A Clarification on the invariable point in the power-law energy spectra of non-thermal electrons of solar flares

The invariable point of non-thermal electrons was proposed two years ago, based on analyzing the two intense gamma-ray line flares observed with the X2 detector on GRS/SMM. Due to too strong hard X-ray flux in those two flares, the influence of pile-up effect might not be fully excluded. In this paper, we check the invariable point by using some medium hard X-ray events observed with HXRBS/SMM and BATSE/CGRO. It is found that the invariable point could indeed appear in some weaker hard X-ray events, in which the pile-up effect cannot play a role. Further refinement should be based on the observations with a high energy resolution. This revised version was published online in July 2006 with corrections to the Cover Date.