3D magnetised jet break-out from neutron-star binary merger ejecta: afterglow emission from the jet and the ejecta

TL;DR

This study uses 3D relativistic magnetohydrodynamic simulations to model jet break-out from neutron-star merger ejecta, analyzing the resulting afterglow emission and comparing it with observations from GRB170817A.

Contribution

It provides the first 3D simulation confirmation of jet structure features and models the afterglow emission to match observational data, including kilonova and superluminal motion.

Findings

Relativistic outflow has a hollow core of about 4 degrees.

Jet opening angle is greater than 10 degrees.

Simulated afterglow fits GRB170817A observations and constrains observer angle.

Abstract

We perform three-dimensional (3D) general-relativistic magnetohydrodynamic simulations to model the jet break-out from the ejecta expected to be produced in a binary neutron-star merger. The structure of the relativistic outflow from the 3D simulation confirms our previous results from 2D simulations, namely, that a relativistic magnetized outflow breaking out from the merger ejecta exhibits a hollow core of $\theta_{\rm core}\approx4^{\circ}$, an opening angle of $\theta_{\rm jet}\gtrsim10^{\circ}$, and is accompanied by a wind of ejected matter that will contribute to the kilonova emission. We also compute the non-thermal afterglow emission of the relativistic outflow and fit it to the panchromatic afterglow from GRB170817A, together with the superluminal motion reported from VLBI observations. In this way, we deduce an observer angle of $\theta_{\rm obs}= 35.7^{\circ \,\,+1.8}_{\phantom{\circ \,\,}-2.2}$. We further compute the afterglow emission from the ejected matter and constrain the parameter space for a scenario in which the matter responsible for the thermal kilonova emission will also lead to a non-thermal emission yet to be observed.