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arXiv 1209.0728astro-ph.SR
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太阳耀斑早期上升阶段热能与非热能的分配

Thermal to Nonthermal Energy Partition at the Early Rise Phase of Solar Flares

Alexander A. Altyntsev, Gregory D. Fleishman, Sergey V. Lesovoi, Natalia S. Meshalkina

摘要:

在某些耀斑中,X射线波段的热分量出现得比非热分量早得多。利用敏感的微波观测,我们重新审视了Battaglia等人(2009)基于RHESSI数据分析得出的这一发现。我们已经发现,非热微波辐射产生的加速电子与至少几百keV的能量,出现早的热软X射线发射表明,电子加速发生在非常早期的耀斑阶段。因此,在耀斑的早期阶段没有探测到硬X射线是一个有限的RHESSI灵敏度的人为因素。在所有考虑的事件中,微波发射强度在早期耀斑阶段增加。我们发现,无论是热或非热的回旋同步辐射可以占主导地位的低频部分的微波光谱低于发生在3-10 GHz的光谱峰值。相比之下,光谱的高频光学薄部分总是由非热的加速电子组成,其幂律能谱在早期耀斑阶段可以扩展到几MeV。这意味着,即使在这个阶段被加速的电子的总数很小,它们的非热光谱也得到了充分的发展。这意味着可用种子粒子的加速过程是完全可操作的。虽然等离子体加热效率很高,但是这种种子群体的产生(通常称为粒子从热池“注入”到加速中的过程)在该阶段具有相当低的效率。这种加热和加速之间的不平衡(有利于加热)在大多数可用的耀斑模型中很难调和。这让人想起焦耳加热和逃逸电子加速之间的权衡,它对电子注入加速过程施加了额外的约束。

英文摘要:

In some flares the thermal component appears much earlier than the nonthermal component in X-ray range. Using sensitive microwave observations we revisit this finding made by Battaglia et al. (2009) based on RHESSI data analysis. We have found that nonthermal microwave emission produced by accelerated electrons with energy of at least several hundred keV, appears as early as the thermal soft X-ray emission indicative that the electron acceleration takes place at the very early flare phase. The non-detection of the hard X-rays at that early stage of the flares is, thus, an artifact of a limited RHESSI sensitivity. In all considered events, the microwave emission intensity increases at the early flare phase. We found that either thermal or nonthermal gyrosynchrotron emission can dominate the low-frequency part of the microwave spectrum below the spectral peak occurring at 3-10 GHz. In contrast, the high-frequency optically thin part of the spectrum is always formed by the nonthermal, accelerated electron component, whose power-law energy spectrum can extend up to a few MeV at this early flare stage. This means that even though the total number of accelerated electrons is small at this stage, their nonthermal spectrum is fully developed. This implies that an acceleration process of available seed particles is fully operational. While, creation of this seed population (the process commonly called `injection' of the particles from the thermal pool into acceleration) has a rather low efficiency at this stage, although, the plasma heating efficiency is high. This imbalance between the heating and acceleration (in favor of the heating) is difficult to reconcile within most of available flare energization models. Being reminiscent of the tradeoff between the Joule heating and runaway electron acceleration, it puts additional constraints on the electron injection into the acceleration process.

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