Measuring the angular momentum distribution in core-collapse supernova progenitors with gravitational waves

Abstract

The late collapse, core bounce, and the early postbounce phase of rotating core collapse leads to a characteristic gravitational wave (GW) signal. The precise shape of the signal is governed by the interplay of gravity, rotation, nuclear equation of state (EOS), and electron capture during collapse. We explore the detailed dependence of the signal on total angular momentum and its distribution in the progenitor core by means of a large set of axisymmetric general-relativistic hydrodynamics core collapse simulations, in which we systematically vary the initial angular momentum distribution in the core. Our simulations include a microphysical finite-temperature EOS, an approximate electron capture treatment during collapse, and a neutrino leakage scheme for the postbounce evolution. Our results show that the total angular momentum of the inner core at bounce and the inner core's ratio of rotational kinetic energy to gravitational energy T /|W | are both robust parameters characterizing the GW signal. We find that the precise distribution of angular momentum is relevant only for very rapidly rotating cores with T /|W | 8% at bounce. We construct a numerical template bank from our baseline set of simulations, and carry out additional simulations to generate trial waveforms for injection into simulated Advanced LIGO noise at a fiducial galactic distance of 10 kpc. Using matched filtering, we show that for an optimally-oriented source and Gaussian noise, Advanced LIGO could measure the total angular momentum to within ±20%, for rapidly rotating cores. For most waveforms, the nearest known degree of precollapse differential rotation is correctly inferred by both our matched filtering analysis and an alternative Bayesian model selection approach. We test our results for robustness against systematic uncertainties by injecting waveforms from simulations utilizing a different EOS and and variations in the electron fraction in the inner core. The results of these tests show that these uncertainties significantly reduce the accuracy with which the total angular momentum and its precollapse distribution can be inferred from observations.

Inferring the core-collapse supernova explosion mechanism with gravitational waves

“…Due to this, convection is inhibited in these regions, and the GW signature of turbulent convection characteristic of non-rotating core collapse is not present. For slowly rotating core collapse, prompt convection may contribute to the GW signal on timescales of tens of ms [48,54]. Typically, the peak GW strain from rotating core collapse is ∼ 10 −21 − 10 −20 for a source at 10 kpc, and emitted energy in GWs (E GW ) is ∼ 10 −10 − 10 −8 M .…”

“…• Abdikamalov et al [54] performed axisymmetric general-relativistic hydrodynamics simulations. A 15 M progenitor star was used, and the LattimerSwesty EOS with K = 220 MeV employed [57].…”

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

“…There are significant uncertainties in these and it is difficult to exactly predict the time series of the GW signal. Nevertheless, work by several authors [11,16,20,[149][150][151][152] has demonstrated that GW emission from rotating core collapse and bounce has robust features that can be identified and used to infer properties of the progenitor core.…”

First targeted search for gravitational-wave bursts from core-collapse supernovae in data of first-generation laser interferometer detectors

“…Such asymmetric dynamics are expected to be present in the pre-explosion stalledshock phase of CCSNe and may be crucial to the CCSN explosion mechanism (see, e.g., [14][15][16][17]). GWs can serve as probes of the magnitude and character of these asymmetries and thus may help in constraining the CCSN mechanism [18][19][20].…”

“…Early analytic and semi-analytic estimates of the GW signature of stellar collapse and CCSNe (e.g., [22][23][24][25][26]) gave optimistic signal strengths, suggesting that first-generation laser interferometer detectors could detect GWs from CCSNe in the Virgo cluster (at distances D 10 Mpc). Modern detailed multi-dimensional CCSN simulations (see, e.g., [20,[27][28][29][30][31][32][33][34][35] and the reviews in [36][37][38]) find GW signals of short duration ( 1 s) and emission frequencies in the most sensitive ∼10 − 2000 Hz band of ground based laser interferometer detectors. Predicted total emitted GW energies are in the range 10 −12 − 10 −8 M c 2 for emission mechanisms and progenitor parameters that are presently deemed realistic.…”