Microphysics in the gamma ray burst central engine

TL;DR

This paper models the microphysics of a gamma ray burst central engine, focusing on the accretion torus, nuclear reactions, neutrino flux, and nucleosynthesis, to better understand the engine's structure and observable signatures.

Contribution

It introduces a self-consistent relativistic MHD model with an advanced nuclear equation of state for GRB engines, including nucleosynthesis and energy transfer mechanisms.

Findings

Detailed structure of the accretion torus and winds

Neutrino flux estimates from nuclear reactions

Potential signatures of radioactive decay in GRB signals

Abstract

We calculate the structure and evolution of a gamma ray burst central engine where an accreting torus has formed around the newly born black hole. We study the general relativistic,MHD models and we self-consistently incorporate the nuclear equation of state. The latter accounts for the degeneracy of relativistic electrons, protons, and neutrons, and is used in the dynamical simulation, instead of a standard polytropic -law. The EOS provides the conditions for the nuclear pressure in the function of density and temperature, which evolve with time according to the conservative MHD scheme. We analyze the structure of the torus and outflowing winds, and compute the neutrino flux emitted through the nuclear reactions balance in the dense and hot matter. We also estimate the rate of transfer of the black hole rotational energy to the bipolar jets. Finally, we elaborate on the nucleosynthesis of heavy elements in the accretion flow and the wind, through computations of the thermonuclear reaction network. We discuss the possible signatures of the radioactive elements decay in the accretion flow. We suggest that further detailed modeling of the accretion flow in GRB engine, together with its microphysics, may be a valuable tool to constrain the black hole mass and spin. It can be complementary to the gravitational wave analysis, if the waves are detected with an electromagnetic counterpart.