A New Kilohertz Gravitational-Wave Feature from Rapidly Rotating Core-Collapse Supernovae

TL;DR

This study identifies two key gravitational-wave features from rotating core-collapse supernovae, linking them to specific instabilities and inner core dynamics, and suggests these signals can help determine the initial rotation rate of the collapsing star.

Contribution

The paper presents the first detailed analysis of kilohertz gravitational-wave features from rotating supernovae, connecting them to proto-neutron star deformation and instability mechanisms.

Findings

Identified two main GW features at ~300 Hz and ~1.3 kHz linked to m=1 deformation.

The 300 Hz feature appears in models with initial angular velocity 1.0-4.0 rad/s.

The 1.3 kHz feature originates from the high-density inner core of the PNS.

Abstract

We present self-consistent three-dimensional core-collapse supernova simulations of a rotating $20M_\odot$ progenitor model with various initial angular velocities from $0.0$ to $4.0$ rad s$^{-1}$ using a smoothed particle hydrodynamics code, SPHYNX, and a grid-based hydrodynamics code, FLASH. We identify two strong gravitational-wave features, with peak frequencies of $\sim300$ Hz and $\sim1.3$ kHz in the first $100$ ms postbounce. We demonstrate that these two features are associated with the $m=1$ deformation from the proto-neutron star (PNS) modulation induced by the low-$T/|W|$ instability, regardless of the simulation code. The $300$ Hz feature is present in models with an initial angular velocity between $1.0$ and $4.0$ rad s$^{-1}$, while the $1.3$ kHz feature is present only in a narrower range, from $1.5$ to $3.5$ rad s$^{-1}$. We show that the $1.3$ kHz signal originates from the high-density inner core of the PNS, and the $m=1$ deformation triggers a strong asymmetric distribution of electron anti-neutrinos. In addition to the $300$ Hz and $1.3$ kHz features, we also observe one weaker but noticeable gravitational-wave feature from higher-order modes in the range between $1.5$ and $3.5$ rad s$^{-1}$. Its peak frequency is around $800$ Hz initially and gradually increases to $900-1000$ Hz. Therefore, in addition to the gravitational bounce signal, the detection of the $300$ Hz, $1.3$ kHz, the higher-order mode, and even the related asymmetric emission of neutrinos, could provide additional diagnostics to estimate the initial angular velocity of a collapsing core.