STATISTICS OF GAMMA-RAY BURST TEMPORAL ASYMMETRY

We study the temporal asymmetry of over 600 bursts from the BATSE 3B c atalog, encompassing a 200-fold range in peak flux. By comparing the r ates of rise and fall of the flux near the highest peak of each burst, we find that about two-thirds of the bursts exhibit a preferred asymm etry in the sense that the flux rises more rapidly than it falls, conf irming the conclusions of previous studies employing smaller databases . The probability that the observed time asymmetry is a statistical fl uctuation is less than 10(-5); therefore, models that predict time sym metry of the burst profile are ruled out. We find no statistically sig nificant correlation between burst temporal asymmetry and peak flux. T his result is consistent with both cosmological and local interpretati ons of the gamma-ray burst phenomenon.