[论文解读] Fine structure and long duration of a flare coronal X-ray source with RHESSI and SDO/AIA data

S. Kołomański, Tomasz Mrozek+1 more|arXiv (Cornell University)|Jan 31, 2017

Solar and Space Plasma Dynamics被引用 3

一句话总结

本研究利用RHESSI硬X射线与SDO/AIA EUV的同步观测，调查了SOL2011-10-22耀斑中日冕X射线源（CXS）的精细结构及其长期持续性。尽管成像分辨率较高，CXS中未检测到任何小尺度结构，表明其为平滑且无结构的，而其长达5小时的持续时间可能由持续的磁重连作用维持，这一点由同期的拱弧上方下冲流（SADs）和10–15 MK范围内的持续热辐射所支持。

ABSTRACT

Coronal X-ray sources (CXSs) are phenomenon very often occurring in solar flares regardless of a flare size, duration or power. The nature of the sources was difficult to uncover for many years. It seems that at last, combining data from RHESSI and SDO/AIA, there is a unprecedented possibility to 'look inside' CXSs and to answer the questions about their formation, evolution and structure. We present a study of a CXS of the SOL2011-10-22T11:10 long-duration flare observed simultaneously with RHESSI and SDO/AIA. We focus our attention on the following questions: What was responsible for the CXS presence and long duration? Was there any fine structure in the CXS? Available data enables us to study a relation between the CXS and structures observed in EUV during the decay phase of the flare. X-ray emission recorded by RHESSI during the decay phase of the flare came from about 10 MK hot CXS. The source was observable for 5 hours. This long presence of the source could be supported by magnetic reconnection ongoing during the decay phase. Supra-arcade downflows, which are considered to be a manifestation of magnetic reconnection, were observed at the same time as the CXS. The source was co-spatial with the part of the hot supra-arcade region that had the highest emission measure and simultaneously the temperature within the range of RHESSI thermal-response. However, while the supra-arcade region was a dynamic region consisting of small-scale structures, the CXS seemed to be smooth, structureless. We run simulations using real and synthetic RHESSI data, but we did not find any strong evidence that the CXS had any small-scale structure.

研究动机与目标

• 调查耀斑中日冕X射线源（CXS）的精细结构及其长期持续性。
• 利用高分辨率X射线与EUV数据，确定CXS是否表现出小尺度结构。
• 评估磁重连在长时间维持CXS中的作用。
• 评估是否需要能量与质量约束机制来解释CXS的长期存在。
• 通过对比观测到的X射线与EUV结构，检验CXS由未分辨的高温环构成的假设。

提出的方法

• 对RHESSI硬X射线成像与光谱数据及SDO/AIA EUV观测进行同步分析，以关联X射线与EUV结构。
• 利用RHESSI数据重建X射线图像并执行成像光谱分析，重点研究10–15 MK范围内的热发射。
• 应用Palermo-Harvard（PH）一维流体动力学模型，模拟在真实加热条件下且无质量/能量流出限制下回缩环（RLs）的冷却过程。
• 对半长L = 9×10⁹ cm的耀斑环进行建模，加热至10–15 MK，密度为4–9×10⁹ cm⁻³，随后在突然停止加热后模拟其冷却过程。
• 将模拟的冷却时间与观测到的CXS持续时间（5小时）进行比较，以评估约束机制的作用。
• 利用合成RHESSI数据和真实数据模拟，测试在CXS中检测小尺度结构的可能性。

实验结果

研究问题

• RQ1 在SOL2011-10-22耀斑中观测到的日冕X射线源（CXS）在亚角秒分辨率下是否表现出精细结构？
• RQ2 考虑到预期的热冷却 timescales，是什么物理机制使CXS持续超过5小时？
• RQ3 CXS与拱弧上方下冲流（SADs）在空间和时间上是否存在相关性，表明磁重连仍在持续？
• RQ4 CXS的观测X射线辐射是否可由未分辨的高温环解释，还是该源确实无结构？
• RQ5 RHESSI数据中未检测到明显的小尺度结构，是否意味着CXS是平滑的，还是受仪器分辨率限制？

主要发现

• 日冕X射线源（CXS）持续了5小时，其X射线辐射来自温度约为10 MK的等离子体，与热发射一致。
• CXS与拱弧区域最热、最致密的部分在空间上共轭，根据发射量和温度测量结果，且与RHESSI热响应函数对齐。
• 尽管AIA和RHESSI数据分辨率较高，CXS中仍未检测到任何小尺度结构，表明其在仪器分辨率下呈现平滑且无结构的特征。
• 利用真实与合成RHESSI数据的模拟未发现小尺度结构的有力证据，表明若存在此类特征，其尺度可能低于探测阈值。
• 对回缩环（RLs）的流体动力学建模显示，冷却时间为3500–5500秒（≈58–92分钟），与观测持续时间相符，且无需显著的能量或质量约束即可维持该源。
• 在衰减阶段观测到的拱弧上方下冲流（SADs）支持磁重连仍在持续，这可能是维持CXS能量输入的关键机制。