Correlations between various hardness ratios of gamma-ray bursts

We study correlations between various hardness ratios of gamma-ray bursts ( GRBs) and investigate if there are any differences between the short- and l ong-duration classes of the objects in the distributions of the ratios. The results show that most of the hardness ratios are mutually correlated, but that the ratio defined at the lower energy bands is not correlated with th ose defined at the higher energy bands, the most significant correlations c ome from those ratios defined with both the lower and higher energy bands. It a also shown that the short-duration bursts tend to have higher values o f hardness ratios. We reach these conclusions that the slope of the higher part of the spectrum of most GRBs is independent of that of the lower part; emissions at higher energy bands from the bursts of both short- and long-d uration classes are significantly different for different sources, but radi ations at lower energy bands are similar; the spectra of the short-duration bursts is harder than that of the long-duration bursts. A possible interpr etation for these results involves Doppler boosting in the relativistic bea ming model. In addition, the study reveals that hardness ratios of the long -duration class are more mutually correlated than these of the short-durati on class; the data of hardness ratios for the long-duration class are much less scattered than those of the short-duration class. It is found that thi s difference is at least partially due to measurement errors.