Gravitational waves and mass ejecta from binary neutron star mergers: Effect of large eccentricities

As current gravitational wave (GW) detectors increase in sensitivity, and particularly as new instruments are being planned, there is the possibility that ground-based GW detectors will observe GWs from highly eccentric neutron star binaries. We present the first detailed study of highly eccentric BNS systems with full (3+1)D numerical relativity simulations using consistent initial conditions, i.e., setups which are in agreement with the Einstein equations and with the equations of general relativistic hydrodynamics in equilibrium. Overall, our simulations cover two different equations of state (EOSs), two different spin configurations, and three to four different initial eccentricities for each pairing of EOS and spin. We extract from the simulated waveforms the frequency of the f-mode oscillations induced during close encounters before the merger of the two stars. The extracted frequency is in good agreement with f-mode oscillations of individual stars for the irrotational cases, which allows an independent measure of the supranuclear equation of state not accessible for binaries on quasicircular orbits. The energy stored in these f-mode oscillations can be as large as 10−3  M⊙∼1051  erg, even with a soft EOS. In order to estimate the stored energy, we also examine the effects of mode mixing due to the stars’ offset from the origin on the f-mode contribution to the GW signal. While in general (eccentric) neutron star mergers produce bright electromagnetic counterparts, we find that for the considered cases with fixed initial separation the luminosity decreases when the eccentricity becomes too large, due to a decrease of the ejecta mass. Finally, the use of consistent initial configurations also allows us to produce high-quality waveforms for different eccentricities which can be used as a test bed for waveform model development of highly eccentric binary neutron star systems.S. V. C. was supported by the DFG Research Training Group 1523/2 “Quantum and Gravitational Fields.” T. D. acknowledges support by the European Union’s Horizon 2020 research and innovation program under Grant Agreement No. 749145, BNSmergers. N. K. J.-M. acknowledges support from STFC Consolidator Grant No. ST/L000636/1. B. B. was supported by DFG Grant No. BR 2176/5-1. W. T. was supported by the National Science Foundation under Grant No. PHY-1707227. Also, this work has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie Grant Agreement No. 690904. This research was supported in part by Perimeter Institute for Theoretical Physics. Research at Perimeter Institute is supported by the Government of Canada through Industry Canada and by the Province of Ontario through the Ministry of Economic Development & Innovation. Computations were performed on the supercomputer SuperMUC at the LRZ (Munich) under the project number pr48pu and on the ARA cluster of the University of Jena

Constraints on Kerr-Newman black holes from merger-ringdown gravitational-wave observations

We construct a template to model the post-merger phase of a binary black hole coalescence in the presence of a remnant $U(1)$ charge. We include the quasi-normal modes typically dominant during a binary black hole coalescence, $(\ell,m,n) = \{(2,2,0), (2,2,1)\}$ and also present analytical fits for the quasinormal mode frequencies of a Kerr-Newman black hole in terms of its spin and charge, here also including the $(3,3,0)$ mode. Aside from astrophysical electric charge, our template can accommodate extensions of the Standard Model, such as a dark photon. Applying the model to LIGO-Virgo detections, we find that we are unable to distinguish between the charged and uncharged hypotheses from a purely post-merger analysis of the current events. However, restricting the mass and spin to values compatible with the analysis of the full signal, we obtain a 90th percentile bound $\bar{q} < 0.33$ on the black hole charge-to-mass ratio, for the most favorable case of GW150914. Under similar assumptions, by simulating a typical loud signal observed by the LIGO-Virgo network at its design sensitivity, we assess that this model can provide a robust measurement of the charge-to-mass ratio only for values $\bar{q} \gtrsim 0.5$; here we also assume that the mode amplitudes are similar to the uncharged case in creating our simulated signal. Lower values, down to $\bar{q} \sim 0.3$, could instead be detected when evaluating the consistency of the pre-merger and post-merger emission.Comment: 21 pages, 11 figures, 4 tables. Matches published versio

