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arXiv 2102.00974astro-ph.SR
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莱曼α辐射观测的太阳耀斑引起的太阳辐照度变化

Solar Irradiance Variability Due To Solar Flares Observed in Lyman-alpha Emission

Ryan O. Milligan

摘要:

由于中性氢的莱曼-α(Lya)线是太阳光谱中最亮的发射线,由于非常高的背景,检测由于在该波长处的太阳耀斑引起的辐照度增加可能是具有挑战性的。以前专注于最大耀斑的研究表明,即使在这些极端情况下,Lya也只比背景高出几个百分点。在这项研究中,对约8500个大于B1级的耀斑进行了叠加历元分析,以确定耀斑对太阳EUV辐照度变化的贡献。以1-8A的X射线辐射峰值为基准时间,对GOES-15上的EUV传感器在Lya辐射中观测到的3123个B级和4972个C级耀斑的时间序列进行平均,以减小背景起伏,改善耀斑信号。这些较弱的事件的总和表明,它们产生了0.1-0.3%的太阳Lya辐照度的增强。为了进行平均比较,将相同的技术应用于453个M级和31个X级耀斑,导致Lya排放增加1-4%。耀斑也被平均相对于他们的日射角调查任何潜在的中心到边缘的变化。对于每个GOES类,在耀斑峰值的Lya的相对增强被发现减少耀斑发生更接近太阳的边缘,由于线的不透明性,和/或缩短的足迹。研究中包括的一个中等事件,C6.6耀斑,表现出异常高的Lya增加7%,可能归因于灯丝喷发失败。迄今为止,这种量级的增加只与少数X级耀斑有关。

英文摘要:

As the Lyman-alpha (Lya) line of neutral hydrogen is the brightest emission line in the solar spectrum, detecting increases in irradiance due to solar flares at this wavelength can be challenging due to the very high background. Previous studies that have focused on the largest flares have shown that even these extreme cases generate enhancements in Lya of only a few percent above the background. In this study, a superposed-epoch analysis was performed on ~8500 flares greater than B1 class to determine the contribution that flares make to changes in the solar EUV irradiance. Using the peak of the 1-8A X-ray emission as a fiducial time, the corresponding time series of 3123 B- and 4972 C-class flares observed in Lya emission by the EUV Sensor on GOES-15 were averaged to reduce background fluctuations and improve the flare signal. The summation of these weaker events showed that they produced a 0.1-0.3% enhancement to the solar Lya irradiance. For comparison on average, the same technique was applied to 453 M- and 31 X-class flares, which resulted in a 1-4% increase in Lya emission. Flares were also averaged with respect to their heliographic angle to investigate any potential center-to-limb variation. For each GOES class, the relative enhancement in Lya at the flare peak was found to diminish for flares that occurred closer to the solar limb due to the opacity of the line, and/or foreshortening of the footpoints. One modest event included in the study, a C6.6 flare, exhibited an unusually high increase in Lya of 7% that may have been attributed to a failed filament eruption. Increases of this magnitude have hitherto only been associated with a small number of X-class flares.

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