YOHKOH残留物：硬X射线中部分遮蔽的耀斑
YOHKOH remnants: partially occulted flares in hard X-rays
摘要：
耀斑被太阳边缘部分掩盖，是我们对硬X射线环顶源的最好的知识库。最近，RHESSI观测到的部分遮蔽耀斑的调查已经发表（Krucker & Lin 2008）。YOHKOH庞大的数据库仍有待开展此类活动。这项工作就是试图填补这一空白。在YOHKOH硬X射线望远镜耀斑目录中的1286个耀斑中，我们确定了98个发生在太阳边缘之后的事件。我们研究了它们的硬X射线光谱和空间结构。我们发现，在大多数情况下，部分掩星耀斑的硬X射线谱由两个分量组成，非热和热，这是共空间的。部分掩星耀斑的光子能谱比非掩星耀斑的能谱系统地陡。这样的差异，我们解释作为一个结果，本质上不同的条件统治的日冕部分的耀斑，在比较的足迹，通常占主导地位的硬X射线发射的磁盘耀斑。造成这种差异的原因至少有两个：（1）热等离子体发射对硬X射线的污染较强，（2）非热电子辐射能量的机制不同。薄靶机制负责环顶源的硬X射线发射和厚靶机制负责足点源的发射的示意图，可以通过一些日冕厚靶源的存在来修改。其中至少有一部分表明是磁性陷阱。研究的耀斑对日冕的全球磁结构没有响应。对于它们的特征，决定性的是它们形成时的局部磁结构。
英文摘要：
Flares being partially occulted by the solar limb, are the best reservoir of our knowledge about hard X-ray loop-top sources. Recently, the survey of partially occulted flares observed by the RHESSI has been published (Krucker & Lin 2008). The extensive YOHKOH database still awaits such activities. This work is an attempt to fill this gap. Among from 1286 flares in the YOHKOH Hard X-ray Telescope Flare Catalogue, for which the hard X-ray images had been enclosed, we identified 98 events that occurred behind the solar limb. We investigated their hard X-ray spectra and spatial structure. We found that in most cases the hard X-ray spectrum of partially occulted flares consists of two components, non-thermal and thermal, which are co-spatial. The photon energy spectra of the partially occulted flares are systematically steeper than spectra of the non-occulted flares. Such a difference we explain as a consequence of intrinsically dissimilar conditions ruling in coronal parts of flares, in comparison with the footpoints which usually dominate the hard X-ray emission of disk flares. At least two reasons of the difference should be taken into consideration: (1) stronger contamination of hard X-rays with emission of thermal plasma, (2) different mechanism in which non-thermal electrons radiate their energy. A schematic picture, in which thin-target mechanism is responsible for hard X-ray emission of loop-top sources and thick-target mechanism -- for emission of footpoint sources, can be modified by the presence of some coronal thick-target sources. At least a part of them suggests a magnetic trapping. Investigated flares do not respond the global magnetic configuration of the solar corona. For their characteristics conclusive is rather the local magnetic configuration in which they were developed.
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