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arXiv 1406.4233astro-ph.SR
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太阳风源区磁重联产生超晕电子的数值模拟

Numerical Simulation of Superhalo Electrons Generated by Magnetic Reconnection in the Solar Wind Source Region

L. -P. Yang, L. -H. Wang, J. -S. He, C. -Y. Tu, S. -H. Zhang, L. Zhang, X. -S. Feng

摘要:

超晕电子似乎是连续存在于行星际介质中,即使在非常安静的时间,与幂律谱能量高于$\sim$ 2千电子伏。在这里,我们数值研究超晕电子的产生磁重联在太阳风源区,使用MHD和测试粒子模拟单X线重联和多X线重联。我们发现,直流电场,产生的磁重联区,可以加速电子从T $\sim10^5$ K的初始热能高达数百keV。加速后,一部分加速的电子与由重联驱动的新生太阳风流一起沿着新打开的磁力线向上传播到行星际空间,而其余的则向下移动到低层大气中。类似于在1 AU处观察到的超晕电子,向上行进的加速电子的通量与能量的关系在$\sim$ 2 $-$ 100 keV处显示出幂律分布,$f(E) \sim E^{-δ}$,$δ$为$\sim$ 1.5 $-$ 2.4。对于单(多)X线重联,随着异常电阻率参数$α$(均匀电阻率$η$)的增加,谱变得更硬(更软)。这些模拟结果表明,在太阳风源区的加速可能有助于超晕电子。

英文摘要:

Superhalo electrons appear to be continuously present in the interplanetary medium, even at very quiet times, with a power-law spectrum at energies above $\sim$2 keV. Here we numerically investigate the generation of superhalo electrons by magnetic reconnection in the solar wind source region, using the MHD and test particle simulations for both single X-line reconnection and multiple X-line reconnection. We find that the direct current electric field, produced in the magnetic reconnection region, can accelerate electrons from an initial thermal energy of T $\sim10^5$ K up to hundreds of keV. After acceleration, some of the accelerated electrons, together with the nascent solar wind flow driven by the reconnection, propagate upwards along the newly-opened magnetic field lines into the interplanetary space, while the rest move downwards into the lower atmosphere. Similar to the observed superhalo electrons at 1 AU, the flux of the upward-traveling accelerated electrons versus energy displays a power-law distribution at $\sim$ 2 $-$ 100 keV, $f(E) \sim E^{-δ}$, with a $δ$ of $\sim$ 1.5 $-$ 2.4. For single (multiple) X-line reconnection, the spectrum becomes harder (softer) as the anomalous resistivity parameter $α$ (uniform resistivity $η$) increases. These modeling results suggest that the acceleration in the solar wind source region may contribute to superhalo electrons.

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