A New Multi-Dimensional General Relativistic Neutrino Hydrodynamics Code of Core-Collapse Supernovae. Iii. Gravitational Wave Signals From Supernova Explosion Models

Abstract

We present a detailed theoretical analysis of the gravitational-wave (GW) signal of the post-bounce evolution of core-collapse supernovae (SNe), employing for the first time relativistic, two-dimensional (2D) explosion models with multi-group, three-flavor neutrino transport based on the ray-by-ray-plus approximation. The waveforms reflect the accelerated mass motions associated with the characteristic evolutionary stages that were also identified in previous works: A quasi-periodic modulation by prompt postshock convection is followed by a phase of relative quiescence before growing amplitudes signal violent hydrodynamical activity due to convection and the standing accretion shock instability during the accretion period of the stalled shock. Finally, a high-frequency, low-amplitude variation from proto-neutron star (PNS) convection below the neutrinosphere appears superimposed on the low-frequency trend associated with the aspherical expansion of the SN shock after the onset of the explosion. Relativistic effects in combination with detailed neutrino transport are shown to be essential for quantitative predictions of the GW frequency evolution and energy spectrum, because they determine the structure of the PNS surface layer and its characteristic g-mode frequency. Burst-like high-frequency activity phases, correlated with sudden luminosity increase and spectral hardening of electron (anti-)neutrino emission for some 10 ms, are discovered as new features after the onset of the explosion. They correspond to intermittent episodes of anisotropic accretion by the PNS in the case of fallback SNe. We find stronger signals for more massive progenitors with large accretion rates. The typical frequencies are higher for massive PNSs, though the time-integrated spectrum also strongly depends on the model dynamics.

Quasi-Periodic Gravitational-Wave Emission due to the SASI Motion

“…Regarding the GWs, we have also confirmed previously reported emissions originated from the PNS surface g-mode oscillation [4]. For this emission, we found a dependence on the nuclear EoS.…”

“…(17) in [4], we overplot F peak in lower panels (black line). In both models F peak indeed tracks spectral peak quite well which argues for that the component "A" is originated from the g-mode oscillation of the PNS surface [4]. The component "B" is the newly found signal and is found only in SFHx which uses the softest nuclear EoS.…”

“…Traditionally most of the theoretical predictions have focused on the GW signals from rotational core collapse and bounce (see, e.g., [2,3]). While in the non-rotating core model, the evolution of convective activities in the PNS surface regions are considered to be the primal emission mechanism as a result of the g-mode oscillation, whose frequency appears at relatively high region (∼ 500 − 1000 Hz) depending on the PNS surface properties [4].…”

Systematic features of axisymmetric neutrino-driven core-collapse supernova models in multiple progenitors

“…For more massive progenitors with iron core, multi-dimensional (multi-D) effects such as neutrino-driven convection (e.g., Bethe 1990;Herant et al 1994;Burrows et al 1995;Janka & Müller 1996;Müller & Janka 1997) and the standing-accretion-shock-instability (SASI, Blondin et al 2003;Foglizzo et al 2006;Foglizzo et al 2007;Ohnishi et al 2006;Blondin & Mezzacappa 2007;Iwakami et al 2008;Iwakami et al 2009;Fernández & Thompson 2009;Hanke et al 2012; 2012; Couch 2013;Fernández et al 2014, see Foglizzo et al 2015 for a review) have been suggested to help the onset of the neutrino-driven explosion. Recently this has been confirmed by a number of self-consistent two-(2D) and three-dimensional (3D) simulations (e.g., Buras et al 2006;Ott et al 2008;Marek & Janka 2009;Bruenn et al 2013;Suwa et al 2010;Suwa et al 2014;Müller et al 2012a;Müller et al 2013;Takiwaki et al 2012;Takiwaki et al 2014;Hanke et al 2013;Dolence et al 2014;Bruenn et al 2014;Müller & Janka 2014, see Mezzacappa et al 2015Burrows 2013;Kotake et al 2012 for recent review)). Up to now, the number of these stateof-the-art models amounts to ∼ 40 covering the zero-age main sequence (ZAMS) mass from 8.1 M ⊙ (Müller et al 2012a) to 27 M ⊙ …”

Protoneutron Star Properties via Gravitational Wave Asteroseismology

“…With respect to the characteristic gravitational waves after the core bounce of core-collapse supernovae, the excitation of g-mode around the protoneutron star due to the standing accretion-shock instability and convection has been suggested from the numerical simulation [10], where the frequencies can be expressed as a function of M PNS /R 2 PNS . Thus, the dependence of the g-mode frequencies are different from that of the f -mode frequencies.…”