Energy-Dependent Timing of Thermal Emission in Solar Flares |
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Authors: | Rajmal Jain Arun Kumar Awasthi Arvind Singh Rajpurohit Markus J. Aschwanden |
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Affiliation: | (1) Astronomy and Astrophysics Group, Dept. of Physics and Astronomy, University of Glasgow, Glasgow, G12 8QQ, U.K.;(2) Solar & Astrophysics Laboratory, Dept. L9-41, Lockheed Martin Advanced Technology Center, Bldg.252, 3251 Hanover St., Palo Alto, CA, 94304, U.S.A. |
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Abstract: | We report solar flare plasma to be multi-thermal in nature based on the theoretical model and study of the energy-dependent timing of thermal emission in ten M-class flares. We employ high-resolution X-ray spectra observed by the Si detector of the “Solar X-ray Spectrometer” (SOXS). The SOXS onboard the Indian GSAT-2 spacecraft was launched by the GSLV-D2 rocket on 8 May 2003. Firstly we model the spectral evolution of the X-ray line and continuum emission flux F(ε) from the flare by integrating a series of isothermal plasma flux. We find that the multi-temperature integrated flux F(ε) is a power-law function of ε with a spectral index (γ)≈−4.65. Next, based on spectral-temporal evolution of the flares we find that the emission in the energy range E=4 – 15 keV is dominated by temperatures of T=12 – 50 MK, while the multi-thermal power-law DEM index (δ) varies in the range of −4.4 and −5.7. The temporal evolution of the X-ray flux F(ε,t) assuming a multi-temperature plasma governed by thermal conduction cooling reveals that the temperature-dependent cooling time varies between 296 and 4640 s and the electron density (n e) varies in the range of n e=(1.77 – 29.3)×1010 cm−3. Employing temporal evolution technique in the current study as an alternative method for separating thermal from nonthermal components in the energy spectra, we measure the break-energy point, ranging between 14 and 21±1.0 keV. |
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