arXiv 1508.010652015-08-05astro-ph.SR

日冕中双向电子束的低频射电观测

Low frequency radio observations of bi-directional electron beams in the solar corona

Eoin P. Carley, Hamish Reid, Nicole Vilmer, Peter T. Gallagher

DOI：: 10.1051/0004-6361/201526251

摘要：

穿过日冕的冲击波的无线电信号被称为II型太阳射电爆发。在极少数情况下，这些爆发可以表现出被称为"人字形"的精细结构，这是在冲击波前沿发生的粒子加速的直接指示。然而，很少有研究已经进行人字形和底层粒子加速过程的细节是未知的。在这里，我们使用一种图像处理技术，称为霍夫变换的统计分析的人字形精细结构的射电爆发在$\sim$ 20 - 90 MHz的罗斯日地观测站于2011年9月22日。我们确定了188个单独的爆发，这是双向电子束的签名不断加速到0.16 $_{-0.10}^{+0.11} c$的速度。这种情况发生在冲击加速地点，最初位于日冕中的恒定高度$\sim$ 0.6 R $_{\odot}$，然后转变为$\sim$ 0.5 R $_{\odot}$。反向阳光束行进距离为170 $_{-97}^{+174}$毫米（并可能进一步）远离加速网站，而那些朝着太阳行进来停止更快，达到一个较小的距离为112 $_{-76}^{+84}$毫米。我们表明，停止的距离为向阳光束可能取决于总的数密度和速度的光束。我们的研究得出结论，人字形精细结构的详细统计分析可以提供导致这些相对罕见的射电爆发的日冕的物理性质的信息。

英文摘要：

The radio signature of a shock travelling through the solar corona is known as a type II solar radio burst. In rare cases these bursts can exhibit a fine structure known as `herringbones', which are a direct indicator of particle acceleration occurring at the shock front. However, few studies have been performed on herringbones and the details of the underlying particle acceleration processes are unknown. Here, we use an image processing technique known as the Hough transform to statistically analyse the herringbone fine structure in a radio burst at $\sim$20-90 MHz observed from the Rosse Solar-Terrestrial Observatory on 2011 September 22. We identify 188 individual bursts which are signatures of bi-directional electron beams continuously accelerated to speeds of 0.16$_{-0.10}^{+0.11} c$. This occurs at a shock acceleration site initially at a constant altitude of $\sim$0.6 R$_{\odot}$ in the corona, followed by a shift to $\sim$0.5 R$_{\odot}$. The anti-sunward beams travel a distance of 170$_{-97}^{+174}$ Mm (and possibly further) away from the acceleration site, while those travelling toward the sun come to a stop sooner, reaching a smaller distance of 112$_{-76}^{+84}$ Mm. We show that the stopping distance for the sunward beams may depend on the total number density and the velocity of the beam. Our study concludes that a detailed statistical analysis of herringbone fine structure can provide information on the physical properties of the corona which lead to these relatively rare radio bursts.

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