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

¹ School of Physics and Physical Engineering, Qufu Normal University, Qufu 273165, China
² Department of Physics, Huazhong University of Science and Technology, Wuhan 430074, China
³ Department of Astronomy, Xiamen University, Xiamen, Fujian 361005, China
⁴ Department of Physics, Anhui Normal University, Wuhu, 241002 Anhui, China
⁵ Department of Physics, Nanchang University, Nanchang 330031, PR China
⁶ School of Astronomy and Space Science, Nanjing University, Nanjing 210023, China

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Received: 13 August 2025
Accepted: 2 February 2026

Abstract

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.