available models in OSPEX, suitable one being vth_abun.


Caveats and Notes to Users


XSMDAS and CALDB Release Notes


Release history of XSM Data Analysis Softwarre (XSMDAS) and Calibration Database (CALDB) are given here.

XSMDAS Release History

Version Release Date Notes
1.1 10 Dec 2020 First public release
1.2 28 Jun 2021 Included python script for computing flux over a user provided energy range; CALDB version used are written in output spectra/resp/lc headers.

CALDB Release History

Version Release Date Notes
20201210 10 Dec 2020 First public release
20210628 28 Jun 2021 Added new gain file for observations from June 2020 with new LLD setting and updated effective area parameters for N-M season