Gravitational waves from single neutron stars: an advanced detector era survey

With the doors beginning to swing open on the new gravitational wave astronomy, this review provides an up-to-date survey of the most important physical mechanisms that could lead to emission of potentially detectable gravitational radiation from isolated and accreting neutron stars. In particular we discuss the gravitational wave-driven instability and asteroseismology formalism of the f- and r-modes, the different ways that a neutron star could form and sustain a non-axisymmetric quadrupolar "mountain" deformation, the excitation of oscillations during magnetar flares and the possible gravitational wave signature of pulsar glitches. We focus on progress made in the recent years in each topic, make a fresh assessment of the gravitational wave detectability of each mechanism and, finally, highlight key problems and desiderata for future work.Comment: 39 pages, 12 figures, 2 tables. Chapter of the book "Physics and Astrophysics of Neutron Stars", NewCompStar COST Action 1304. Minor corrections to match published versio

Gravitational Waves and Gamma-Rays from a Binary Neutron Star Merger: GW170817 and GRB 170817A

On 2017 August 17, the gravitational-wave event GW170817 was observed by the Advanced LIGO and Virgo detectors, and the gamma-ray burst (GRB) GRB 170817A was observed independently by the Fermi Gamma-ray Burst Monitor, and the Anti-Coincidence Shield for the Spectrometer for the International Gamma-Ray Astrophysics Laboratory. The probability of the near-simultaneous temporal and spatial observation of GRB 170817A and GW170817 occurring by chance is $5.0\times {10}^{-8}$. We therefore confirm binary neutron star mergers as a progenitor of short GRBs. The association of GW170817 and GRB 170817A provides new insight into fundamental physics and the origin of short GRBs. We use the observed time delay of $(+1.74\pm 0.05)\,{\rm{s}}$ between GRB 170817A and GW170817 to: (i) constrain the difference between the speed of gravity and the speed of light to be between $-3\times {10}^{-15}$ and $+7\times {10}^{-16}$ times the speed of light, (ii) place new bounds on the violation of Lorentz invariance, (iii) present a new test of the equivalence principle by constraining the Shapiro delay between gravitational and electromagnetic radiation. We also use the time delay to constrain the size and bulk Lorentz factor of the region emitting the gamma-rays. GRB 170817A is the closest short GRB with a known distance, but is between 2 and 6 orders of magnitude less energetic than other bursts with measured redshift. A new generation of gamma-ray detectors, and subthreshold searches in existing detectors, will be essential to detect similar short bursts at greater distances. Finally, we predict a joint detection rate for the Fermi Gamma-ray Burst Monitor and the Advanced LIGO and Virgo detectors of 0.1-1.4 per year during the 2018-2019 observing run and 0.3-1.7 per year at design sensitivity

Observation of Gravitational Waves from a Binary Black Hole Merger

On September 14, 2015 at 09:50:45 UTC the two detectors of the Laser Interferometer Gravitational-Wave Observatory simultaneously observed a transient gravitational-wave signal. The signal sweeps upwards in frequency from 35 to 250 Hz with a peak gravitational-wave strain of 1.0 × 10−21. It matches the waveform predicted by general relativity for the inspiral and merger of a pair of black holes and the ringdown of the resulting single black hole. The signal was observed with a matched-filter signal-to-noise ratio of 24 and a false alarm rate estimated to be less than 1 event per 203 000 years, equivalent to a significance greater than 5.1σ. The source lies at a luminosity distance of 410þ160 −180 Mpc corresponding to a redshift z ¼ 0.09þ0.03 −0.04 . In the source frame, the initial black hole masses are 36þ5 −4M⊙ and 29þ4 −4M⊙, and the final black hole mass is 62þ4 −4M⊙, with 3.0þ0.5 −0.5M⊙c2 radiated in gravitational waves. All uncertainties define 90% credible intervals. These observations demonstrate the existence of binary stellar-mass black hole systems. This is the first direct detection of gravitational waves and the first observation of a binary black hole merger

Poisson Summation Formula in Hardy Spaces Hp(TΓ)H^p(T_\Gamma ) H p ( T Γ ) , p∈(0,1]p\in (0,1] p ∈ ( 0 , 1 ]

The Poisson summation formula for Hardy spaces Hp(TΓ) in tubes TΓ⊂ Cn for p∈ (0 , 1 ] is obtained. Unlike the case of Lp(Rn) spaces, the formula holds everywhere in TΓ without any additional assumptions. To the best of our knowledge, the result is new even for the univariate case—Hardy spaces in the upper half-plane