Gravitational Wave Signatures of Hyperaccreting Collapsar Disks

TL;DR

This study uses relativistic magnetohydrodynamic simulations to predict gravitational wave signatures from hyperaccreting collapsar disks, highlighting neutrino emission as a dominant GW source detectable by future space interferometers.

Contribution

The paper introduces detailed simulations of collapsar disks including microphysics and neutrino effects, providing new predictions for gravitational wave signals from long gamma-ray burst progenitors.

Findings

Neutrino GWs increase monotonically over time.

Neutrino GWs are larger than matter motion GWs.

Detection possible within 100 Mpc with future interferometers.

Abstract

By performing two-dimensional special relativistic (SR) magnetohydrodynamic simulations, we study possible signatures of gravitational waves (GWs) in the context of the collapsar model for long-duration gamma-ray bursts. In our SR simulations, the central black hole is treated as an absorbing boundary. By doing so, we focus on the GWs generated by asphericities in neutrino emission and matter motions in the vicinity of the hyperaccreting disks. We compute nine models by adding initial angular momenta and magnetic fields parametrically to a precollapse core of a $35 M_{\odot}$ progenitor star. As for the microphysics, a realistic equation of state is employed and the neutrino cooling is taken into account via a multiflavor neutrino leakage scheme. To accurately estimate GWs produced by anisotropic neutrino emission, we perform a ray-tracing analysis in general relativity by a post-processing procedure. By employing a stress formula that includes contributions both from magnetic fields and special relativistic corrections, we study also the effects of magnetic fields on the gravitational waveforms. We find that the GW amplitudes from anisotropic neutrino emission show a monotonic increase with time, whose amplitudes are much larger than those from matter motions of the accreting material. We show that the increasing trend of the neutrino GWs stems from the excess of neutrino emission in the direction near parallel to the spin axis illuminated from the hyperaccreting disks. We point out that a recently proposed future space-based interferometer like Fabry-Perot type DECIGO would permit the detection of these GW signals within $\approx$ 100 Mpc.