The emission time of gamma-ray bursts

The concept of emission time tau(N) is suggested as a temporal parameter wh ich is complementary to the classical parameters of duration times T-50 and T-90. The emission time is defined as the time of emission of N% of the to tal fluence. The definition adds the time bins of high fluence in decreasin g fluence rank until N% of the fluence has been reached. The emission time interval excludes low-emission intervals of bursts, and so the emission tim e characterizes the state of high-power emission. The distribution of this new parameter is found to be bimodal for bright bursts. The distributions o f emission time tau(30) and tau(50), for groups based on burst intensity, a re also compared.