Energy-Dependent Timing of Thermal Emission in Solar Flares
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 (ne) varies in the range of ne=(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.
- Publication:
-
Solar Physics
- Pub Date:
- May 2011
- DOI:
- 10.1007/s11207-011-9754-1
- arXiv:
- arXiv:1103.5546
- Bibcode:
- 2011SoPh..270..137J
- Keywords:
-
- Conduction cooling;
- Solar flares: multi-thermal;
- nonthermal;
- Astrophysics - Solar and Stellar Astrophysics
- E-Print:
- Solar Physics, in press