Striped Jets in Post Neutron Star Merger Systems

TL;DR

This paper uses 3D relativistic magnetohydrodynamic simulations to demonstrate the formation of magnetically striped jets in post-neutron star merger systems, revealing their potential role in gamma-ray burst variability.

Contribution

It presents the first first-principles simulations showing striped jet formation with detailed analysis of their properties and implications for gamma-ray burst observations.

Findings

Magnetically striped jets form in all simulations.

Stripes result from magnetic flux reversals in the accretion disk.

Power and variability of stripes match short gamma-ray burst observations.

Abstract

Models invoking magnetic reconnection as the particle acceleration mechanism within relativistic jets often adopt a gradual energy dissipation profile within the jet. However, such a profile has yet to be reproduced in first-principles simulations. Here, we perform a suite of 3D general relativistic magnetohydrodynamic simulations of post-neutron star merger disks with an initially purely toroidal magnetic field. We explore the variations in both the microphysics (e.g., nuclear recombination, neutrino emission) and system parameters (e.g., disk mass). In all our simulations, we find the formation of magnetically striped jets. The stripes result from the reversals in the poloidal magnetic flux polarity generated in the accretion disk. The simulations display large variations in the distributions of stripe duration, $\tau$, and power, $\langle P_{\Phi} \rangle$. We find that more massive disks produce more powerful stripes, the most powerful of which reaches $\langle P_{\Phi} \rangle \sim 10^{49}$~erg~s$^{-1}$ at $\tau \sim 20$~ms. The power and variability that result from the magnetic reconnection of the stripes agree with those inferred in short duration gamma-ray bursts. We find that the dissipation profile of the cumulative energy is roughly a power-law in both radial distance, $z$, and $\tau$, with the slope in the range, $\sim 1.7-3$; more massive disks display larger slopes.