An Unusual Energetic Particle Flux Enhancement Associated with Solar Wind Magnetic Island Dynamics
An Unusual Energetic Particle Flux Enhancement Associated with Solar Wind Magnetic Island Dynamics
复制标题
DOI：
10.3847/2041-8213/aaddf6
复制
发表时间：
2018-09
期刊：
影响因子：
--
通讯作者：
L.-L. Zhao-L.;G. Zank;O. Khabarova;S. Du;Y. Chen;L. Adhikari;Q. Hu
中科院分区：
文献类型：
--
作者：
L.-L. Zhao-L.;G. Zank;O. Khabarova;S. Du;Y. Chen;L. Adhikari;Q. Hu
在超音速太阳风中，带电粒子在小尺度相互作用的磁通量绳“海洋”中被统计加速的可能性越来越受到人们的信任。在这封信中，我们扩展了Zank等人的统计输运理论的近同位素粒子分布，包括一个逃逸项对应的粒子损失从一个有限的加速区域。稳态一维解的加速粒子的速度分布函数和微分强度。我们展示了一个高能粒子通量增强事件下游的冲击附近的5 Au，这是不一致的经典扩散冲击加速（DSA）的预测，但可以解释与磁岛的局部加速的观测。一个自动化的梯度Shafranov重建方法来识别小规模的磁通量绳背后的冲击。第一次，观测到的高能粒子的“时间-强度”的轮廓和光谱与理论预测进行了定量比较。结果表明，相互作用磁岛的随机加速成功地解释了所观察到的：（i）粒子强度峰值出现在激波后，而不是象标准DSA预测的那样出现在激波前沿;（ii）粒子通量放大因子随粒子能量的增加而增加;（ii）粒子强度峰值与激波前沿之间的距离随能量的增加而增加;和（iv）硬化的粒子幂律谱随着距离下游的冲击波。
The possibility that charged particles are accelerated statistically in a “sea” of small-scale interacting magnetic flux ropes in the supersonic solar wind is gaining credence. In this Letter, we extend the Zank et al. statistical transport theory for a nearly isotopic particle distribution by including an escape term corresponding to particle loss from a finite acceleration region. Steady-state 1D solutions for both the accelerated particle velocity distribution function and differential intensity are derived. We show Ulysses observations of an energetic particle flux enhancement event downstream of a shock near 5 au that is inconsistent with the predictions of classical diffusive shock acceleration (DSA) but may be explained by local acceleration associated with magnetic islands. An automated Grad-Shafranov reconstruction approach is employed to identify small-scale magnetic flux ropes behind the shock. For the first time, the observed energetic particle “time-intensity” profile and spectra are quantitatively compared with theoretical predictions. The results show that stochastic acceleration by interacting magnetic islands accounts successfully for the observed (i) peaking of particle intensities behind the shock instead of at the shock front as standard DSA predicts; (ii) increase in the particle flux amplification factor with increasing particle energy; (ii) increase in distance between the particle intensity peak and the shock front with increasing energy; and (iv) hardening of particle power-law spectra with increasing distance downstream of the shock.