Circular polarization of gravitational waves from non-rotating supernova cores: a new probe into the pre-explosion hydrodynamics

TL;DR

This paper demonstrates that the circular polarization of gravitational waves from non-rotating supernova cores can reveal details about pre-explosion hydrodynamics, especially SASI activity, with potential for improved detection over amplitude-based methods.

Contribution

It introduces the use of GW circular polarization analysis from 3D-GR simulations as a new probe into supernova pre-explosion dynamics, highlighting its detection advantages.

Findings

GW polarization amplitude increases with SASI activity.

Characteristic low-frequency modulation (100-200 Hz) linked to SASI.

Detection horizon for polarization exceeds that of GW amplitude.

Abstract

We present an analysis of the circular polarization of gravitational-waves (GWs) using results from three-dimensional (3D), general relativistic (GR) core-collapse simulations of a non-rotating $15 M_{\odot}$ star. For the signal detection, we perform a coherent network analysis taking into account the four interferometers of LIGO Hanford, LIGO Livingston, VIRGO, and KAGRA. We focus on the Stokes $V$ parameter, which directly characterizes the asymmetry of the GW circular polarization. We find that the amplitude of the GW polarization becomes bigger for our 3D-GR model that exhibits strong activity of the standing accretion shock instability (SASI). Our results suggest that the SASI-induced accretion flows to the proto-neutron star (PNS) lead to a characteristic, low-frequency modulation (100 $\sim$ 200 Hz) in both the waveform and the GW circular polarization. During the vigorous SASI phase, we observe that the GW polarization switches from the right- to left-handed mode, which is clearly visible in the spectrogram. By estimating the signal-to-noise ratio of the GW polarization, we demonstrate that the detection horizon of the circular polarization extends by more than a factor of several times farther comparing to that of the GW amplitude. Our results suggest that the GW circular polarization, if detected, could provide a new probe into the pre-explosion hydrodynamics such as the SASI activity and the $g$-mode oscillation of the PNS.