Quantitative analysis of nonthermal electrons in impulsive hard X-ray flares

T. Minoshima and T. Yokoyama

We present a quantitative study of nonthermal electrons in solar hard X-ray flares. In this study, the lower energy cutoff (Ec) in the spectrum of nonthermal electrons is a key variable. Instead of adopting the usual assumption of Ec to be a fixed value (20 keV or 30 keV), we derive the lower energy cutoff by assuming that the total energy of nonthermal electrons released during the impulsive phase equals the increase in the thermal energy of the soft X-ray emitting flare plasma during the impulsive phase. We successfully estimate several physical variables of nonthermal electrons in the impulsive phase of the flares. What we find in this analysis are as follows: (1) The values of the derived Ec are ranging in 20 - 45 keV. (2) There is a positive correlation between the nonthermal electron rate in the impulsive phase and the number density of the soft X-ray emitting flare plasma in the pre-impulsive phase. (3) There is a positive correlation between the derived lower energy cutoff and hard X-ray sources separation distance. We discuss electron acceleration in solar flares based on these results.

Correspondence

Takashi Minoshima (takashim@eps.s.u-tokyo.ac.jp), University of Tokyo

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