Gravitational waves and mass ejecta from binary neutron star mergers: Effect of the stars’ rotation

Abstract

We present new (3+1) dimensional numerical relativity simulations of the binary neutron star (BNS) mergers that take into account the NS spins. We consider different spin configurations, aligned or antialigned to the orbital angular momentum, for equal and unequal mass BNS and for two equations of state. All the simulations employ quasiequilibrium circular initial data in the constant rotational velocity approach, i.e. they are consistent with Einstein equations and in hydrodynamical equilibrium. We study the NS rotation effect on the energetics, the gravitational waves (GWs) and on the possible electromagnetic (EM) emission associated to dynamical mass ejecta. For dimensionless spin magnitudes of χ ∼ 0.1 we find that both spin-orbit interactions and spin-induced-quadrupole deformations affect the late-inspiral-merger dynamics. The latter is, however, dominated by finite-size effects. Spin (tidal) effects contribute to GW phase differences up to ∼ 5 (20) radians accumulated during the last eight orbits to merger. Similarly, after merger the collapse time of the remnant and the GW spectrogram are affected by the NSs rotation. Spin effects in dynamical ejecta are clearly observed in unequal mass systems in which mass ejection originates from the tidal tail of the companion. Consequently kilonovae and other EM counterparts are affected by spins. We find that spin aligned to the orbital angular momentum leads to brighter EM counterparts than antialigned spin with luminosities up to a factor of two higher.

Simulating Binary Neutron Stars with Hybrid Equation of States: Gravitational Waves, Electromagnetic Signatures and Challenges for Numerical Relativity

“…It is important to point out that for similar resolutions, cf. [70,71], the dephasing and consequently the shift in the merger time between similar resolutions have been significantly smaller for EoSs without phase transition. The bottom panel of Fig.…”

Kilohertz gravitational waves from binary neutron star remnants: Time-domain model and constraints on extreme matter

“…Two coupling frequencies are identified from secondary peaks of the spectra, see e.g. [21,22,73,74] (and figures below in this paper); we indicate them asf 2±0 following the notation of [24]. Although we will often refer to discrete frequencies (spectral peaks), we stress that the GW frequency is not constant but evolves (chirp-like) as the remnant becomes more compact and eventually collapses (see SLy data in Fig.…”

“…KiloHertz GWs contain the imprint of the merger remnant dynamics. The main signature is a short GW transient peaking at a few characteristic frequencies, the dominant one being associated with twice the rotation frequency of the remnant NS at f 2 > f mrg [16,[21][22][23][24][25][26][27][28][29][30]. The transient is more luminous for short-lived remnant than for longlived; an absolute upper limit to the energy per unit mass is 0.126( M 2.8M ) M c 2 , where M is the binary mass [12].…”

Search for Post-merger Gravitational Waves from the Remnant of the Binary Neutron Star Merger GW170817

“…For example, short-lived hypermassive NSs are expected to emit a few percent of a solar mass in GW energy (e.g., see the two lower dashed lines in Figure 1 that represent 1% and 10% of a solar mass; Kiuchi et al 2009;Clark et al 2014;Bernuzzi et al 2015b;Endrizzi et al 2016;Dietrich et al 2017aDietrich et al , 2017bFeo et al 2017), while our minimum 50% efficiency is   E M c 4.8 Corsi & Mészáros 2009). Figure 1 shows the h rss 50% for the considered waveform models as a function of the waveform's signal-weighted frequency.…”