The existence of hot X-ray onsets in solar flares
The existence of hot X-ray onsets in solar flares
复制标题
太阳耀斑中存在热X射线爆发
DOI：
10.1051/0004-6361/202347706
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发表时间：
2023
影响因子：
6.5
通讯作者：
Battaglia A
中科院分区：
文献类型：
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作者：
Battaglia A
背景科学界都知道，太阳耀斑活动往往在主要的脉冲能量释放之前很久就开始了。我们的目标是研究太阳轨道器/STIX观测到的四个不同耀斑的最早阶段，并确定新加热的等离子体与耀斑结构和动力学的关系。方法分析从地球和太阳轨道器观测到的四个事件，以便将STIX观测与GOES/XRS和SDO/AIA的观测结果进行比较。利用STIX和GOES光谱分析研究了事件的早期阶段，以研究等离子体物理参数的演变，包括等温温度和发射测量。此外，为了确定加热等离子体的位置，STIX观测与AIA图像相结合。结果在脉冲阶段之前有明显发射的事件从一开始就显示出温度升高(>；10 MK)，这表明能量释放在STIX检测之前就开始了。虽然温度在初始阶段几乎没有变化，但排放测量增加了大约两个数量级，这意味着一系列更大的能量释放。STIx和Goes的光谱分析表明，该辐射具有多热性质，热成分超过10 MK。在这一阶段，替代加热机制可能更为重要，因为STIX观察到的非热辐射只是在较晚的时候才被检测到。STIX和AIA图像显示，耀斑早期存在更致密的热等离子体源，它们来自与耀斑后期观察到的标准环顶源不同的位置。然而，由于扩展的韧致辐射源比致密源更难探测到，在热启动时，环顶可能有额外的加热等离子体。结论这一分析证实了“热启动”的存在，STIX甚至比GOES更早地发现了热启动模式。这些升高的温度意味着，能量释放实际上在STIX检测到之前就已经开始了。因此，热起始点可能对太阳耀斑的启动、早期发展甚至预测具有重要意义。
ContextIt is well known among the scientific community that solar flare activity often begins well before the main impulsive energy release. However, a consistent explanation for this phenomenon has not yet been established.AimsOur aim is to investigate the earliest phase of four distinct flares observed by Solar Orbiter/STIX and determine the relationships of the newly heated plasma to flare structure and dynamics.MethodsThe analysis focuses on four events that were observed from both Earth and Solar Orbiter, which allows for a comparison of STIX observations with those of GOES/XRS and SDO/AIA. The early phases of the events were studied using STIX and GOES spectroscopic analysis to investigate the evolution of the physical parameters of the plasma, including the isothermal temperature and emission measure. Furthermore, to determine the location of the heated plasma, STIX observations were combined with AIA images.ResultsThe events with clear emission prior to the impulsive phase show elevated temperatures (> 10 MK) from the very beginning, which indicates that energy release started before any detection by STIX. Although the temperature shows little variation during the initial phase, the emission measure increases by about two orders of magnitude, implying a series of incrementally greater energy releases. The spectral analysis of STIX and GOES from the very first time bins suggests that the emission has a multi-thermal nature, with a hot component of more than 10 MK. Alternative heating mechanisms may be more significant during this phase, since nonthermal emission, as observed by STIX, is only detected later. STIX and AIA images reveal the presence of more compact sources of hot plasma early in the flare that originate from different locations with respect to the standard loop-top source that is observed later in the flare. However, because extended bremsstrahlung sources are much more difficult to detect than compact sources, there might be additionally heated plasma in the loop-top during hot onsets.ConclusionsThis analysis confirms the existence of “hot onsets”, with STIX detecting the hot onset pattern even earlier than GOES. These elevated temperatures imply that energy release actually begins well before any detection by STIX. Therefore, hot onsets may be significant in the initiation, early development, or even prediction of solar flares.