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A negative correlation was found to exist between the low-energy spectralindex and the redshift of gamma-ray bursts (GRBs) by Amati(2002). It was laterconfirmed by Geng(2013) and Gruber(2014), but the correlation was also found tobe quite dispersive when the sample size was significantly expanded. In thisstudy, we have established two even larger samples of gamma-ray bursts tofurther examine the correlation. One of our sample is consisted of 316 GRBsdetected by the Swift satellite, and the other one is consisted of 80 GRBsdetected by the Fermi satellite. It is found that there is no correlationbetween the two parameters for the Swift sample, but there does exist a weaknegative correlation for the Fermi sample. The correlation becomes even moresignificant when the spectral index at the peak flux is considered. It isargued that the absence of the correlation in the Swift sample may be due tothe fact that Swift has a very narrow energy response so that it could notmeasure the low-energy spectral index accurately enough. Further studies basedon even larger GRB samples are solicited.

Redshift Dependence of the Low-energy Spectral Index of Gamma-Ray Bursts Revisited