  Precursors provide important clues to the nature of gamma-ray burst (GRB)
central engines and can be used to contain GRB physical processes. In this
letter, we study the self-organized criticality in precursors of long GRBs in
the third Swift/BAT Catalog. We investigate the differential and cumulative
size distributions of 100 precursors, including peak flux, duration, rise time,
decay time, and quiescent time with the Markov Chain Monte Carlo technique. It
is found that all of the distributions can be well described by power-law
models and understood within the physical framework of a self-organized
criticality system. In addition, we inspect the cumulative distribution
functions of the size differences with a q-Gaussian function. The
scale-invariance structures of precursors further strengthen our findings.
Particularly, similar analyses are made in 127 main bursts. The results show
that both precursors and main bursts can be attributed to an self-organized
criticality system with the spatial dimension S = 3 and driven by the similar
magnetically dominated process.
