THE DISTANCE SCALE OF COSMOLOGICAL GAMMA-RAY BURSTS

The isotropic but radially non-uniform distribution of gamma-ray burst s (GRBs) observed with the Burst and Transient Source Experiment (BATS E) on board the Compton Gamma Ray Observatory (CGRO) suggests that the bursts may be at cosmological distances. At such distances, the expan sion of the Universe should have two main effects on the statistics of gamma-ray bursts: first, it should stretch the temporal structure, re sulting in dimmer bursts to be longer than bright bursts; second, it w ould decrease the number of gamma-ray bursts with distance, resulting in the value of [ V/V-max ] to be smaller than 0.5. Here we have used the observed time dilation (similar to 2) to estimate the distance of gamma-ray bursts, and then we use another method, calculating the valu e of [ V/V-max ] to obtain the distance of gamma-ray bursts. These two methods are independent and should be self-consistent. Our results sh ow that the redshift of the dimmest bursts determined from these two d istinct methods are consistent, z(dimmest) similar to 3.2, correspondi ng to a burst luminosity of L similar to 4 x 10(50)ergs(-1), which is different from the results reported previously.