Supernova Seismology: Gravitational Wave Signatures of Rapidly Rotating Core Collapse

TL;DR

This paper investigates gravitational wave signals from rapidly rotating core-collapse supernovae, analyzing oscillation modes of the proto-neutron star to understand how GW spectra reveal progenitor star properties.

Contribution

It introduces a linear perturbation theory approach to estimate GW spectra from rotating core collapse, linking oscillation modes to observable GW features and progenitor characteristics.

Findings

Fundamental quadrupolar mode frequency: 0.70-0.80 kHz.

GW energy largely trapped within the PNS, leaking over ~10 ms.

Rotation and PNS structure significantly influence the GW spectrum.

Abstract

Gravitational waves (GW) generated during a core-collapse supernova open a window into the heart of the explosion. At core bounce, progenitors with rapid core rotation rates exhibit a characteristic GW signal which can be used to constrain the properties of the core of the progenitor star. We investigate the dynamics of rapidly rotating core collapse, focusing on hydrodynamic waves generated by the core bounce and the GW spectrum they produce. The centrifugal distortion of the rapidly rotating proto-neutron star (PNS) leads to the generation of axisymmetric quadrupolar oscillations within the PNS and surrounding envelope. Using linear perturbation theory, we estimate the frequencies, amplitudes, damping times, and GW spectra of the oscillations. Our analysis provides a qualitative explanation for several features of the GW spectrum and shows reasonable agreement with nonlinear hydrodynamic simulations, although a few discrepancies due to non-linear/rotational effects are evident. The dominant early postbounce GW signal is produced by the fundamental quadrupolar oscillation mode of the PNS, at a frequency $0.70 \, {\rm kHz} \lesssim f \lesssim 0.80\,{\rm kHz}$, whose energy is largely trapped within the PNS and leaks out on a $\sim\!10$ ms timescale. Quasi-radial oscillations are not trapped within the PNS and quickly propagate outwards until they steepen into shocks. Both the PNS structure and Coriolis/centrifugal forces have a strong impact on the GW spectrum, and a detection of the GW signal can therefore be used to constrain progenitor properties.