Modeling the GRB jet properties with 3D general relativistic simulations of magnetically arrested accretion flows

TL;DR

This paper uses 3D general relativistic magnetohydrodynamic simulations to explore how accretion disk properties influence the structure and evolution of gamma-ray burst jets, revealing structured, hollow jets with variable opening angles.

Contribution

It introduces a detailed simulation framework for modeling GRB jets based on different accretion disk initial conditions and magnetic field geometries, advancing understanding of jet formation and variability.

Findings

Jets are structured with hollow cores and higher Lorentz factors at angles > 9°.

Long GRB jets are narrower (~11°) compared to short GRB jets (~25°).

Jets exhibit time variability with estimated minimum timescales.

Abstract

We investigate the dependence of the GRB jet structure and its evolution on the properties of the accreting torus in the central engine. Our models numerically evolve the accretion disk around a Kerr black hole using 3D general relativistic magnetohydrodynamic simulations. We use two different analytical hydrodynamical models of the accretion disk, based on the Fishbone-Moncrief and Chakrabarti solutions, as our initial states for the structure of the collapsar disk and the remnant after a binary neutron star merger, respectively. We impose poloidal magnetic fields of two different geometries upon the initial stable solutions. We study the formation and evolution of the magnetically arrested disk state and its effect on the properties of the emitted jet. The jets produced in our models are structured and have a relatively hollow core and reach higher Lorentz factors at an angle $\gtrsim 9{^\circ}$ from the axis. The jet in our short GRB model has an opening angle of up to $\sim 25^{\circ}$ while our long GRB engine produces a narrower jet, of up to $\sim 11^{\circ}$. We also study the time variability of the jets and provide an estimate of the minimum variability timescale in our models. The application of our models to the GRB jets in the binary neutron star post-merger system and to the ultra-relativistic jets launched from collapsing stars are briefly discussed.