Supernova seismology: gravitational wave signatures of rapidly rotating core collapse

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 kHz f 0.80 kHz, whose energy is largely trapped within the PNS and leaks out on a ∼ 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.

Equation of state effects on gravitational waves from rotating core collapse

“…quadrupole) fundamental mode (i.e. no radial nodes) [55,112]. The quadrupole oscillations can be seen in the postbounce velocity field that we plot in the left panel of After the PNS has rung down, other fluid dynamics, notably prompt convection, begin to dominate the GW signal, generating a stochastic GW strain whose timedomain evolution is sensitive to the perturbations from which prompt convection grows (e.g., [46,47,57,113]).…”

“…They last for a few cycles after bounce, are damped hydrodynamically [112], and cause the postbounce oscillations in the GW signal that are apparent in the left panel of Fig. 4.…”

“…4) and from GWs up to t be þ 6 ms (empirically chosen to produce reliable PNS oscillation frequencies). We begin with a simulation with intermediate rotation and subtract the former bounce spectrum from the latter full spectrum and we take the largest spectral feature in the window of 600 to 1075 Hz to be the l ¼ 2 f-mode peak frequency f peak [55,112]. The spectral windows for simulations with the same value of A and adjacent values of Ω 0 are centered at this frequency and have a width of 75 Hz.…”

Probing mass-radius relation of protoneutron stars from gravitational-wave asteroseismology

“…Unlike a cold NS, the perturbative analyses in the case of a PNS are only a few [37][38][39][40]. This may come from the difficulty for providing the background model for the PNS.…”

Protoneutron Star Properties via Gravitational Wave Asteroseismology

“…The possibilities for obtaining the interior information of source objects with the asteroseismology have been already pointed out for cold neutron stars (e.g., [1][2][3][4]). On the other hand, the analyses on the protoneutron stars are very few [5][6][7][8].…”