Bimodal distribution of the autocorrelation function in gamma-ray bursts

Autocorrelation functions (ACFs) are studied for a sample of 16 long gamma-ray bursts (GRBs) with known redshift z, that were observed by the BATSE and Konus experiments. When corrected for cosmic time dilation, the ACF shows a bimodal distribution. A narrow width class (11 bursts) has at half-maximum a mean width s with a relative dispersion of ∼32%, while a broad width class (5 bursts) has s with a ∼4% dispersion. The separation between the two mean values is highly significant (). This temporal property could be used on the large existing database of GRBs with unknown redshift. The broad width set shows a very good linear correlation between width at half-maximum and , with a correlation coefficient and a probability of chance alignment <0.0004. The potential application of this correlation to cosmology studies is discussed, using it in combination with recently proposed luminosity indicators.