SIMBAD references

It was found by Amati et al. in 2002 that for a small sample of nine gamma-ray bursts (GRBs), more distant events appear to be systematically harder in the soft gamma-ray band. Here, we have collected a larger sample of 65 GRBs, whose time-integrated spectra are well established and can be well fitted with the so-called Band function. It is confirmed that a correlation between the redshifts (z) and the low-energy indices (α) of the Band function does exist, though it is a bit more scattered than the result of Amati et al. This correlation cannot be simply attributed to the effect of photon reddening. Furthermore, correlations between α and E_peak (the peak energy in the νF_ν spectrum in the rest frame), α and E_iso(the isotropic energy release), and α and L_iso(the isotropic luminosity) are also found, which indicate that these parameters are somehow connected. The results may provide useful constraints on the physics of GRBs.