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arXiv · 1801.06755

Observations of Electron-driven Evaporation during a Flare Precursor

Dong Li·Ying Li·Wei Su·Yu Huang·Zongjun Ning
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Abstract

We investigate the relationship between the blue shifts of a hot emission line and the nonthermal emissions in microwave and hard X-ray (HXR) wavelengths during the precursor of a solar flare on 2014 October 27. The flare precursor is identified as a small but well-developed peak in soft X-ray and extreme-ultraviolet passbands before the GOES flare onset, which is accompanied by a pronounced burst in microwave 17 & 34 GHz and HXR 25-50 keV. The slit of Interface Region Imaging Spectrograph (IRIS) stays at one ribbon-like transient during the flare precursor, where shows visible nonthermal emissions in NoRH and RHESSI images. The IRIS spectroscopic observations show that the hot line of Fe XXI 1354.09 A (logT ~ 7.05) displays blue shifts, while the cool line of Si IV 1402.77 A (logT ~ 4.8) exhibits red shifts. The blue shifts and red shifts are well correlated to each other, indicative of an explosive chromospheric evaporation during the flare precursor particularly combining with a high nonthermal energy flux and a short characteristic timescale. In addition, the blue shifts of Fe XXI 1354.09 A are well correlated with the microwave and HXR emissions, implying that the explosive chromospheric evaporation during the flare precursor is driven by nonthermal electrons.

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Dong Li, Ying Li, Wei Su, Yu Huang, Zongjun Ning. 2018-01-21. Observations of Electron-driven Evaporation during a Flare Precursor. https://doi.org/10.3847/1538-4357/aaa9c0

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