Gravitational-Wave Signals for Supernova Explosions of Three-Dimensional Progenitors

TL;DR

This study analyzes gravitational-wave signals from two state-of-the-art 3D core-collapse supernova models (s12.28 and s18.88) evolved from 3D progenitors through several seconds after core bounce using Prometheus-Vertex. It separately evaluates GW emission from hydrodynamical mass motions and from anisotropic neutrino emission, in both time and frequency domains, and compares results with recent literature while assessing detectability by current and next-generation detectors. The main findings are that the GW signals exhibit familiar features from neutrino-driven explosions (prompt convection, SASI, PNS oscillations, and ejecta memory) with no clear diagnostic tied to pre-collapse 3D oxygen-shell activity, and that matter GW signals dominate over neutrino GW signals in energy; nevertheless, neutrino memory contributes notably at low frequencies. The results indicate promising detectability for a Galactic SN in the 1–2000 Hz band with existing and planned interferometers, and they motivate a broader set of 3D-progenitor simulations to determine the general impact of pre-collapse perturbations on GW signatures.

Abstract

Core-collapse supernovae (SNe) are sources of gravitational waves (GWs) produced by hydrodynamical instabilities and highly time-dependent anisotropies of the neutrino radiation. In this work we analyze both contributions to the GW signal for two state-of-the-art three-dimensional (3D) SN models computed with the Prometheus-Vertex neutrino-hydrodynamics code. In contrast to the far majority of models analyzed for GWs so far, our core-collapse simulations were started with 12.28 M_sun (18.88 M_sun) progenitors, whose final hour (7 min) of convective oxygen-shell burning was computed in 3D and featured a vigorous oxygen-neon shell merger. The corresponding large-scale asymmetries in the oxygen layer are conducive to buoyancy-aided neutrino-driven explosions. The models were continuously evolved in 3D from the pre-collapse evolution until 5.11 s (1.68 s) after the core bounce. The GW signals result from the well-known dynamical phenomena in the SN core such as prompt postshock convection, neutrino-driven convection, the standing accretion shock instability, proto-neutron star oscillations, and anisotropic ejecta expansion. They do not exhibit any new or specific features that can be unambiguously connected to the powerful pre-collapse activity in the progenitors, but we identify interesting differences compared to results in the literature. We also discuss measurement prospects by interferometers, confirming that GW signals from future Galactic SNe will be detectable with existing and next-generation experiments working in the frequency range f ~ 1-2000 Hz.

Figures (23)

• Figure 1: Evolution of the shock radius versus post-bounce time $t_\mathrm{pb}$ during the first 600 ms after bounce (left) and until the end of our simulations (right) for models s12.28 (red) and s18.88 (blue). The solid lines show the spherically averaged shock radius, the shaded bands indicate the range between the minimum and maximum shock radii. Note the different scales on the axes of both plots.
• Figure 2: Snapshots of model s12.28, showing cross-sectional cuts ($x$-$y$ plane) of the specific entropy in the postshock region (top row), the radial gas velocity in the surroundings of the PNS (second row), and the radial flow velocity (third row) and kinetic energy density in and near the PNS (bottom row), all color-coded according to the color bars on the right side of each row. The dashed lines, with growing radius, correspond to contours for spherically averaged matter densities of $3\times10^{12}$, $1\times10^{11}$, and $5\times10^{9}$ g cm$^{-3}$. Note the different and time-dependent length scales indicated by yard sticks. The post-bounce times of the snapshots in each column are given in the top panels. In the upper two rows one can recognize outward-rising high-entropy plumes of neutrino-heated matter separated by lower-entropy accretion downflows. In the lower two rows one can witness a shell with growing radial depth where convection takes place in the PNS interior, surrounded by a gravity-wave perturbed, convectively stable accretion layer. Intense yellow and orange in this layer in the bottom panels indicate rapid rotation due to angular momentum received from accretion downflows.
• Figure 3: Snapshots of model s18.88, showing cross-sectional cuts ($x$-$y$ plane) of the specific entropy in the postshock region (top row), the radial gas velocity in the surroundings of the PNS (second row), and the radial flow velocity (third row) and kinetic energy density in and near the PNS (bottom row), all color-coded according to the color bars on the right side of each row. The dashed lines, with growing radius, correspond to contours for spherically averaged matter densities of $3\times10^{12}$, $1\times10^{11}$, and $5\times10^{9}$ g cm$^{-3}$. Note the different and time-dependent length scales indicated by yard sticks. The post-bounce times of the snapshots in each column are given in the top panels. In the upper two rows one can recognize outward-rising high-entropy plumes of neutrino-heated matter separated by lower-entropy accretion downflows. In the lower two rows one can witness a shell with growing radial depth where convection takes place in the PNS interior, surrounded by a gravity-wave perturbed, convectively stable accretion layer. Intense yellow and orange in this layer in the bottom panels indicate rapid rotation due to angular momentum received from accretion downflows.
• Figure 4: Snapshots of accretion and PNS dynamics in model s12.28 between 1.6 s and 3.2 s after bounce. The panels show cross-sectional cuts in the $x$-$y$ and $x$-$z$ planes (labeled on the left of each row) for the specific entropy (top two rows), the radial gas velocity in the vicinity of the PNS (middle two rows), and the kinetic energy density in and near the PNS (bottom two rows). The color coding is defined by the color bars on the right. The outer (inner) dashed circle marks the contour for a spherically averaged matter density of $10^{11}$ g cm$^{-3}$ ($10^{13}$ g cm$^{-3}$). Note the different and time-dependent length scales indicated by the yard sticks. The post-bounce times of the snapshots in each column are given in the top panels. In the upper four rows one can recognize outward-rising high-entropy plumes of neutrino-heated matter separated by lower-entropy accretion downflows. In the bottom two rows one can witness a shell with growing radial depth where convection takes place in the PNS interior, surrounded by a gravity-wave perturbed, convectively stable accretion layer. Intense yellow and orange in this layer in the bottom panels indicate rapid rotation due to angular momentum received from accretion downflows.
• Figure 5: Mass-inflow rate (upper panels) and PNS kinetic energy (lower panels) as functions of post-bounce time $t_\mathrm{pb}$ in models s12.28 (left) and s18.88 (right). The mass-inflow rate is evaluated in accretion downflows (i.e., flows with negative radial velocity $v_r<0$) at a radius of $R = 400$ km (light gray), at twice the time-dependent PNS radius $R_\mathrm{ns}$ (dark gray), and at 1.1 times the PNS radius (black), where the PNS radius is defined at a spherically averaged density of $10^{11}$ g cm$^{-3}$. The kinetic energy inside the PNS is measured in volumes bounded by the PNS radius (black) and outer radii corresponding to spherically averaged densities of $3 \times 10^{12}$ g cm$^{-3}$ (dark blue) and $10^{13}$ g cm$^{-3}$ (light blue), respectively. The lowest density roughly corresponds to the PNS surface, the last two densities are near the outer edge of the PNS convection layer (see Figs. \ref{['fig:Dynamics_s12.28']}--\ref{['fig:LateDynamics_s12.28']}).