CME-driven Shock and Type II Solar Radio Burst Band Splitting
CME-driven Shock and Type II Solar Radio Burst Band Splitting
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DOI：
10.3847/1538-4357/aae9e5
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发表时间：
2018-10
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影响因子：
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通讯作者：
N. Chrysaphi;E. P. Kontar;G. Holman;M. Temmer
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文献类型：
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作者：
N. Chrysaphi;E. P. Kontar;G. Holman;M. Temmer
日冕物质抛射（cme）被认为是在日冕和行星际空间产生冲击的有效方法。激波和激波加速的一个重要特征是II型太阳射电暴，它随激波速度漂移，并产生基频和高谐波等离子体射电发射带。II型射电暴的一个有趣的方面是偶尔会将谐波带分裂成更薄的通道，称为带分裂。在这里，我们报告了cme驱动的激波在II型爆发中产生能带分裂的详细成像和光谱观察。利用LOFAR，我们研究了II型爆发与相关CME事件的时空关系，使用源成像来计算视日冕密度，并演示了如何使用源成像来估计投影效果。我们考虑了两种被广泛接受的能带分裂模型，它们对相对于激波锋面的真实发射源的位置做出了相反的预测。我们的观察表明，上下子带源的位置在空间上的间隔为~ 0.2±0.05 R⊙。然而，我们第一次定量地表明，这种分离与等离子体射电发射的单一区域的无线电波散射一致，这意味着分带II型源可能来自几乎同空间的位置。考虑到散射的影响，观测结果为该模型提供了支持证据，该模型将能带分裂解释为源自激波锋面上游和下游区域的发射，这两个区域实际上是共空间区域。
Coronal mass ejections (CMEs) are believed to be effective in producing shocks in the solar corona and interplanetary space. One of the important signatures of shocks and shock acceleration are Type II solar radio bursts that drift with the shock speed and produce bands of fundamental and higher harmonic plasma radio emission. An intriguing aspect of Type II radio bursts is the occasional split of a harmonic band into thinner lanes, known as band splitting. Here we report a detailed imaging and spectroscopic observation of a CME-driven shock producing band splitting in a Type II burst. Using LOFAR, we examine the spatial and temporal relation of the Type II burst to the associated CME event, use source imaging to calculate the apparent coronal density, and demonstrate how source imaging can be used to estimate projection effects. We consider two widely accepted band-splitting models that make opposing predictions regarding the locations of the true emission sources with respect to the shock front. Our observations suggest that the locations of the upper and lower subband sources are spatially separated by ∼0.2 ± 0.05 R⊙. However, we quantitatively show, for the first time, that such separation is consistent with radio-wave scattering of plasma radio emission from a single region, implying that the split-band Type II sources could originate from nearly cospatial locations. Considering the effects of scattering, the observations provide supporting evidence for the model that interprets the band splitting as emission originating in the upstream and downstream regions of the shock front, two virtually cospatial areas.