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arXiv 1001.1464astro-ph.SRastro-ph.HE
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小太阳活动区偏离幂律耀斑尺寸分布的证据

Evidence for departure from a power-law flare size distribution for a small solar active region

M. S. Wheatland

摘要:

活动区11029是在太阳活动极低的时候观测到的一个小的、高度产生耀斑的太阳活动区。该区域只产生了小规模耀斑:$>70$地球静止观测环境卫星为该区域发生的最大的一次事件的1- $8Å$通量峰值为$2.2\times 10^{-6} {\rm W} {\rm m}^{-2}$(地球静止观测环境卫星C2.2)。减去背景的GOES峰值通量分布表明偏离了高于$10^{-6} {\rm W} {\rm m}^{-2}$的幂律行为,贝叶斯模型比较强烈支持幂律加翻转模型的分布,而不是简单的幂律模型。偏离幂律的原因是这个小的活性区域具有有限的能量。该区域的耀斑速率随时间而变化,在光球磁场复杂性开始增加的两天内变得非常高。观察到的事件的等待时间分布是一致的分段常数泊松模型。这些结果对耀斑统计模型和太阳活动区能量平衡模型提出了挑战。

英文摘要:

Active region 11029 was a small, highly flare-productive solar active region observed at a time of extremely low solar activity. The region produced only small flares: the largest of the $>70$ Geostationary Observational Environmental Satellite (GOES) events for the region has a peak 1--$8Å$ flux of $2.2\times 10^{-6} {\rm W} {\rm m}^{-2}$ (GOES C2.2). The background-subtracted GOES peak-flux distribution suggests departure from power-law behavior above $10^{-6} {\rm W} {\rm m}^{-2}$, and a Bayesian model comparison strongly favors a power-law plus rollover model for the distribution over a simple power-law model. The departure from the power law is attributed to this small active region having a finite amount of energy. The rate of flaring in the region varies with time, becoming very high for two days coinciding with the onset of an increase in complexity of the photospheric magnetic field. The observed waiting-time distribution for events is consistent with a piecewise-constant Poisson model. These results present challenges for models of flare statistics and of energy balance in solar active regions.

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