1. Purple Mountain Observatory, Chinese Academy of Sciences, Nanjing 210023;2. Key Laboratory of Dark Matter and Space Astronomy, Chinese Academy of Sciences, Nanjing 210023;3. School of Astronomy and Space Science, University of Science and Technology of China, Hefei 230026;
Neupert效应的定性描述是耀斑中脉冲分量(硬X射线、微波暴)与渐变分量(软X射线发射)之间存在的因果关系, 即耀斑最初的能量是以加速粒子的形式释放, 加 速的电子在大气传输过程中产生非热硬X射线轫致辐射, 并加热大气, 耀斑软X射线发射是 高能粒子注入大气的响应. 根据经典Neupert效应的定量描述, 硬X射线发射(表征非热 电子注入)结束时软X射线应该立刻达到极大, 但以往的观测发现一些耀斑软X射线峰值时 间($t_2$)明显晚于硬X射线结束时间($t_1$) (tau = $t_2$--$t_1, \tau > 0$), 热与非热辐射之间存在明显的偏离 经典Neupert效应的情况. 为了研究偏离经典Neupert效应的事件, 在2002---2015年 间的RHESSI (Reuven Ramaty High Energy Solar Spectroscopic Imager)和GOES (Geostationary Operational Environmental Satellites)耀斑列表中, 按照在25--50keV范围内光变较简单、软X射线有对应发射峰等判据, 共选择276个耀斑样本, 统计了这些耀斑的tau分布、环长d (用双足点源之间的距 离来表征)与tau的关系. 结果显示: (1)有227个耀斑$\tau > 0$, 即有约82%的耀斑偏离经 典Neupert效应; (2) tau$与d$之间存在一定的线性相关, 即环越长, 软X射线极大的时间越延 后; (3)似乎存在一个临界距离, 当环长小于临界距离时, 经典Neupert效应成立. 这些 结果印证了修正Neupert效应的必要性, 并对其物理意义进行了讨论.
The qualitative description of the Neupert effect is that there is a causal relationship between the pulse component (hard X-ray, microwave burst) and the gradual component (soft X-ray emission) in a flare. The initial energy of the flare is released in the form of accelerating particles. The energetic particles produce HXR (hard X-ray) via nonthermal electron-ion bremsstrahlung as they lose their energies in the chromosphere. The SXR (soft X-ray) emission of the flare is the response of energetic particles injected into the chromosphere. According to the quantitative description of the classic Neupert effect, SXR should reach maximum instantly at the end of HXR emission (sign of nonthermal electron injection). However, previous observations have found that for quite a number of flares the SXR peak time ($t_2$) is significantly later than the end time of HXR ($t_1$) ($\tau = t_2-t_1, \tau > 0$), deviating from the classic Neupert effect. In order to study the events deviating from the classic Neupert effect or not, we checked the RHESSI (Reuven Ramaty High Energy Solar Spectroscopic Imager) and GOES (Geostationary Operational Environmental Satellites) events list from 2002 to 2015, and found out flare samples that have simple lightcurves at 25--50 keV together with other criteria. A total of 276 flare samples were finally selected. We have analysed the tau distribution of these flares, as well as the relationship between the loop length (represented by the distance between two footpoint sources d) and tau. We found that: (1) 227 sample flares present $\tau > 0$, which means that about 82% of total samples deviate from the classical Neupert effect; (2) there is a roughly linear correlation between tau and d, that is, the longer the loop is, the later the maximum time of SXR with respect to the end of HXR; (3) there seems to have a critical distance, within which the classic Neupert effect works. These results confirm the necessity of modifying Neupert effect and expound its physical significance.