Magnetic Reconnection–driven Energization of Protons up to ∼400 keV at the Near-Sun Heliospheric Current Sheet

M. I. Desai, J. F. Drake, T. Phan, Z. Yin, M. Swisdak, D. J. McComas, S. D. Bale, A. Rahmati, D. Larson, W. H. Matthaeus, M. A. Dayeh, M. J. Starkey, N. E. Raouafi, D. G. Mitchell, C. M. S. Cohen, J. R. Szalay, J. Giacalone, M. E. Hill, E. R. Christian, N. A. Schwadron, R. L. McNutt, O. Malandraki, P. Whittlesey, R. Livi and J. C. Kasper
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Abstract

We report observations of direct evidence of energetic protons being accelerated above ∼400 keV within the reconnection exhaust of a heliospheric current sheet (HCS) crossing by NASA’s Parker Solar Probe (PSP) at a distance of ∼16.25 solar radii (Rs) from the Sun. Inside the exhaust, both the reconnection-generated plasma jet and the accelerated protons up to ∼400 keV propagated toward the Sun, unambiguously establishing their origin from HCS reconnection sites located antisunward of PSP. Within the core of the exhaust, PSP detected stably trapped energetic protons up to ∼400 keV, which is ≈1000 times greater than the available magnetic energy per particle. The differential energy spectrum of the accelerated protons behaved as a pure power law with spectral index of ∼−5. Supporting simulations using the kglobal model suggest that the trapping and acceleration of protons up to ∼400 keV in the reconnection exhaust are likely facilitated by merging magnetic islands with a guide field between ∼0.2 and 0.3 of the reconnecting magnetic field, consistent with the observations. These new results, enabled by PSP’s proximity to the Sun, demonstrate that magnetic reconnection in the HCS is a significant new source of energetic particles in the near-Sun solar wind. Our findings of in situ particle acceleration via magnetic reconnection at the HCS provide valuable insights into this fundamental process, which frequently converts the large magnetic field energy density in the near-Sun plasma environment and may be responsible for heating the Sun’s atmosphere, accelerating the solar wind, and energizing charged particles to extremely high energies in solar flares.
在近太阳日球层电流片上,磁重联驱动的质子能量高达~ 400 keV
我们报告了美国宇航局帕克太阳探测器(PSP)在距离太阳约16.25太阳半径(Rs)处穿越日球层电流片(HCS)的重联排放中高能质子被加速到~ 400 keV以上的直接证据。在排气内部,重联产生的等离子体射流和高达400kev的加速质子都向太阳传播,明确地确定了它们的起源是位于PSP反太阳方向的HCS重联点。在排气的核心,PSP检测到稳定捕获的高能质子高达~ 400 keV,这是每个粒子可用磁能的≈1000倍。加速质子的微分能谱表现为纯幂律,谱指数为~−5。使用kglobal模型进行的支持性模拟表明,重联排气中高达~ 400kev的质子被捕获和加速可能是由磁岛合并而成的,磁岛的引导场介于重联磁场的~ 0.2和0.3之间,这与观测结果一致。这些新的结果,由于PSP靠近太阳,证明了HCS中的磁重联是近太阳太阳风中高能粒子的重要新来源。我们在HCS通过磁重联的原位粒子加速的发现为这一基本过程提供了有价值的见解,该过程经常转换近太阳等离子体环境中的大磁场能量密度,并可能负责加热太阳大气,加速太阳风,并使带电粒子在太阳耀斑中获得极高能量。
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