Mutual Dependence of Physical Variables in Hard X-ray Flares Observed with Yohkoh

1. Mutual Dependence of Physical Variables in Hard X-ray Flares Observed with Yohkoh T. Minoshima, T. Yokoyama (Univ. of Tokyo) Nobeyama symposium 2004 @ Kiyosato

2. Introduction Electron lower energy cutoff(Ec) • To estimate physical variables of non-thermal component, the determination of the lower energy cutoff is important. • It determines the total number and energy of non-thermal electrons. • It may be related to the acceleration mechanism. • However, it is not easy to obtain it directly from the observed HXR spectrum. We try to deduce it indirectly with some assumptions.

3. Energy integration The thick -target model Electrons energy spectrum HXR dEnonthe/dt Analysis method • LHS is obtained as a function of Ec which is assumed to be time-independent. • DEthe is estimated from soft X-ray observational data. • a is assumed to be unity. Ec is deduced.

4. Analysis samples

5. Thermal energy [erg] (linear scale) HXT [M2:CTS/SEC/SC] (linear scale) 150 2×1031 ←T90 line SXT satu. 100 Pre- impulsive 1031 50 0 0 UT Example2001/04/12 X2.0 • HXR ⇒ Enonthe • Comparing Enonthe with DEthe ⇒ optimal Ec • Estimate non-thermal variables

6. Analysis results(HXR peak count rate vs Lower energy cutoff) 50 40 Relatively high The color of symbols : classification of Ec Ec 30 20 Relatively low 10 0 4000 6000 2000 HXT [M2:CTS/SEC/SC]

7. 6 5 4 Break down g(M2/M1) 3 Break up 2 1 1 2 3 4 5 6 g(M1/L) HXR spectral analysis in the initial phase(when the derived Ec is relatively high) log I Bare non-thermal (Double power-law fitting) Time：red→black

8. Dependence of non-thermal electrons production rate dN/dt [sec-1] 1037 1036 1035 109 1010 1011 npre [cm-3]

9. Summary We analyze 7 HXR flares to examine mutual dependence of physical variables with some assumptions (see §2). The results are as follows: 1. The derived lower energy cutoff in the spectrum of non-thermal electrons is ranging in 20-40 keV. 2. When the derived lower energy cutoff in the spectrum of non-thermal electrons is relatively high (>30 keV), the observed HXR spectrum shows the broken-down form at 25-28 keV in the initial phase. This relationship is not inconsistent with calculation results (Gan et al. 2001). 3. When the derived lower energy cutoff in the spectrum of non-thermal electrons is relatively low (<30 keV), on the other hand, the observed HXR spectrum indicates the existence of super-hot thermal plasma in the initial phase. 4. Positive correlation between the derived non-thermal electrons production rate and the derived thermal plasma density in the pre-impulsive phase is found.