两个临近脉冲型太阳能量电子事件的观测与拟合

Observations and Fitting of Two Adjacent Impulsive Solar Energetic Electrons Events

WIND飞船在2010年11月15日观测到两个临近的脉冲型太阳能量电子事件,这两个事件在1 AU处呈现出不同类型的通量-时间曲线.事件一的通量表现出快速上升及快速下降的特性;事件二则表现为缓慢上升,更缓慢下降,事件二的持续时间是事件一的5~17倍.以往的解释认为事件二中的电子在行星际受到了更强的散射.本文引入等腰三角形的释放函数并求解电报方程,利用得到的解对1 AU处的观测进行拟合.根据最佳拟合结果反推两事件在太阳上的释放函数和在行星际传播的平均自由程,发现造成两事件在1 AU处能谱和通量时间曲线形状不同的原因是太阳上电子加速过程的不同而非行星际散射.结合SOHO卫星的白光观测,发现两事件可能与一个CME(日冕物质抛射)相关,并进一步推测了这两个太阳电子事件可能的加速图像.

Two adjacent impulsive Solar Energetic Electron(SEE) events were observed by WIND/3DP on November 15,2010.The temporal profiles of the two events exhibit different behaviors:Even-11 shows a rapid rise and rapid decay temporal profile,while Event 2 shows a slow rise and very slow decay temporal profile with a duration 5~17 times longer than the duration of Event 1.Based on previous studies,Event 2 should have experienced much stronger scattering in the Interplanetary Medium(IPM),compared with Event 1.However,the similar strongly anisotropic pitch-angle distributions of the two events observed at 1 AU suggest the same weak scattering in the IPM(especially near 1 AU).On the other hand,Event 2 has harder peak flux versus energy spectrum than Event 1.Using the telegraph equation with an isosceles-triangle injection function of time,the solar source and interplanetary propagation of these electrons are investigated and then the electron injection profile at the Sun and the electron mean free path in the IPM are obtained from the best-fit to in-situ observations.In Event 1,the solar injection of low-energy(high-energy) electrons starts at14:14±00:04UT(14:36±00:01 UT) and lasts for about 50 minutes(about 7 minutes).In Event 2,the solar injection of low-energy(high-energy) electrons starts at 14:34±00:13UT(14:25±00:02UT)and lasts for about 170 minutes(about 90 minutes).For both events,the electron energy spectrum during the electron solar injection does not become harder(continuously) with increasing time,suggesting the absence of electron storage in the corona(after acceleration).The inferred electron mean free path in the IPM is larger than that at 1 AU for both events.These results suggest that for the two events,the different energy spectra and temporal profiles observed at 1 AU were resulted from the electron acceleration at the Sun,not from the propagation effects in the IPM.By comparing the inferred electron injection times with GOES SXR and SOHO white light observations,these two events are likely associated with a CME.