A large-scale magnetic field produced by a solar-like dynamo in binary neutron star mergers

TL;DR

This paper demonstrates through high-resolution simulations that an alpha-omega dynamo driven by magnetorotational instability can generate the large-scale magnetic fields necessary for short gamma-ray bursts in binary neutron star mergers, supporting the magnetar scenario.

Contribution

It provides the first ab initio simulation showing the dynamo process building large-scale magnetic fields in neutron star merger remnants within full general relativity.

Findings

Magnetic fields reach strengths capable of powering relativistic jets.

The remnant produces Poynting-flux dominated outflows with luminosity ~10^{51} erg/s.

Mass ejection of about 0.1 solar masses driven by magnetic processes.

Abstract

The merger of neutron stars drives a relativistic jet which can be observed as a short gamma-ray burst. A strong large-scale magnetic field is necessary to launch the relativistic jet. However, the magnetohydrodynamical mechanism to build up this magnetic field remains uncertain. Here we show that the $\alpha\Omega$ dynamo mechanism driven by the magnetorotational instability builds up the large-scale magnetic field inside the long-lived binary neutron star merger remnant by performing an {\it ab initio} super-high resolution neutrino-radiation magnetohydrodynamics merger simulation in full general relativity. As a result, the magnetic field induces the Poynting-flux dominated relativistic outflow with the luminosity $\sim 10^{51}$\,erg/s and magnetically-driven post-merger mass ejection with the mass $\sim 0.1M_\odot$. Therefore, the magnetar scenario in binary neutron star mergers is possible. These can be the engines of short-hard gamma-ray bursts and very bright kilonovae. Therefore, this scenario is testable in future observation.