NARROWBAND GYROSYNCHROTRON BURSTS: PROBING ELECTRON ACCELERATION IN SOLAR FLARES
NARROWBAND GYROSYNCHROTRON BURSTS: PROBING ELECTRON ACCELERATION IN SOLAR FLARES
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DOI：
10.3847/0004-637x/826/1/38
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发表时间：
2016-05
期刊：
影响因子：
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通讯作者：
G. Fleishman;G. Nita;E. P. Kontar;D. Gary
中科院分区：
文献类型：
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作者：
G. Fleishman;G. Nita;E. P. Kontar;D. Gary
最近，在一些案例研究中，我们证明了回旋同步微波辐射可以直接从加速区检测时，捕获的电子组件是微不足道的。对于这里报道的统计研究，我们已经确定了陡峭（窄带）微波光谱的事件，这些事件没有显示出显著的捕获成分，同时显示出源均匀性的证据，这大大简化了数据分析。最初，我们确定了一个子集的20多个无线电爆发与这样的窄频谱，具有低频和高频频谱指数大于3的绝对值。陡峭的低频光谱意味着发射是非热的（对于光学厚的热发射，光谱指数不能比2更陡），并且源是相当密集和均匀的。陡峭的高频光谱意味着没有显著的电子捕获发生，否则将观察到渐进的光谱平坦化。这些射电爆发中大约有一半具有RHESSI数据，可以对源参数和演化进行详细的联合诊断。基于无线电到X射线的空间关系，定时和光谱拟合的分析，我们得出结论，在这些窄带爆发的微波发射直接源自加速区域，具有相对较强的磁场，高密度，和低温度。相比之下，热X射线发射来自一个独特的环，具有较小的磁场，较低的密度，但温度较高。因此，这些耀斑可能是由于两个（或更多）磁环之间的相互作用而发生的。
Recently, in a few case studies we demonstrated that gyrosynchrotron microwave emission can be detected directly from the acceleration region when the trapped electron component is insignificant. For the statistical study reported here, we have identified events with steep (narrowband) microwave spectra that do not show a significant trapped component and, at the same time, show evidence of source uniformity, which simplifies the data analysis greatly. Initially, we identified a subset of more than 20 radio bursts with such narrow spectra, having low- and high-frequency spectral indices larger than three in absolute value. A steep low-frequency spectrum implies that the emission is nonthermal (for optically thick thermal emission, the spectral index cannot be steeper than two), and the source is reasonably dense and uniform. A steep high-frequency spectrum implies that no significant electron trapping occurs, otherwise a progressive spectral flattening would be observed. Roughly half of these radio bursts have RHESSI data, which allow for detailed, joint diagnostics of the source parameters and evolution. Based on an analysis of radio-to-X-ray spatial relationships, timing, and spectral fits, we conclude that the microwave emission in these narrowband bursts originates directly from the acceleration regions, which have a relatively strong magnetic field, high density, and low temperature. In contrast, the thermal X-ray emission comes from a distinct loop with a smaller magnetic field, lower density, but higher temperature. Therefore, these flares likely occurred due to interaction between two (or more) magnetic loops.