Parametrized 3D models of neutrino-driven supernova explosions

Abstract

Time-dependent and direction-dependent neutrino and gravitational-wave (GW) signatures are presented for a set of three-dimensional (3D) hydrodynamic models of parametrized, neutrino-driven supernova explosions of non-rotating 15 and 20 M stars. We employed an approximate treatment of neutrino transport based on a gray spectral description and a ray-by-ray treatment of multi-dimensional effects. Owing to the excision of the high-density core of the proto-neutron star (PNS) and the use of an axis-free (Yin-Yang) overset grid, the models can be followed from the post-bounce accretion phase through the onset of the explosion into more than one second of the early cooling evolution of the PNS without imposing any symmetry restrictions and covering a full sphere. Gravitational waves and neutrino emission exhibit the generic time-dependent features already known from 2D (axi-symmetric) models. Violent non-radial hydrodynamic mass motions in the accretion layer and their interaction with the outer layers of the proto-neutron star together with anisotropic neutrino emission give rise to a GW signal with an amplitude of ∼5−20 cm in the frequency range of 100−500 Hz. The GW emission from mass motions usually reaches a maximum before the explosion sets in. After the onset of the explosion the GW signal exhibits a low-frequency modulation, in some cases describing a quasi-monotonic growth, associated with the non-spherical expansion of the explosion shock wave and the large-scale anisotropy of the escaping neutrino flow. Variations of the mass-quadrupole moment caused by convective activity inside the nascent neutron star add a high-frequency component to the GW signal during the post-explosion phase. The GW signals exhibit strong variability between the two polarizations, different explosion simulations and different observer directions, and besides common basic features do not possess any template character. The neutrino emission properties (fluxes and effective spectral temperatures) show fluctuations over the neutron star surface on spatial and temporal scales that reflect the different types of non-spherical mass motions in the supernova core, i.e., post-shock overturn flows and proto-neutron star convection. However, because very prominent, quasi-periodic sloshing motions of the shock caused by the standing accretion-shock instability are absent and the emission from different surface areas facing an observer adds up incoherently, the modulation amplitudes of the measurable neutrino luminosities and mean energies are significantly lower than predicted by 2D simulations.

Self-Sustained Asymmetry of Lepton-Number Emission: A New Phenomenon During the Supernova Shock-Accretion Phase in Three Dimensions

“…To evaluate the observational quantities we follow the procedure described in Sect. 3.1 of Müller, Janka, & Wongwathanarat (2012) and in Appendix A of Tamborra et al (2014) and calculate the observable flux, here the number-flux N, from the ray-by-ray-computed number-flux densities, F n (R), at points R on the radiating surface by an integration over the visible hemisphere, cf. Eq.…”

Observing gravitational waves from core-collapse supernovae in the advanced detector era

“…These include, but are not necessarily limited to, turbulent convection driven by negative entropy or lepton gradients and the SASI (e.g., [12][13][14]21,37]), rapidly rotating collapse and bounce (e.g., [17,39,75]), postbounce nonaxisymmetric rotational instabilities (e.g., [38,44,139,140]), rotating collapse to a black hole (e.g., [40]), asymmetric neutrino emission and outflows [12][13][14], and, potentially, rather extreme fragmentation-type instabilities occuring in accretion torii around nascent neutron stars or black holes [43]. A more extensive discussion of GW emission from CCSNe can be found in recent reviews on the subject in Refs.…”

“…We draw sample waveforms for GWs from nonrotating core collapse from the studies of Yakunin et al [14], Müller et al [37], and Ott et al [29]. Yakunin et al performed 2D simulations of neutrino-driven CCSNe.…”

“…The magnitude and time variation of deviations from spherical symmetry, and thus the strength of the emitted GW signal, are uncertain and likely vary from event to event [1,13]. State-of-the-art models, building upon an extensive body of theoretical work on the GW signature of CCSNe, predict GW strains-relative displacements of test masses in a detector on Earth-h of order 10 −23 -10 −20 for a core collapse event at 10 kpc, signal durations of 1 ms − few s, frequencies of ∼1 − few 1000 Hz, and total emitted energies E GW of 10 41 -10 47 erg (corresponding to 10 −12 − 10 −7 M ⊙ c 2 ) [1,13,14,17,27,29,[37][38][39][40]. More extreme phenomenological models, such as long-lasting rotational instabilities of the proto-neutron star and accretion disk fragmentation instabilities, associated with hypernovae and collapsars, suggest much larger strains and more energetic emission, with E GW perhaps up to 10 52 erg (∼0.01M ⊙ c 2 ) [41][42][43][44].…”

Inferring the core-collapse supernova explosion mechanism with gravitational waves

“…• Müller et al [70] performed 3D simulations of neutrino-driven CCSNe with gray neutrino transport and an inner boundary condition to prescribe the contraction of the proto-neutron star core. They started the simulations after core bounce and assumed a time-varying inner boundary, cutting out much of the proto-neutron star.…”