Long duration gamma-ray bursts: hydrodynamic instabilities in collapsar disks

TL;DR

This paper uses 3D simulations to study how hydrodynamic instabilities in collapsar disks can facilitate the high accretion rates needed for long gamma-ray burst jets.

Contribution

It demonstrates the role of spiral hydrodynamic modes in angular momentum transfer and accretion in collapsar disks, using advanced 3D SPH simulations with microphysics.

Findings

Spiral structures form rapidly in the accretion disk.

Hydrodynamic instabilities enhance angular momentum transfer.

High accretion rates necessary for gamma-ray burst jets are achieved.

Abstract

We present 3D numerical simulations of the early evolution of long-duration gamma-ray bursts in the collapsar scenario. Starting from the core-collapse of a realistic progenitor model, we follow the formation and evolution of a central black hole and centrifugally balanced disk. The dense, hot accretion disk produces freely-escaping neutrinos and is hydrodynamically unstable to clumping and to forming non-axisymmetric (m=1, 2) modes. We show that these spiral structures, which form on dynamical timescales, can efficiently transfer angular momentum outward and can drive the high required accretion rates (>=0.1-1 M_sun) for producing a jet. We utilise the smoothed particle hydrodynamics code, Gadget-2, modified to implement relevant microphysics, such as cooling by neutrinos, a plausible treatment approximating the central object and relativistic effects. Finally, we discuss implications of this scenario as a source of energy to produce relativistically beamed gamma-ray jets.