Investigating the Temporal Evolution of Gamma-Ray Burst Central Engine Parameters Based on Numerical Simulations

A hyperaccreting stellar-mass black hole (BH) has been proposed as the candidate central engine of gamma-ray bursts (GRBs). Comparing the predictions from the central engine models with the temporal behavior of GRBs is of great interest. In this paper, using the open-source GRMHD HARM-COOL code, we evolve several 2D magnetized hyperaccreting BH models with realistic equation of state in a fixed curved space-time background. We extend the code to include the calculation of neutrino annihilation power. We then study the time evolution of BH central engine parameters, i.e., the neutrino annihilation power, the Blandford-Znajke (BZ) power, and the initial magnetization $\sigma_0$. We find that the neutrino power is generally consistent with previous analytical results. Usually, the neutrino annihilation process tends to launch a thermal ``fireball'', while the BZ jet is Poynting-flux-dominated. Our results, especially the evolution characteristics of $\sigma_0$ may help to understand the complex GRB spectral behavior.