Electron Distribution and Energy Release in Magnetic Reconnection Outflow Regions during the Pre-impulsive Phase of a Solar Flare
Electron Distribution and Energy Release in Magnetic Reconnection Outflow Regions during the Pre-impulsive Phase of a Solar Flare
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DOI：
10.3847/1538-4357/ab01c9
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发表时间：
2019-01
期刊：
影响因子：
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通讯作者：
M. Battaglia;E. P. Kontar;G. Motorina
中科院分区：
文献类型：
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作者：
M. Battaglia;E. P. Kontar;G. Motorina
我们提出了在太阳耀斑前脉冲阶段的磁重联外流中的电子轰击观测SOL 2012 -07- 19 T05：58。在大约20分钟的时间间隔内，从脉冲阶段开始前40分钟开始，在日冕中观察到两个X射线源，一个在假定的重联区域上方，一个在下方。对于这两个源，作为时间的函数的平均电子分布函数被确定在从0.1千电子伏到几十千电子伏的能量范围内，为第一次。这是通过X射线和极紫外（EUV）数据的同时前向拟合来完成的。使用RHESSI的成像光谱提供了有关这些源中电子分布的高能尾部的信息，而来自SDO/大气成像装置的EUV图像用于限制低比电子能量。在磁场重联流出中测得的电子分布谱与κ = 3.5-5.5的随时间演化的κ分布一致。光谱演变表明，电子被加速到逐步更高的能量在源以上的重联区域，而在下面的源，光谱形状不改变，但观察到的排放措施的整体增加，这表明密度增加由于蒸发。能量从源极区传输出去的主要机制是传导和自由流动的电子。后者占主导地位的一个以上的数量级，是典型的非热能量在硬X射线峰的太阳耀斑，这表明有效的加速，即使在这个早期阶段的事件。
We present observations of electron energization in magnetic reconnection outflows during the pre-impulsive phase of solar flare SOL2012-07-19T05:58. During a time-interval of about 20 minutes, starting 40 minutes before the onset of the impulsive phase, two X-ray sources were observed in the corona, one above the presumed reconnection region and one below. For both of these sources, the mean electron distribution function as a function of time is determined over an energy range from 0.1 keV up to several tens of keV, for the first time. This is done by simultaneous forward fitting of X-ray and extreme ultraviolet (EUV) data. Imaging spectroscopy with RHESSI provides information on the high-energy tail of the electron distribution in these sources while EUV images from SDO/Atmospheric Imaging Assembly are used to constrain the low specific electron energies. The measured electron distribution spectrum in the magnetic reconnection outflows is consistent with a time-evolving kappa-distribution with κ = 3.5–5.5. The spectral evolution suggests that electrons are accelerated to progressively higher energies in the source above the reconnection region, while in the source below, the spectral shape does not change but an overall increase of the emission measure is observed, suggesting density increase due to evaporation. The main mechanisms by which energy is transported away from the source regions are conduction and free-streaming electrons. The latter dominates by more than one order of magnitude and is comparable to typical nonthermal energies during the hard X-ray peak of solar flares, suggesting efficient acceleration even during this early phase of the event.