Abstract
Some X-class flares (hot thermal flares, HTF) observed with the Hinotori satellite show unique behavior: slow time variability, a compact hard X-ray source containing dense (n > 1011 cm−3) and hot (T > 3 × 107 K) plasma, and unusually weak microwave emission in spite of the intense magnetic field (B > 330 G) required theoretically to sustain the hot plasma. These observations show that HTF's have essentially thermal characteristics throughout the flare evolution, while in impulsive flares, there is a transition in the energy release mode from particle acceleration (impulsive phase) to plasma heating (gradual phase). This behavior can be explained in a unified manner by employing parallel DC electric field acting over large distances.
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Tsuneta, S. Impulsive and hot thermal solar flares. Sol Phys 113, 35–48 (1987). https://doi.org/10.1007/BF00147680
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DOI: https://doi.org/10.1007/BF00147680