Self-organized criticality in multi-pulse gamma-ray bursts.

The variability in multi-pulse gamma-ray bursts (GRBs) may help to reveal the mechanism of underlying processes from the central engine. To investigate whether the self-organized criticality (SOC) phenomena exist in the prompt phase of GRBs, we statistically study the properties of GRBs with more than 3 pulses in each burst by fitting the distributions of several observed physical variables with a Markov Chain Monte Carlo approach, including the isotropic energy E_iso, the duration time T, and the peak count rate P of each pulse. Our sample consists of 454 pulses in 93 GRBs observed by the CGRO/BATSE satellite. The best-fitting values and uncertainties for these power-law indices of the differential frequency distributions are: α E d = 1.54 ± 0.09 , α T d = 1.82 ± 0.15 + 0.14 a n d α P d = 2.09 − 019 + 0.18 , while the power-law indices in the cumulative frequency distributions are: α E c = 1.44 −s 0.10 + 0.08 , α T c = 1.75 − 0.13 + 0.141 a n d α P c = 1.99 − 019 + 0.16 . We find that these distributions are roughly consistent with the physical framework of a Fractal-Diffusive, Self-Organized Criticality (FD-SOC) system with the spatial dimension S = 3 and the classical diffusion β=1. Our results support that the jet responsible for the GRBs should be magnetically dominated and magnetic instabilities (e.g., kink model, or tearing-model instability) lead the GRB emission region into the SOC state. [ABSTRACT FROM AUTHOR]