Impact of X-Ray Observations from the Hinotori Satellite on Solar Flare Research

Abstract

Abstract The X-ray observations of solar flares from the Hinotori satellite are extensively discussed. Complex flare variety in the X-ray time profile, spectrum, and morphology is elucidated by considering three flare types (A, B, and C) and also five emission components. Various X-ray morphology and evolutionary characteristics are discussed in comparison with optical data. The type B (impulsive) flare is suggested to occur in complexly sheared low-lying fields after their separation from the erupted filament, followed by progressive energy releases at higher loop arcades in the gradual phase. The type C (gradual-hard) flare shows long-enduring energy releases at high loops with weak shear. Spectral hardening is shown to proceed with systematic shifts of the hard X-ray source to higher altitudes. The soft X-ray diagnostics of the hot flare plasmas are extensively discussed covering flare temperature diagnosis by Fe xxvi, Fe xxv, and continuum spectra, early development and the relation of nonthermal line broadening and blueshift, Ka diagnosis, and line polarization. The hot thermal source (Te3 × 107 K) emitting Fe xxvi and hard X-rays (<40 keV) is identified with the loops of high density and high field strength, originally confined at one leg of the erupted prominence, and shows sequential formation at higher altitudes. Suppression of acceleration in type A flares is suggested. A hybrid origin of the hot plasmas is implied from evidence for both evaporative supply and coronal in-situ heating. A large coronal energy deposit due to in-situ heating and dissipation of lowenergy electrons is argued to support the conduction-driven evaporation. Observed flare variety is suggested to result from the diversity of intrinsic magnetic shear and ambient density in different magnetic-tube configurations that originate in the convection zone. A magnetic morphology of flares is suggested together with a general flare scenario.