Relativistic Outflows in Gamma-Ray Bursts

TL;DR

This paper reviews numerical simulations that explore how relativistic, collimated outflows in gamma-ray bursts can originate from different progenitor models, addressing the challenge of explaining jet formation.

Contribution

It synthesizes simulation results validating the collapsar and compact binary merger models for long and short GRBs, respectively.

Findings

Simulations support jet collimation in collapsar models for long GRBs.

Merger models can produce relativistic outflows consistent with observations.

Numerical results help understand the complex dynamics of GRB outflows.

Abstract

The possibility that gamma-ray bursts (GRBs) were not isotropic emissions was devised theoretically as a way to ameliorate the huge energetic budget implied by the standard fireball model for these powerful phenomena. However, the mechanism by which after the quasy-isotropic release of a few $10^{50} $erg yields a collimated ejection of plasma could not be satisfactory explained analytically. The reason being that the collimation of an outflow by its progenitor system depends on a very complex and non-linear dynamics. That has made necessary the use of numerical simulations in order to shed some light on the viability of some likely progenitors of GRBs. In this contribution I will review the most relevant features shown by these numerical simulations and how they have been used to validate the collapsar model (for long GRBs) and the model involving the merger of compact binaries (for short GRBs).