Statistics of “Cold” Early Impulsive Solar Flares in X-Ray and Microwave Domains
Statistics of “Cold” Early Impulsive Solar Flares in X-Ray and Microwave Domains
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DOI：
10.3847/1538-4357/aab271
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发表时间：
2018-02
期刊：
影响因子：
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通讯作者：
A. Lysenko;A. Altyntsev;N. Meshalkina;D. Zhdanov;G. Fleishman
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作者：
A. Lysenko;A. Altyntsev;N. Meshalkina;D. Zhdanov;G. Fleishman
太阳耀斑通常发生在预耀斑/预热阶段之后，这一阶段几乎或完全是热的。相反，有所谓的早期脉冲耀斑，没有表现出（显著的）耀斑前加热，而是经常表现出Neupert效应——一种关系，即脉冲阶段之后是一个渐进的、累积的热响应。这被解释为在脉冲阶段非热能释放占主导地位，尽管如果在脉冲阶段释放的热能和非热能数量相当，预计会出现类似的现象。然而，一些耀斑在非热电子能量输入和等离子体加热之间确实表现出很好的定量对应关系；在这种情况下，热响应很弱，这导致它们被称为“冷”耀斑。我们对1994年11月至2017年4月期间Konus-Wind仪器记录的触发模式下的早期脉冲耀斑进行了系统搜索，并根据硬x射线（HXR） （Konus-Wind）和软x射线（地球静止运行环境卫星）发射的关系选择了27个冷耀斑。对于这些事件，我们收集了来自不同仪器的所有可用微波数据。我们获得了事件的HXR和微波发射的时间和光谱参数，并检验了它们之间的相关性。我们发现，与“平均”耀斑相比，冷耀斑：(i)在x射线域中更弱、更短、更硬；（ii）更硬、更短，但在微波中不会变弱；（iii）在微波中具有明显更高的光谱峰值频率。我们讨论了这些区别的可能的物理原因和这一发现的含义。
Solar flares often happen after a preflare/preheating phase, which is almost or entirely thermal. In contrast, there are the so-called early impulsive flares that do not show a (significant) preflare heating, but instead often show the Neupert effect—a relationship where the impulsive phase is followed by a gradual, cumulative-like, thermal response. This has been interpreted as a dominance of nonthermal energy release at the impulsive phase, even though a similar phenomenology is expected if the thermal and nonthermal energies are released in comparable amounts at the impulsive phase. Nevertheless, some flares do show a good quantitative correspondence between the nonthermal electron energy input and plasma heating; in such cases, the thermal response was weak, which results in them being called “cold” flares. We undertook a systematic search for such events among early impulsive flares registered by the Konus-Wind instrument in the triggered mode from 11/1994 to 4/2017, and selected 27 cold flares based on relationships between hard X-ray (HXR) (Konus-Wind) and soft X-ray (Geostationary Operational Environmental Satellite) emission. For these events, we put together all available microwave data from different instruments. We obtained temporal and spectral parameters of HXR and microwave emissions of the events and examined correlations between them. We found that, compared to a “mean” flare, the cold flares: (i) are weaker, shorter, and harder in the X-ray domain; (ii) are harder and shorter, but not weaker in the microwaves; (iii) have a significantly higher spectral peak frequencies in the microwaves. We discuss the possible physical reasons for these distinctions and implication of the finding.