Solar x-ray spectrometer (SOXS) mission – Low energy payload – First results

Abstract

We present the first results from the ‘Low Energy Detector’ pay-load of ‘Solar X-ray Spectrometer (SOXS)’ mission, which was launched onboard GSAT-2 Indian spacecraft on 08 May 2003 by GSLV-D2 rocket to study the solar flares. The SOXS Low Energy Detector (SLD) payload was designed, developed and fabricated by Physical Research Laboratory (PRL) in collaboration with Space Application Centre (SAC), Ahmedabad and ISRO Satellite Centre (ISAC), Bangalore of the Indian Space Research Organization (ISRO). The SLD payload employs the state-of-the-art solid state detectors viz., Si PIN and Cadmium-Zinc-Telluride (CZT) devices that operate at near room temperature (-20°C). The dynamic energy range of Si PIN and CZT detectors are 4–25 keV and 4–56 keV respectively. The Si PIN provides sub-keV energy resolution while CZT reveals ∼1.7keV energy resolution throughout the dynamic range. The high sensitivity and sub-keV energy resolution of Si PIN detector allows the measuring of the intensity, peak energy and equivalent width of the Fe-line complex at approximately 6.7 keV as a function of time in all 8 M-class flares studied in this investigation. The peak energy (E p) of Fe-line feature varies between 6.4 and 6.8 keV with increase in temperature from 9 to 34 MK. We found that the equivalent width (ω) of Fe-line feature increases exponentially with temperature up to 20 MK but later it increases very slowly up to 28 MK and then it remains uniform around 1.55 keV up to 34 MK. We compare our measurements ofw with calculations made earlier by various investigators and propose that these measurements may improve theoretical models. We interpret the variation of both Epand ω with temperature as the changes in the ionization and recombination conditions in the plasma during the flare interval and as a consequence the contribution from different ionic emission lines also varies.