Evidence of Self-organized Criticality in the Prompt Emission of a Bright Gamma-Ray Burst

Gamma-ray bursts (GRBs) are the most energetic explosive events in the Universe, yet the physical mechanism of their prompt emission remains a mystery. In particular, it is unclear whether the energy dissipation mechanism in the GRB jet is dominated by kinetic energy or magnetic energy. Here we studied the pulses in the prompt emission of the second brightest GRB to date, GRB 230307A, which was accurately measured by the Gravitational Wave High-energy Electromagnetic Counterpart All-sky Monitor (GECAM), with a focus on the cumulative distributions of peak counts and duration of pulses as well as on the waiting time between pulses. We find that these cumulative distributions show scale-invariant behavior, well consistent with the prediction of the self-organized criticality (SOC) theory. This is the first robust evidence of a SOC feature in the prompt emission of a single GRB. Moreover, the statistical properties of pulses in the prompt emission of GRB 230307A are very similar to those of solar flares. Our findings suggest that the prompt emission of GRBs is powered by the dissipation of magnetic energy in the ultrarelativistic jet, supporting the Poynting-flux-dominated prompt models.