The frequency ratio and time delay of solar radio emissions with fundamental and harmonic components
The frequency ratio and time delay of solar radio emissions with fundamental and harmonic components
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具有基波和谐波分量的太阳射电发射的频率比和时延
DOI：
10.1093/mnras/stad325
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发表时间：
2023
影响因子：
4.8
通讯作者：
Chen X
中科院分区：
文献类型：
--
作者：
Chen X
通过等离子体发射机制产生的太阳射电爆发产生接近本地等离子体频率的辐射（基波发射）和等离子体频率的两倍（谐波）。虽然这两个频率的理论比值接近2，但同时观测得到的比值范围从1.6到2，这表明比值不是2，基本发射的延迟，或者两者兼而有之。为了解决这个长期存在的问题，我们进行了高频率，高时间分辨率成像光谱的III型和J型爆发与精细结构的基波和谐波分量与LOFAR之间的30和80 MHz。在基频和谐波频率下同时观察到的短寿命和窄频带精细结构给出了1.66和1.73的频率比，与以前的观测结果相似。然而，频率-时间互相关表明，频率比为1.99和1.95，F和H发射之间的时间延迟为1.00和1.67秒，分别为每个事件。因此，不同于2的同时频率比测量是由基波发射的延迟引起的。在引起基本发射延迟的过程中，各向异性无线电波散射是主要的。此外，再现延迟的基本排放的各向异性和密度波动的水平是一致的，所需的模拟源的大小和持续时间的基本排放。使用这些模拟，我们能够，第一次，提供定量估计的延迟时间的基本发射所造成的无线电波传播效应在多个频率，这可以用于未来的研究。
Solar radio bursts generated through the plasma emission mechanism produce radiation near the local plasma frequency (fundamental emission) and double the plasma frequency (harmonic). While the theoretical ratio of these two frequencies is close to 2, simultaneous observations give ratios ranging from 1.6 to 2, suggesting either a ratio different from 2, a delay of the fundamental emission, or both. To address this long-standing question, we conducted high-frequency, high-time resolution imaging spectroscopy of type III and type J bursts with fine structures for both the fundamental and harmonic components with LOFAR between 30 and 80 MHz. The short-lived and narrow frequency-band fine structures observed simultaneously at fundamental and harmonic frequencies give a frequency ratio of 1.66 and 1.73, similar to previous observations. However, frequency-time cross-correlations suggest a frequency ratio of 1.99 and 1.95 with a time delay between the F and H emissions of 1.00 and 1.67 s, respectively for each event. Hence, simultaneous frequency ratio measurements different from 2 are caused by the delay of the fundamental emission. Among the processes causing fundamental emission delays, anisotropic radio-wave scattering is dominant. Moreover, the levels of anisotropy and density fluctuations reproducing the delay of fundamental emissions are consistent with those required to simulate the source size and duration of fundamental emissions. Using these simulations we are able to, for the first time, provide quantitative estimates of the delay time of the fundamental emissions caused by radio-wave propagation effects at multiple frequencies, which can be used in future studies.