Study of Particle Acceleration and Magnetic Field Structure in Solar Flares

利用Yohkoh卫星上的硬X射线望远镜（HXT）研究了太阳耀斑硬X射线足点源的时间演化，研究了与耀斑和粒子加速过程有关的磁场结构。在观测到的耀斑中，2000年7月14日开始的一次大耀斑提供了一个非常详细地研究硬X射线足点源的独特机会。对这个耀斑的分析揭示了一个惊人的结果，即非热（30 keV以上）足点源显示出一对细长的带状物，这使人想起了H-α观测中所谓的“双带结构”。这表明，磁拱廊结构，而不是一个单一的环，应该参与太阳耀斑能量释放。对足点源的详细分析表明，磁剪切随着耀斑的发展而减小，并且源趋向于显示出朝向外缘的较硬的谱。这些观测结果有望为研究耀斑粒子加速机制提供重要线索。除了硬X射线足点源的分析，理论研究，刺激的分析，一直在进行中，试图了解太阳耀斑能量释放的三维磁场重联的框架。

By studying temporal evolution of solar flare hard X-ray footpoint sources with the Hard X-ray Telescope (HXT) aboard Yohkoh satellite, we have investigated magnetic field structure associated with flares and particle acceleration process(es). Amongst flares observed, a large flare which commenced on 14 July, 2000 has provided a unique opportunity to study hard X-ray footpoint sources in great detail. Analysis of this flare revealed a striking result that non-thermal (above 30 keV) footpoint sources show a pair of thin elongated ribbons which reminds one the so-called "two-ribbon structure" in H-alpha observations. This suggests that magnetic arcade structure, not just a single loop, should take part in solar flare energy release. Detailed analysis on the footpoint sources has indicated that magnetic shear decreases as the flare progresses, and that the sources tend to show harder spectra towards outer edges. These observational findings are expected to provide important clues for investigating particle acceleration mechanisms in flares. In addition to analyses of hard X-ray footpoint sources, theoretical studies, stimulated with the analyses, have been in progress with an attempt to understand solar flare energy release in the framework of 3-dimensional magnetic reconnection.