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arXiv 0708.2472astro-ph
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大太阳耀斑的光谱硬化

Spectral Hardening of Large Solar Flares

Paolo C. Grigis, Arnold O. Benz

摘要:

利用RHESSI观测资料,定量研究了5个大的太阳耀斑的硬X射线演化过程。来自非热电子的X射线韧致辐射的特征在于两个光谱上不同的阶段:脉冲和渐进。脉冲阶段通常由几个发射尖峰以下的软-硬-软的频谱模式,而逐渐的阶段表现为频谱硬化,而流量缓慢下降。软-硬-软(脉冲)相和硬化(逐渐)相都很好地描述了分段线性依赖的光子光谱指数的对数的硬X射线通量。该关系的不同线性部分对应于发射尖峰的不同上升和衰减阶段。的光谱的时间演化的配置和RHESSI图像中的硬X射线源的运动进行了比较。这些观测结果表明,导致这两种不同行为的电子加速的两个阶段在空间和时间上是密切相关的。冲动和渐进阶段之间的过渡被发现是平滑和渐进的,而不是突然的。这表明它们是由于共同加速器的缓慢变化而产生的,而不是由两个独立和不同的加速过程引起的。我们建议,在衰变阶段的硬化是由持续的粒子加速与更长的捕获在逃逸前的加速器。

英文摘要:

RHESSI observations are used to quantitatively study the hard X-ray evolution in 5 large solar flares selected for spectral hardening in the course of the event. The X-ray bremsstrahlung emission from non-thermal electrons is characterized by two spectroscopically distinct phases: impulsive and gradual. The impulsive phase usually consists of several emission spikes following a soft-hard-soft spectral pattern, whereas the gradual stage manifests itself as spectral hardening while the flux slowly decreases. Both the soft-hard-soft (impulsive) phase and the hardening (gradual) phase are well described by piecewise linear dependence of the photon spectral index on the logarithm of the hard X-ray flux. The different linear parts of this relation correspond to different rise and decay phases of emission spikes. The temporal evolution of the spectra is compared with the configuration and motion of the hard X-ray sources in RHESSI images. These observations reveal that the two stages of electron acceleration causing these two different behaviors are closely related in space and time. The transition between the impulsive and gradual phase is found to be smooth and progressive rather than abrupt. This suggests that they arise because of a slow change in a common accelerator rather than being caused by two independent and distinct acceleration processes. We propose that the hardening during the decay phase is caused by continuing particle acceleration with longer trapping in the accelerator before escape.

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