Gravitational wave signatures from low-mode spiral instabilities in rapidly rotating supernova cores

Abstract

We study properties of gravitational waves (GWs) from rotating core-collapse of a 15M ⊙ star by performing three-dimensional general-relativistic hydrodynamic simulations with an approximate neutrino transport. By parametrically changing the precollapse angular momentum, we focus on the effects of rotation on the GW signatures in the early postbounce evolution. Regarding threeflavor neutrino transport, we solve the energy-averaged set of radiation energy and momentum based on the Thorne's momentum formalism. In addition to the gravitational quadrupole radiation from matter motions, we take into account GWs from anisotropic neutrino emission. With these computations, our results present several supporting evidences for the previous anticipation that non-axisymmetric instabilities play an essential role in determining the postbounce GW signatures.During prompt convection, we find that the waveforms show narrow-band and highly quasi-periodic signals which persist until the end of simulations. We point out that such feature reflects the growth of the one-armed spiral modes. The typical frequency of the quasi-periodic waveforms can be well explained by the propagating acoustic waves between the stalled shock and the rotating protoneutron star surface, which suggests the appearance of the standing-accretion-shock instability.Although the GW signals exhibit strong variability between the two polarizations and different observer directions, they are within the detection limits of next generation detectors such as by KAGRA and Advanced LIGO, if the source with sufficient angular momentum is located in our Galaxy. 95.85.Sz, 97.60.Bw

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

“…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].…”

“…Hayama et al [73] studied the detectability of GWs from multidimensional CCSN simulations from [38,[74][75][76]. Using the coherent network analysis network pipeline RIDGE [77], signals in simulated Gaussian noise for a four-detector network containing the two Advanced LIGO detectors, Advanced Virgo, and KAGRA are considered.…”

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

“…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].…”

Gravitational Wave Emission from Long-Term Self-Consistent Two-dimensional Core-Collapse Supernova Models

“…In the postbounce phase, a variety of GW emission processes have been proposed, including convection inside the proto-neutron star (PNS) and in the postshock region, the Standing-Accretion-Shock-Instability (SASI, [5,6]), and nonaxisymmetric instabilities [7]. But most of these previous work have employed a very limited set of progenitor models, so that the relation between the progenitors' characteristics (such as progenitors' compactness [8]) and the GW emission is not well understood yet.…”

“…We use the equation of state (EOS) by Lattimer & Swesty (1991) (incompressibility K = 220 MeV). We extract the GW signal from our simulations using the standard quadrupole formula (e.g., [7]). The angle between the symmetry axis in 2D simulations and the line of sight of the observer is taken to be π/2 to maximize the GW amplitude.…”