TEST FOR COSMOLOGICAL TIME DILATION IN LONG GAMMA-RAY BURSTS

We present a test to investigate cosmological time dilation in long ga mma-ray bursts (t(90) > 1.5 s) using V, the ratio of expected peak cou nts in 64 and in 1024 ms. The theoretical evolution of V with redshift shows that dimmer bursts have flatter peaks than brighter ones when w e assume that (1) the bursters are at cosmological distances, (2) the bursts have standard exponential profiles, and (3) the burst peak dura tion follows a power law in narrowing with cosmological redshift energ y. The calculated V-distribution of long bursts versus intensity in a Friedmann universe with Omega = 1 and Lambda = 0 is consistent with th at found from previous results for long bursts. The estimated redshift is z similar to 2, and the time dilation factor with energy correctio n is similar to 1.8.