5. Dynamics of the Energy Spectrum of the Hard X-Ray Emission of a
Solar Flare With the Second Time Resolution
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Figure 5
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[39] Figure 5 shows in the
logarithmic-scale spectra of the flare on 29 October 2002 measured
with the 1-s interval and averaged over 10 s (thick line). This
flare draws attention by its spectrum of hard X-ray emission. At
the growth (Figure 5a) and maximum (Figure 5b) phases, a spectrum
is formed having a complicated form. The spectrum may be
conventionally split into components with the point of inflection
at
45 keV. Part of the spectrum in the region of small energies
up to the inflection point probably is a thermal emission of the
hot plasma, whereas in the high-energy region (above this point)
is explained by the bremsstrahlung of fast electrons. Such form of
the spectrum is conserved also at the flare decay (Figure 5c).
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Figure 6
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[40] The fact that the spectrum becomes steeper with an energy increase
is another characteristic feature of this flare. One can explain
such behavior of the spectrum if the distribution function of
quick electrons generating bremsstrahlung X-ray emission may have
a cut off at some maximum velocity
V max
(for the given flare
V max corresponds to the energy of about 160 keV), which may be a result
of nonlinear interaction of these electrons with plasma waves
[Kudryavtsev and Charikov, 1999;
Kudryavtsev et al., 2002;
Levitinsky and Shashurin, 1967]. The continuation of electron
acceleration at the stage of emission decay is the next
interesting feature of this flare. Figure 6 shows the averaged
over the 10-s interval spectra at the growth, maximum, and decay
phases. One can see from Figure 6 that in the beginning of the
decay phase the intensity of the emission with the energy above
100 keV exceeds the intensity in the maximum, this fact
manifesting appearance of higher-energy electrons.
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