Shock-excited radio burst from reconnection outflow jet?
Shock-excited radio burst from reconnection outflow jet?
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DOI：
10.1051/0004-6361:20011735
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发表时间：
2002-03
影响因子：
6.5
通讯作者：
H. Aurass;B. Vršnak;G. Mann
中科院分区：
文献类型：
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作者：
H. Aurass;B. Vršnak;G. Mann
动态（双带，拱廊）耀斑模型涉及到一个系统的形成，站在慢，也可能是快模式的冲击波与快速重联过程下爆发的灯丝。这些冲击在理论上是可以预料到的，但并没有得到观测的明确证实。在本文中，我们确定了第一次的无线电签名的快模式流出终止冲击的动态无线电爆发频谱图。站立快模式冲击揭示了零漂移II型突发记录之间的300和400兆赫。它开始于1997年4月7日耀斑脉冲相之后约1小时，持续时间超过30分钟，具有特征性的人字形精细结构和（10 ′ 6）%的带裂。没有观察到基谐模式，我们认为，该功能是基模发射。同时成像观测（Ha，Yohkoh SXT，SOHO EIT）显示了一个轻松的postflare环拱廊与明亮的软X射线尖点通常被解释为一个典型的重联模式。研究了终端激波的形成条件和射电激发条件。在重联外流中无线电探测终止激波的有利条件是扩散区的高度比较大，慢激波上游的等离子体与磁压力比β较低，以及重联磁力线之间的夹角较小。最后，我们讨论了为什么没有更频繁地观察到类似的无线电签名，以及为什么它出现得这么晚。我们强调的影响，并指出一些不一致，这可能是一个后果，通常实行特设的理想化模型的结果，以现实条件下的应用。
Models of dynamic (two-ribbon-, arcade) flares involve the formation of a system of standing slow and possibly also fast mode shock waves associated with the fast reconnection process below the erupting filament. These shocks are anticipated theoretically, but are not unambiguously confirmed by observations. In this paper we identify for the first time the radio signature of a fast mode outflow termination shock in a dynamic radio burst spectrogram. The standing fast mode shock is revealed by a zero-drift type II burst recorded between 300 and 400 MHz. It started almost 1 hour after the impulsive phase of the 7 April 1997 flare and lasted for more than 30 min. The burst shows a characteristic herringbone fine structure and a band split of (10 ′ 6)% of the emission frequency. No fundamental-harmonic pattern was observed, and we argue that the feature is fundamental mode emission. Simultaneous imaging observations (Ha, Yohkoh SXT, SOHO EIT) show a relaxed postflare loop arcade with a bright soft X-ray cusp commonly interpreted as a typical reconnection pattern. Conditions for termination shock formation and excitation of radio emision are investigated. Favourable circumstances for the radio detection of a termination shock in the reconnection outflow are a comparatively large height of the diffusion region, a low plasma to magnetic pressure ratio β upstream of the slow shocks, and a small angle between the reconnecting field lines. Finally, we discuss why similar radio signatures are not observed more frequently, and why it appeared so late in the event. We stress the implications and point to some inconsistencies which might be a consequence of commonly practiced ad hoc application of idealized model results to realistic conditions.