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arXiv 2011.13735astro-ph.SR
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日冕中射电爆发源大小和散射的LOFAR观测

LOFAR observations of radio burst source sizes and scattering in the solar corona

Pearse C. Murphy, Eoin P. Carley, Aoife Maria Ryan, Pietro Zucca, Peter T. Gallagher

摘要:

低频无线电波的散射和折射会对日冕中观测到的射电源的大小和位置产生显著的影响。散射和折射被认为是由于湍流引起的电子密度波动。因此,确定真实的射电源大小可以提供日冕等离子体湍流的信息。然而,由于缺乏低频高空间分辨率无线电干涉观测,如低频阵列(LOFAR),很难确定真正的无线电源大小和无线电波散射水平。在这里,我们直接拟合的椭圆高斯的IIIb型射电爆发的LOFAR观测的VIVILITY,以确定其源的大小和位置。这避免了对源进行成像然后对LOFAR的点扩散函数进行去卷积的需要,去卷积会对源的大小和形状引入伪效应。对于一个34.76 MHz的爆发,我们发现沿长轴和短轴的半高全宽(FWHM)分别为$18.8^\prime$ $\pm~0.1^\prime$和$10.2^\prime$ $\pm~0.1^\prime$,在一个平面的天空日心距离为1.75 R $_\odot$。我们的研究结果表明,在太阳日冕的密度波动的水平是无线电波的散射,导致大的源尺寸的主要原因。然而,$\varepsilon$的幅度可能小于先前在捆绑阵列图像中观测无线电波散射时得出的幅度。

英文摘要:

Low frequency radio wave scattering and refraction can have a dramatic effect on the observed size and position of radio sources in the solar corona. The scattering and refraction is thought to be due to fluctuations in electron density caused by turbulence. Hence, determining the true radio source size can provide information on the turbulence in coronal plasma. However, the lack of high spatial resolution radio interferometric observations at low frequencies, such as with the LOw Frequency ARray (LOFAR), has made it difficult to determine the true radio source size and level of radio wave scattering. Here we directly fit the visibilities of a LOFAR observation of a Type IIIb radio burst with an elliptical Gaussian to determine its source size and position. This circumvents the need to image the source and then de-convolve LOFAR's point spread function, which can introduce spurious effects to the source size and shape. For a burst at 34.76 MHz, we find full width at half maximum (FWHM) heights along the major and minor axes to be $18.8^\prime$ $\pm~0.1^\prime$ and $10.2^\prime$ $\pm~0.1^\prime$, respectively, at a plane of sky heliocentric distance of 1.75 R$_\odot$. Our results suggest that the level of density fluctuations in the solar corona is the main cause of the scattering of radio waves, resulting in large source sizes. However, the magnitude of $\varepsilon$ may be smaller than what has been previously derived in observations of radio wave scattering in tied-array images.

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