Exploring the central engines of gamma-ray bursts from prompt light curves

Hyperaccreting stellar-mass black hole systems are leading candidates for the central engines of gamma-ray bursts (GRBs). Their jets are thought to be powered by either the Blandford–Znajek (BZ) process or neutrino-dominated accretion flows (NDAFs), but discriminating between these mechanisms remains challenging. To address this, we proposed using the luminosity decay slope ( d ) of GRB light curves to distinguish between the BZ and NDAF mechanisms, thereby linking the light-curve morphology to the central engine physics. By analysing 85 single-peaked GRBs with fast-rise, exponential-decay (FRED) profiles observed by Swift/BAT using 64 ms background-subtracted light curves, we fitted the decay slope ( d ) with the empirical Kocevski–Ryde–Liang (KRL) function and compared the results with theoretical predictions for the BZ ( d ≈ 1.67) and the NDAF ( d ≈ 3.7–7.8) mechanisms. We find that the decay slope ( d ) can differentiate central engine mechanisms, with 15 GRBs consistent with the BZ mechanism and 22 supporting the NDAF mechanism. However, most events exhibit slopes within the range 2 < d < 4, suggesting a hybrid of mechanisms, with NDAF being dominant.