Preflare Heating and Mass Motion in a Solar Flare Associated with Hot Plasma Ejection: 1993 November 11 C9.7 Flare

Abstract

X-ray plasma ejection associated with an impulsive flare was observed near to the solar limb on 1993 November 11 with the Yohkoh soft X-ray telescope. We examined the physical condition as well as the morphological evolution of the ejecta and flare. The results are the following: (1) The shape of the ejecta was a loop before the start of ejection. (2) The ejected loop appeared after its footpoint brightened, and started to slowly rise long before the impulsive phase (at ∼ 10 km s⁻¹, the preflare slow rise), but was suddenly accelerated to ∼ 130 km s⁻¹ just before or at about the onset of the impulsive phase (the main rise). (3) The ejected material was already heated to ∼ 11.3 ± 4 MK before the main rise. (4) The electron density of the ejecta (∼ 4.5 × 10⁹−1.4 × 10¹⁰ cm⁻³) was larger than the typical density of the active-region corona. The mass of the ejecta was ∼ 10¹⁴ g. These results suggest chromospheric evaporation due to preflare heating. It is suggested that magnetic reconnection may already be occurring in the preflare phase, leading to heating of the ejected material (possibly plasmoids) and causing chromospheric evaporation. The reconnection rate (or the speed of the inflow into the neutral point) is also estimated for the preflare, the impulsive, and the gradual phases.