Solar Radio Spikes and Type IIIb Striae Manifestations of Subsecond Electron Acceleration Triggered by a Coronal Mass Ejection
Solar Radio Spikes and Type IIIb Striae Manifestations of Subsecond Electron Acceleration Triggered by a Coronal Mass Ejection
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DOI：
10.3847/1538-4357/acbd3f
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发表时间：
2023-02
期刊：
影响因子：
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通讯作者：
D. L. Clarkson;E. P. Kontar;N. Vilmer;M. Gordovskyy;Xingyao Chen;N. Chrysaphi
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文献类型：
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作者：
D. L. Clarkson;E. P. Kontar;N. Vilmer;M. Gordovskyy;Xingyao Chen;N. Chrysaphi
了解亚秒尺度下与磁能释放相关的电子加速是太阳物理学的主要挑战。观测到的太阳射电尖峰是亚秒级的窄带宽爆发，Δf/f为10−3-10−2，表明电子分布的亚秒级演化。我们提出了一个统计分析的频率和时间分辨成像的个人尖峰和IIIb型条纹与日冕物质抛射（CME）。LOFAR成像显示，同颞（<2秒）尖峰和条纹强度轮廓几乎完全重叠。平均而言，这两种爆发类型具有相似的源大小，在毫秒尺度上快速扩展。在30-45 MHz范围内，射电源的质心速度通常是超光速的，与频率无关。日冕物质抛射扰乱了磁场的几何形状，导致尖峰辐射的增加，这可能是由于频繁的磁场重联。随着磁场恢复到先前的配置，观测到的天空平面发射位置在几十分钟内漂移到更高的高度。结合先前在1 GHz以上的观测结果，平均衰减时间和源大小估计值在三十年的频率上遵循1/1/f的依赖关系，类似于无线电波散射预测。在30和70 MHz之间的突发的时间和空间特性是一致的与无线电波散射具有较强的各向异性的密度波动谱。因此，无线电波发射的地点并不对应于观测到的爆发位置，这意味着在日冕物质抛射侧翼附近的加速和发射。带宽表明，在30 MHz时，固有发射源大小<1“，磁场强度比产生deconstructive尖峰的事件的平均值大两倍。
Understanding electron acceleration associated with magnetic energy release at subsecond scales presents major challenges in solar physics. Solar radio spikes observed as subsecond, narrow-bandwidth bursts with Δf/f ∼ 10−3–10−2 are indicative of a subsecond evolution of the electron distribution. We present a statistical analysis of frequency- and time-resolved imaging of individual spikes and Type IIIb striae associated with a coronal mass ejection (CME). LOFAR imaging reveals that the cotemporal (<2 s) spike and striae intensity contours almost completely overlap. On average, both burst types have a similar source size with a fast expansion at millisecond scales. The radio source centroid velocities are often superluminal and independent of frequency over 30–45 MHz. The CME perturbs the field geometry, leading to increased spike emission likely due to frequent magnetic reconnection. As the field restores itself toward the prior configuration, the observed sky-plane emission locations drift to increased heights over tens of minutes. Combined with previous observations above 1 GHz, the average decay time and source size estimates follow a ∼1/f dependence over three decades in frequency, similar to radio-wave scattering predictions. Both time and spatial characteristics of the bursts between 30 and 70 MHz are consistent with radio-wave scattering with a strong anisotropy of the density fluctuation spectrum. Consequently, the site of the radio-wave emission does not correspond to the observed burst locations and implies acceleration and emission near the CME flank. The bandwidths suggest intrinsic emission source sizes <1″ at 30 MHz and magnetic field strengths a factor of two larger than average in events that produce decameter spikes.