一类X射线发射度在脉冲相具有显著指数增长特征的太阳耀斑  

Solar Flares with an Exponential Growth of the Emission Measure in the Impulsive Phase Derived from X-ray Observations

作　　者：韩斐然[1,2,3] 刘四明[1,2] 

机构地区：[1]中国科学院紫金山天文台,南京210008 [2]中国科学院暗物质与空间天文重点实验室,南京210008 [3]中国科学院研究生院,北京100049

出　　处：《天文学报》2012年第6期482-499,共18页Acta Astronomica Sinica

基　　金：国家自然科学基金项目(11143007;11173063;11173064);973项目(2011CB811402)资助

摘　　要：太阳耀斑脉冲相的X射线光变曲线的复杂性表明此阶段有多种物理过程参与其中.基于某些显著的观测特征对耀斑分类可以用来探索这些特征的物理起源.对GOES(Geostationary Operational Environmental Satellite)卫星观测数据的分析表明有一类X射线发射度在脉冲相呈显著指数增长的耀斑.指数增长阶段的平均温度为正态分布.在此温度分布1σ之内的大多数耀斑属于B级或C级耀斑,其GOES低通道流量的峰值分布为对数正态分布.指数增长相的增长率和持续时间也遵循对数正态分布.持续时间分布范围大概为几十秒到几千秒.正如所预期的,增长时标同软X射线的衰减时标具有相关性.此外,指数增长相的增长率与持续时间呈强烈的反相关,而且随增长率的增大,对应的平均温度也有缓慢增大的趋势.The light curves of solar flares in the impulsive phase are complex in gen- eral, which is expected given the complexities of the flare environment in the magnetic field dominant corona. With the GOES （Geostationary Operational Environmental Satellite） observations, we however find that there are a subset of flares, whose impulsive phases are dominated by a period of exponential growth of the emission measure. The flares occurring from January 1999 to December 2002 are analyzed, and the results from the observations made with both GOES 8 and 10 satellites are compared to estimate the instrumental uncertainties. The frequency distribution of the mean temperature during this exponential growth phase has a normal distribution. Most flares within the la range of this temperature dis- tribution belong to the GOES class B or C with the frequency distribution of the peak flux of the GOES low-energy channel following a log-normal distribution. The frequency distri- bution of the growth rate, and the duration of the exponential growth phase also follow a log-normal distribution with the duration covering a range from half a minute to about half an hour. As expected, the growth time is correlated with the decay time of the soft X-ray flux. We also find that the growth rate of the emission measure is strongly anti-correlated with the duration of the exponential growth phase, and the mean temperature increases slightly with the increase of the growth rate. The implications of these results on the study of energy release in solar flares are discussed at the end.

关 键 词：粒子加速 等离子体 辐射机制:热 太阳:耀斑 太阳:X射线 

分 类 号：P182[天文地球—天文学]