Chinese Acad Sci, Inst High Energy Phys, Lab Cosm Rays & High Energy Astrophys, Beijing, Peoples R China
Article; Proceedings Paper
We determine the characteristic variability time Scales for 410 bright long GRBs by locating the maximums of their Power Density Spectra (PDSs) defined and calculated in the time domain. The averaged characteristic variability time scale decreases with peak fluxe. This is consistent with the time dilation effect expected by cosmological origin of GRBs. The occurrence distribution of the characteristic variability time scale shows bimodality, which might be interpreted as that the long GRB sample is composed of two sub-classes with different intrinsic characteristic variability time scales.