Resonant amplification of multimessenger emission in rotating stellar core collapse

Abstract

In a series of axisymmetric core-collapse supernova simulations extending up to $\sim 2\,\mathrm{s}$, we identify a regime of pre-collapse central rotation rates ($\sim 1\,\mathrm{Hz}$) that greatly enhances the emission of gravitational waves (GWs) during extended periods of time after bounce. The enhancement is a consequence of the resonance between the frequency of the fundamental quadrupolar $^2f$-mode of oscillation of the proto-neutron star and the frequency of the epicyclic oscillations at the boundary of the inner core. We observe periods of about several hundred milliseconds each where the resonance is active. The GW emission enhancement produces a correlated resonant modulation of the associated neutrino signal at the same frequencies. With GW frequencies of $\mathcal{O}(1\,\mathrm{kHz})$ and strain amplitudes within the sensitivity curves of current and next-generation interferometers at distances of $\mathcal{O}(1\,\mathrm{Mpc})$, this resonant-amplification mechanism may represent a potential game-changer for unveiling the supernova explosion mechanism through multimessenger astronomy.

Figures (7)

• Figure 1: Top panel: strains emitted by a source at distance $\mathcal{D}$ for models SR (red), IR (black), and FR (yellow). Bottom panel: Spectrogram of the signal for model IR. Blue lines represent the fundamental frequency (solid), the first (dashed) and the second (dotted) overtones of the epicyclic frequency, with shaded regions showing the associated uncertainties. The green line indicates the fundamental quadrupolar mode, computed using the quasi-universal relation from TorresForne19.
• Figure 2: Snapshots of the radial velocity illustrating a full oscillation cycle of the at (clockwise from the top-left panel) $\unit[1.1283]{s}$, $\unit[1.1285]{s}$, $\unit[1.1287]{s}$, and $\unit[1.1291]{s}$. Each of the panels shows one hemisphere only. Black lines represent the radius, defined as the isodensity line at $\unit[10^{11}]{g/cm^3}$. Streamlines represent the velocity field. Background colours indicate inward (blue) and outward-moving (red) matter.
• Figure 3: Normalized Fourier transform of the equatorial density ($l=0$), $v_\theta$ at $\pi/4$ ($l=2$), both outside of taken the core outer boundary at $\unit[25]{km}$, and of the signal ($\tilde{h}_+$) for the time interval $\unit[1.1-1.4]{s}$. The solid, dashed, and dotted black vertical lines represent the fundamental frequency and the first and second overtones of the average epicyclic frequency, respectively. Shaded regions indicate the uncertainty associated with the frequencies. The dash-dotted line represents the average $^2f$-mode frequency derived with the relations in TorresForne19.
• Figure 4: Characteristic spectra for models SR (red), IR (black), and FR (yellow), assuming a source distance of $\unit[1]{Mpc}$, compared with the design sensitivity curves of current and next-generation interferometers. $h_\texttt{char}$ has been convolved over a window of $\unit[10]{Hz}$ for better visualization.
• Figure 5: Top panel: evolution of the matching score between the spectrograms of the $\overline{\nu}_\textnormal{e}$ and signals. Middle panel: neutrino luminosities of electron antineutrinos (black line), electron neutrinos (dark gray, shifted by $\unit[0.2\times10^{53}]{erg/s}$), heavy lepton neutrinos (light gray, shifted by $\unit[0.4\times10^{53}]{erg/s}$). Bottom panel: spectrogram of the antineutrino luminosities, with the shaded regions and blue lines denoting the same quantities as in Figure \ref{['fig:GW_spectro']}. Both panels refer to model IR.