K. J. Shah

 Physical Research Laboratory

(Unit of Dept. of Space, Govt. of India)Navrangpura, Ahmedabad – 380 009

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)

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)

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 1F Phase 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

Byte Detail For Various Phases

Search / Quiet Phase:

8 Bytes Header 638 Bytes Spectral Data 54 Bytes Temporal Data

8 Bytes Header 638 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 BytesSi – 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 )

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.

Data Analysis in OSPEXOSPEX 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.

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 (216-1) 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).

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.

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

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)