Electron acceleration and radio emission following the early interaction of two coronal mass ejections
Electron acceleration and radio emission following the early interaction of two coronal mass ejections
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DOI：
10.1051/0004-6361/202038801
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发表时间：
2020-08
影响因子：
6.5
通讯作者：
D. Morosan;E. Palmerio;J. Räsänen;E. Kilpua;J. Magdalenić;B. Lynch;A. Kumari;J. Pomoell;M. Palmroth
中科院分区：
文献类型：
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作者：
D. Morosan;E. Palmerio;J. Räsänen;E. Kilpua;J. Magdalenić;B. Lynch;A. Kumari;J. Pomoell;M. Palmroth
语境。日冕物质抛射（CME）是太阳磁化等离子体的大规模喷发，通常伴随着加速电子产生的太阳射电爆发。目标。加速电子束的强大来源是日冕物质抛射驱动的激波，但是，还有其他机制能够在日冕物质抛射期间加速电子。到目前为止，研究主要基于太阳射电爆发的形状和动态光谱特征，将太阳射电爆发分为五组（I-V型）。在这里，我们的目标是确定与日冕物质抛射相关的移动射电爆发的起源，这些射电爆发不符合目前太阳射电发射的分类。方法。通过使用 Nançay 射电日照仪的射电成像，结合太阳动力学观测站、太阳和日光层观测站以及日地关系观测站航天器的观测，我们研究了 2013 年 5 月 22 日伴随两次日冕物质抛射发生的移动射电爆发。我们使用两次相关日冕物质抛射的三维重建来显示观测到的射电发射的可能来源。结果。我们在日冕中异常高的高度发现了三个移动射电暴，它们位于日冕物质抛射的北侧，并与日冕物质抛射同步向外移动。射电爆发对应于动态频谱中持续时间约为 1 秒的精细结构发射，并且它们可能表现出正向或反向频率漂移。由于日冕物质抛射紧随早期日冕物质抛射而扩展，日冕物质抛射-日冕物质抛射的低相互作用可能是观测到的射电发射的原因。结论。我们首次报告了新型短持续时间爆发的存在，这是电子束在日冕物质抛射侧面加速的特征。源自同一区域并以相似方向传播的两个后续日冕物质抛射提供了复杂的环境磁场配置和创建塌缩磁陷阱的有利条件。如果日冕物质抛射驱动的波（例如冲击波）可能与周围的磁场线相交两次，就会形成这些陷阱。因此，电子将在这些交叉点处创建的镜像点处进一步加速，并最终逸出，产生具有正向和反向漂移的等离子体发射脉冲。
Context. Coronal mass ejections (CMEs) are large eruptions of magnetised plasma from the Sun that are often accompanied by solar radio bursts produced by accelerated electrons. Aims. A powerful source for accelerating electron beams are CME-driven shocks, however, there are other mechanisms capable of accelerating electrons during a CME eruption. So far, studies have relied on the traditional classification of solar radio bursts into five groups (Type I–V) based mainly on their shapes and characteristics in dynamic spectra. Here, we aim to determine the origin of moving radio bursts associated with a CME that do not fit into the present classification of the solar radio emission. Methods. By using radio imaging from the Nançay Radioheliograph, combined with observations from the Solar Dynamics Observatory, Solar and Heliospheric Observatory, and Solar Terrestrial Relations Observatory spacecraft, we investigate the moving radio bursts accompanying two subsequent CMEs on 22 May 2013. We use three-dimensional reconstructions of the two associated CME eruptions to show the possible origin of the observed radio emission. Results. We identified three moving radio bursts at unusually high altitudes in the corona that are located at the northern CME flank and move outwards synchronously with the CME. The radio bursts correspond to fine-structured emission in dynamic spectra with durations of ∼1 s, and they may show forward or reverse frequency drifts. Since the CME expands closely following an earlier CME, a low coronal CME–CME interaction is likely responsible for the observed radio emission. Conclusions. For the first time, we report the existence of new types of short duration bursts, which are signatures of electron beams accelerated at the CME flank. Two subsequent CMEs originating from the same region and propagating in similar directions provide a complex configuration of the ambient magnetic field and favourable conditions for the creation of collapsing magnetic traps. These traps are formed if a CME-driven wave, such as a shock wave, is likely to intersect surrounding magnetic field lines twice. Electrons will thus be further accelerated at the mirror points created at these intersections and eventually escape to produce bursts of plasma emission with forward and reverse drifts.