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
presentation
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