arXiv 2007.104432020-07-23astro-ph.SR

长时间太阳耀斑脉冲后阶段期间的磁重联：作为微波和X射线爆发原因的双向流出

Magnetic Reconnection During the Post-Impulsive Phase of a Long-Duration Solar Flare: Bi-Directional Outflows as a Cause of Microwave and X-ray Bursts

Sijie Yu, Bin Chen, Katharine K. Reeves, Dale E. Gary, Sophie Musset, Gregory D. Fleishman, Gelu M. Nita, Lindsay Glesener

备注：: 19 pages, 11 figures, accepted for publication in ApJ
DOI：: 10.3847/1538-4357/aba8a6

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摘要：

磁重联在为太阳耀斑提供动力、高能粒子的产生和等离子体加热方面起着至关重要的作用。然而，磁重联发生在哪里，释放的磁能如何和在哪里被传输，以及它如何被转换为其他形式仍然不清楚。在这里，我们报告了在2017年9月10日X8.2太阳耀斑的脉冲后逐渐阶段期间，在极紫外线发射和散射白光中观察到的大规模等离子体片内反复出现的双向等离子体流出。每一个双向流出起源于等离子体片从一个离散的网站，确定为一个磁重联网站。这些重联点位于耀斑拱廊顶部上方非常低的高度（$< 180$ Mm，或0.26 $R_{\odot}$），距离仅为等离子体片总长度的$<3\%$，延伸到至少10 $R_{\odot}$。每次到达环顶区的向阳外流似乎与环顶区的一个以热源（10-20 MK）为主的脉冲微波和X射线爆发相一致，紧接着是位于环管区的一个非热微波爆发。我们提出重联流出将局部磁重联点释放的磁能以动能通量和/或电磁坡印亭通量的形式向外传输。指向太阳的能量通量在耀斑后的拱廊中引起粒子加速和等离子体加热，被观测为热的和非热的耀斑发射。

英文摘要：

Magnetic reconnection plays a crucial role in powering solar flares, production of energetic particles, and plasma heating. However, where the magnetic reconnections occur, how and where the released magnetic energy is transported, and how it is converted to other forms remain unclear. Here we report recurring bi-directional plasma outflows located within a large-scale plasma sheet observed in extreme ultraviolet emission and scattered white light during the post-impulsive gradual phase of the X8.2 solar flare on 2017 September 10. Each of the bi-directional outflows originates in the plasma sheet from a discrete site, identified as a magnetic reconnection site. These reconnection sites reside at very low altitudes ($< 180$ Mm, or 0.26 $R_{\odot}$) above the top of the flare arcade, a distance only $<3\%$ of the total length of a plasma sheet that extends to at least 10 $R_{\odot}$. Each arrival of sunward outflows at the looptop region appears to coincide with an impulsive microwave and X-ray burst dominated by a hot source (10-20 MK) at the looptop, which is immediately followed by a nonthermal microwave burst located in the loopleg region. We propose that the reconnection outflows transport the magnetic energy released at localized magnetic reconnection sites outward in the form of kinetic energy flux and/or electromagnetic Poynting flux. The sunward-directed energy flux induces particle acceleration and plasma heating in the post-flare arcades, observed as the hot and nonthermal flare emissions.

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