费米-LAT揭示太阳伽马射线在太阳活动周期中的神秘变化
Puzzling Variation of Gamma Rays from the Sun over the Solar Cycle Revealed with Fermi-LAT
AI总结：
利用费米-LAT 15年数据，发现太阳伽马射线盘状成分通量随太阳活动周期正常变化，而扩展成分变化异常复杂，暗示内日球层宇宙射线输运机制或存在未知成分。
摘要：
太阳的稳态伽马射线发射被认为由两个与银河宇宙射线相互作用产生的发射成分组成：（1）强子盘状成分，和（2）轻子扩展成分，后者在太阳边缘达到峰值并延伸到日球层。这些成分的通量预计会随11年太阳活动周期而变化，在太阳活动极小期最高，在太阳活动极大期最低，因为它随宇宙射线通量而变化。目前尚无研究分析每个成分在太阳活动周期中的通量变化。在这项工作中，我们利用费米大面积望远镜15年的观测数据，测量了每个成分通量的时间变化，并将其与太阳黑子数以及来自近地AMS-02的银河宇宙射线通量进行比较。我们发现，盘状成分的通量变化与太阳黑子数呈反相关，并与宇宙射线质子相关，正如预期的那样，这证实了其发射机制。相比之下，扩展成分表现出更复杂的变化：尽管最初与太阳黑子数呈反相关，但在整个15年期间，我们既未发现其与太阳黑子数的反相关，也未发现其与宇宙射线电子的相关性。这很可能表明，内日球层中的宇宙射线输运和调制出乎意料地复杂，并且可能对电子和质子有所不同，或者，存在一个额外的、未知的伽马射线或宇宙射线成分。这些发现对空间天气研究产生影响，并强调了对第25太阳活动周期及正在进行的极性反转进行密切监测的必要性。
英文摘要：
The steady-state gamma-ray emission from the Sun is thought to consist of two emission components due to interactions with Galactic cosmic rays: (1) a hadronic disk component, and (2) a leptonic extended component peaking at the solar edge and extending into the heliosphere. The flux of these components is expected to vary with the 11-year solar cycle, being highest during solar minimum and lowest during solar maximum, as it varies with the cosmic-ray flux. No study has yet analyzed the flux variation of each component over solar cycles. In this work, we measure the temporal variations of the flux of each component over 15 years of Fermi Large Area Telescope observations and compare them with the sunspot number and Galactic cosmic-ray flux from AMS-02 near Earth. We find that the flux variation of the disk anticorrelates with the sunspot number and correlates with cosmic-ray protons, as expected, confirming its emission mechanism. In contrast, the extended component exhibits a more complex variation: despite an initial anticorrelation with the sunspot number, we find neither anticorrelation with the sunspot number nor correlation with cosmic-ray electrons over the full 15-year period. This most likely suggests that cosmic-ray transport and modulation in the inner heliosphere are unexpectedly complex and may differ for electrons and protons or, alternatively, that there is an additional, unknown component of gamma rays or cosmic rays. These findings impact space weather research and emphasize the need for close monitoring of Cycle 25 and the ongoing polarity reversal.
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