中文摘要：

太阳耀斑中硬X射线（HXR）光子谱的低能变平过去一般认为是由于耀斑中非热电子的低能截止造成的，但现在也有作者认为耀斑光子与下层大气的逆康普顿散射（albedo效应）或者其他作用也能够使得HXR光子谱出现低能变平的情形．采用Gan et al．（2001，2002）中提出的求非热电子低能截止的方法，统计分析了Ramaty High Energy Solar Spectroscopy Imager（RHESSI）卫星在2002-2005年间观测的100个耀斑，发现经albedo校正，有18个耀斑的HXR光子谱可以利用单幂律谱来拟合，在80个可以用双幂律谱来拟合HXR光子谱的耀斑中，有21个耀斑可以直接用单幂律电子谱加一个低能截止来解释．低能截止范围为20—50keV，平均值约为30keV．同时也分析了耀斑光子谱特征的其他可能解释．

英文摘要：

The flattening of the power-low HXR spectrum towards the lower energies was generally due to the existence of lower energy cutoff of the power-law electrons. Some other explanations, like albedo effects, were proposed recently on this phenomenon. With the method of Gan et ai.（2001,2002）, we studied 100 flare samples observed by RHESSI. We found that among 100 albedo-corrected spectra of the flare samples, there are 21 on which we can use a power-law electron beam with a sharp low energy cutoff to explain. The derived low energy cutoff ranges from 20 to 50keV and averages about 30keV.