Fiber bursts as 3D coronal magnetic field probe in postflare loops
Fiber bursts as 3D coronal magnetic field probe in postflare loops
复制标题
光纤爆发作为后耀斑环路中的 3D 日冕磁场探针
DOI：
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发表时间：
2005
期刊：
影响因子：
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通讯作者：
A. Hofmann
中科院分区：
文献类型：
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作者：
H. Aurass;G. Rausche;G. Mann;A. Hofmann
在150···3000 MHz的频率范围内，光纤暴以连续的精细结构出现在一些复杂的太阳射电暴中。我们提出并测试了一种新的方法，利用光纤爆发作为磁场强度和后耀斑环三维场结构的探针。因此，我们假设光纤爆发是由在耀斑后回路中上升的哨声波驱动的，这些哨声波充当非热耀斑电子的磁阱。对于一个选定的事件（1997年4月07日），我们从动态无线电频谱（波茨坦）和南凯射电日光照相仪的光纤爆发成像数据中得出了光纤爆发源内的日冕磁场强度。我们利用SOHO-MDI光球场数据，将光纤爆发源位置和场强估计与外推的燃烧活跃区域NOAA 8027上方的势磁场进行了比较。光纤爆发的场强在所选的势场线子集场强的0.6至1.4倍之内，并且在不断发展的耀斑后环路中优先考虑3.5倍Newkirk （1961, ApJ, 133, 983）日冕密度模型。我们发现了独立的证据，证明在脉冲耀斑阶段后一小时的时间间隔内，考虑将选定的势场线作为耀斑后环路的拓扑和场强信息具有物理意义。我们的结论是，无线电分米和米波谱以及两个代表性频率的无线电成像足以可靠地估计（否则无法测量）耀斑后环路的日冕磁场强度。这可能是使用即将到来的FASR（频率敏捷太阳射电望远镜）仪器的重要野外探测方法。
Fiber bursts appear in some complex solar radio bursts as a continuum fine structure in the frequency range of 150 ·· ·3000 MHz. We present and test a new method to use fiber bursts as a probe of the magnetic field strength and the 3D field structure in postflare loops. Thereby we assume that fiber bursts are driven by whistler waves ascending in the postflare loops which act as magnetic traps for nonthermal flare electrons. For a selected event (1997 April 07) we derive from dynamic radio spectra (Potsdam) and Nancay Radio Heliograph imaging data of fiber bursts the coronal magnetic field strength within the fiber burst source. We compare the fiber burst source positions and field strength estimates with the extrapolated potential magnetic field above the flaring active region NOAA 8027 using SOHO-MDI photospheric field data. The field strength from fiber bursts are within a factor of 0.6 to 1.4 of the field strength of the selected subset of potential field lines and give preference to a 3.5 times Newkirk (1961, ApJ, 133, 983) coronal density model within the evolving postflare loops. We find independent proof of the physical significance of considering selected potential field lines as postflare loop field information regarding topology and field strength over a time interval of one hour after the impulsive flare phase. We conclude that radio decimeter and meter wave spectra and radio imaging at two representative frequencies are sufficient for a reliable estimate of the (otherwise not measurable) coronal magnetic field strength in postflare loops. This can be an important field sounding method using the forthcoming FASR (Frequency Agile Solar Radiotelescope) instrument.