First Frequency-time-resolved Imaging Spectroscopy Observations of Solar Radio Spikes
First Frequency-time-resolved Imaging Spectroscopy Observations of Solar Radio Spikes
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DOI：
10.3847/2041-8213/ac1a7d
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发表时间：
2021-08
期刊：
影响因子：
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通讯作者：
D. L. Clarkson;E. P. Kontar;M. Gordovskyy;N. Chrysaphi;N. Vilmer
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文献类型：
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作者：
D. L. Clarkson;E. P. Kontar;M. Gordovskyy;N. Chrysaphi;N. Vilmer
在GHz ~数十MHz范围内观测到的动态光谱中，太阳射电尖峰是持续时间短、带宽窄的精细结构。它们非常短的持续时间和狭窄的频率带宽表明太阳日冕中亚秒级的小规模能量释放，但它们的起源尚不清楚。利用低频阵列，我们展示了与日冕物质抛射相关的单个无线电尖峰的空间、频率和时间分辨观测。单个射电尖峰成像表明，观测面积随时间的推移而增加，单个尖峰的质心位置与太阳翼平行移动。与在同一事件中观测到的单个IIIb型条纹的峰特性比较，发现在持续时间、带宽、漂移速率、极化和观测面积上都有相似之处，并且在像面上的峰和条纹运动表明基本等离子体发射，峰发射区域约为~ 108 cm，亮度温度高达1013 K。观测到的单个尖峰爆发的空间、光谱和时间特性也暗示了导致尖峰在闭环结构中通过各向异性密度湍流逃逸的辐射，这些结构的散射优先沿着平行于散射区边缘的引导磁场方向进行。在观测到的时间剖面上，散射的优势表明能量释放时间可能比通常假设的要短。观测结果还表明，沿闭合磁力线的密度湍流各向异性高于沿开放磁力线的密度湍流各向异性。
Solar radio spikes are short duration and narrow bandwidth fine structures in dynamic spectra observed from the GHz to tens of MHz range. Their very short duration and narrow frequency bandwidth are indicative of subsecond small-scale energy release in the solar corona, yet their origin is not understood. Using the LOw Frequency ARray, we present spatially, frequency, and time resolved observations of individual radio spikes associated with a coronal mass ejection. Individual radio spike imaging demonstrates that the observed area is increasing in time and the centroid positions of the individual spikes move superluminally parallel to the solar limb. Comparison of spike characteristics with that of individual Type IIIb striae observed in the same event show similarities in duration, bandwidth, drift rate, polarization, and observed area, as well the spike and striae motion in the image plane suggesting fundamental plasma emission with the spike emission region on the order of ∼108 cm, with brightness temperature as high as 1013 K. The observed spatial, spectral, and temporal properties of the individual spike bursts are also suggestive of the radiation responsible for spikes escaping through anisotropic density turbulence in closed loop structures with scattering preferentially along the guiding magnetic field oriented parallel to the limb in the scattering region. The dominance of scattering on the observed time profile suggests the energy release time is likely to be shorter than what is often assumed. The observations also imply that the density turbulence anisotropy along closed magnetic field lines is higher than along open field lines.