1. K.J. Shah Physical Research Laboratory (Unit of Dept. of Space, Govt. of India) Navrangpura, Ahmedabad – 380 009

2.  Indigenously designed and developed in Physical Research Laboratory (PRL), India  Launched onboard GSAT-2 Indian spacecraft by GSLV-D2 rocket on 08 May 2003.  The main objective of mission is to study X-ray emission from solar flares in 4-56 keV energy range.  SOXS has Silicon Pin (Si) detector for observation in the energy range of 4–25 keV and cadmium– zinc–telluride (CZT) detector for energy band of 4–56 keV. Introduction: SOLAR X-Ray Spectrometer (SOXS)

3. Data Flow: SOXS  Data Flow schematics from GSAT-2 to MCF-HASAN  Finally to PRL, the home data archive server( www.prl.res.in/~soxs-data ) www.prl.res.in/~soxs-data

4. SOXS Data Format  SOXS payload data from memory banks is online downloaded @ 8 kbps telemetry rate to Master Control Facility (MCF), Hasan, where data packaging is done at every 1248 bytes.  Data mainly contains 700 bytes of payload data and 212 bytes of deriverd and current Process Identification (PID) values.  SOXS payload data have 8 bytes Header Information which contains ID codes, data phases and On Board Time (OBT) as follows, AC CA 1FPhase On Board Time (OBT) 0 1 2 3 4 5 6 7 OBT= b(7) + b(6) * 256 + b(5) * 256 ^2 + b(4) * 256^3

5. Byte Detail For Various Phases  Search / Quiet Phase: 8 Bytes Header638 Bytes Spectral Data54 Bytes Temporal Data 8 Bytes Header638 Bytes Spectral Data 18 Bytes Temporal Data 36 Dummy  Flare Phase : Details of Spectral(PHA) 638 Bytes are as follows, Si – PIN - 96 Double Bytes = 192 Bytes Si – PIN - 160 Single Bytes = 160 Bytes CZT - 30 Double Bytes = 60 Bytes CZT - 226 Single Bytes = 226 Bytes Temporal(Counts) Data : Si – PIN - 4 Energy Windows Double Bytes ( 6-7 keV, 7-10 keV, 10-20 keV, 4-25 keV) CZT - 5 Energy Windows Double Bytes ( 6-7 keV, 7-10 keV, 10-20 keV, 20-30 keV, 30-56 keV )

6. Introduction: Object SPectral EXecutive (OSPEX)  Object Spectral Executive (OSPEX) software package written by R. Schwartz in 1995 inside SolarSoft.  SolarSoft is the complete package of the routines written in Interactive data language (IDL) and made available for the data analysis of different space and ground based missions viz. SOXS, RHESSI, SOHO, GOES.  The flare plasma parameters viz. temperature, emission measure, power-law index are estimated with the help of forward fitting the combination of thermal and non- thermal functions provided in OSPEX (Jain et al., 2008).  These parameters enable us to model the flare plasma condition during solar flare energy release.

7. Data Analysis in OSPEX  OSPEX run with IDL version 5.6 or later with Solarsoft SSW contains modules which can run at IDL command line or from GUI or combination of the both.  In OSPEX, the user reads and displays the input data, selects and subtracts background, selects time intervals of interest to study the flare, selects a combination of photon flux model components to describe the data, and fits those components to the spectrum in each time interval selected.  During the fitting process, the response matrix is used to convert the photon model to the model counts to compare with the input count data.  The resulting time-ordered fit parameters are stored and can be displayed and analyzed with OSPEX.  The entire OSPEX session can be saved in the form of a script and the fit results stored in the form of a FITS file.

8. Algorithms SOXS Data Conversion from Binary to ASCII format:  SOXS data packet is stored using structure in IDL which can be referenced directly anywhere in program. SOXS double bytes data stored MSB  LSB, while it reads as FIX function, convert into 16 bit integer in reverse order by adding 65536 (2 16 -1) to LSB. Single byte data stored as 8 bits integer.  Converted counts and spectral data for both Si and CZT detectors, Process Identification(PID) values which contains house keeping parameters to keep track on health of payload and Ground Receiving Time(GRT) in sec. for each record using above techniques. Detector Response:  Response is computed from the exposed geometric area through the collimator circle, the absorption from Beryllium (Be), Aluminium (Al), and Kapton and then the prob of single pe detection in Si.  Effective Area as a function of energy(keV) is calculated as Where µ ′ is the Attenuation Coefficient and t is the thickness of the filter (cm).

9. Count and Photon Spectra Conversion: Algorithms The efficiency factors (or conversion factors) is used to convert counts to photons depends on both the response matrix and a model. Efficiency factor = Count Spectrum / Photon Spectrum Photons to counts = Response matrix * photon spectrum Where response Matrix is calculated as follows:  Si Detector Response Matrix(DRM) is obtained by using default Efficiency and Effective Area as a function of Energy(keV) & Edges files and Full Width Half maximum (FWHM) 0.7 keV values.  It uses area of aperture as 0.091 cm^2. Energy calibration is fit and uses efficiency and Effective Area and smoothed to energy edge midpoints.  It uses photon spectrum (photons/cm^2/sec) as input and returns Si DRM as 256X256 array(cnts/cm^2/s/keV).  CZT DRM is obtained by using default values FWHM 2.0 keV, number of channel 238, gain 0.218750 keV per channel and Area 0.18 cm^2. It returns CZT DRM as 238X238 array from 4-56 keV for photon spectrum (i.e. Integrated over photon energy bins) in units of cnts/cm^2/s/keV.

10.  Analyzing flare is to compare the model photon flux with the observed photon flux and flare parameters corresponding to the closest model spectra is assigned to that observation.  The fit models provide parameters e. g. the temperature, the emission measure and the area of interaction used in the fitting process. Actual values of the flare model, called fit parameters, depends on the closeness of the fit and the fit model chosen. Each fit model has a varying amount of parameters, that may give different information about the flare.  For estimating plasma parameters related to Flare, OSPEX contains various Fit model functions,  Single power law function with epivot control allows users to set epivot (keV) and gives power law index.  Broken power law returns Break Energy (keV) and power law index for below and above break.  Exponential function gives Pseudo temperature.  Multi thermal function gives power law index for calculating differential emission measure at T=2 keV, 10^49 cm^(-3) keV(-1). It also returns minimum and maximum plasma temperature (keV). CHIANTI Version 6.0 enabled us to extract line information included in the observed spectrum for Fe and Fe/Ni line characteristic. Algorithms: Model Functions

11. References: 1. Rajmal Jain, Hemant Dave, A. B. Shah, N. M. Vadher, Vishal M. Shah, G. P. Ubale, K. S. B. Manian, Chirag M. Solanki, K. J. Shah, Sumit Kumar and 4 coauthors, Solar Phys., 227,89 (2005) 2. Rajmal Jain, Malini Aggarwal and Raghunandan Sharma, Journal of Astrophysics and Astronomy, 29, 125 (2008)