Log-Normal Waiting Time Widths Characterize Dynamics

Many astronomical phenomena, including Fast Radio Bursts and Soft Gamma Repeaters, consist of brief, separated, seemingly aperiodic events. The intervals between these events vary randomly, but there are epochs of greater activity, with shorter mean intervals, and of lesser activity, with longer mean intervals. This variability can be quantified by a single dimensionless parameter, the width of a log-normal fit to the distribution of waiting times between events. If the distribution of event strengths is a power law, as is often the case, this parameter is independent of the detection threshold and is a robust measure of the intrinsic variability of the waiting times and of the underlying dynamics.