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arXiv 1102.3664astro-ph.SRastro-ph.HEphysics.plasm-phphysics.space-ph
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太阳耀斑环中高能电子的加速、磁涨落和跨场输运

Acceleration, magnetic fluctuations and cross-field transport of energetic electrons in a solar flare loop

E. P. Kontar, I. G. Hannah, N. H. Bian

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6 pages, 4 figures, submitted to ApJL
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摘要：

等离子体湍流被认为与太阳耀斑中涉及的各种物理过程有关，包括磁重联、粒子加速和输运。利用Ramaty高能太阳光谱成像仪（{ \it RHESSI}）的观测和X射线可见度分析，我们确定了一次耀斑（GOES M3.7级，2002年4月14日23 $:$ 55 UT）的高能电子的空间和光谱分布，这一耀斑以前被认为与重联情景相一致。结果表明，由于环中存在高密度等离子体，电子必须绕长$\sim 2\times 10^9$ cm、宽$\sim 7\times 10^8$ cm的环顶点连续加速。几十keV的电子的能量依赖的运输被观察到发生沿和跨引导磁场的环路。我们表明，交叉场运输是一致的磁湍流的存在下，在循环中，电子被加速，并估计的大小的场线扩散系数的耀斑的不同阶段。在给定的磁场关联长度下，计算了磁涨落的能量密度，它大于非热电子的能量密度。当最大数量的电子被加速时，磁波动的水平达到峰值，并且在衰变阶段低于可检测性或不存在。这些硬X射线观测提供了第一个观测证据，证明磁湍流控制着致密耀斑环中高能电子的演化，并暗示了它们的湍流加速。

英文摘要：

Plasma turbulence is thought to be associated with various physical processes involved in solar flares, including magnetic reconnection, particle acceleration and transport. Using Ramaty High Energy Solar Spectroscopic Imager ({\it RHESSI}) observations and the X-ray visibility analysis, we determine the spatial and spectral distributions of energetic electrons for a flare (GOES M3.7 class, April 14, 2002 23$:$55 UT), which was previously found to be consistent with a reconnection scenario. It is demonstrated that because of the high density plasma in the loop, electrons have to be continuously accelerated about the loop apex of length $\sim 2\times 10^9$cm and width $\sim 7\times 10^8$cm. Energy dependent transport of tens of keV electrons is observed to occur both along and across the guiding magnetic field of the loop. We show that the cross-field transport is consistent with the presence of magnetic turbulence in the loop, where electrons are accelerated, and estimate the magnitude of the field line diffusion coefficient for different phases of the flare. The energy density of magnetic fluctuations is calculated for given magnetic field correlation lengths and is larger than the energy density of the non-thermal electrons. The level of magnetic fluctuations peaks when the largest number of electrons is accelerated and is below detectability or absent at the decay phase. These hard X-ray observations provide the first observational evidence that magnetic turbulence governs the evolution of energetic electrons in a dense flaring loop and is suggestive of their turbulent acceleration.

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