scholarly journals Rapid model comparison of equations of state from gravitational wave observation of binary neutron star coalescences

2021 ◽  
Vol 104 (8) ◽  
Author(s):  
Shaon Ghosh ◽  
Xiaoshu Liu ◽  
Jolien Creighton ◽  
Ignacio Magaña Hernandez ◽  
Wolfgang Kastaun ◽  
...  
Keyword(s):  
Neutron Star ◽  
Gravitational Wave ◽  
Model Comparison ◽  
Equations Of State ◽  
Binary Neutron Star ◽  
Wave Observation

scholarly journals Protomagnetar research through an analysis of the X-ray plateau in the multi-messengar era

2020 ◽  
Vol 641 ◽  
pp. A56
Author(s):  
Xiaoxiao Ren ◽  
Daming Wei ◽  
Zhenyu Zhu ◽  
Yan Yan ◽  
Chengming Li
Keyword(s):  
Neutron Star ◽  
Equation Of State ◽  
Gravitational Wave ◽  
Gamma Ray ◽  
Equations Of State ◽  
Electromagnetic Emission ◽  
Gamma Ray Bursts ◽  
Gamma Ray Burst ◽  
X Ray ◽  
Binary Neutron Star

The joint detection of the gravitational wave signal and the electromagnetic emission from a binary neutron star merger can place unprecedented constraint on the equation of state of supranuclear matter. Although a variety of electromagnetic counterparts have been observed for GW170817, including a short gamma-ray burst, kilonova, and the afterglow emission, the nature of the merger remnant is still unclear, however. The X-ray plateau is another important characteristics of short gamma-ray bursts. This plateau is probably due to the energy injection from a rapidly rotating magnetar. We investigate what we can learn from the detection of a gravitational wave along with the X-ray plateau. In principle, we can estimate the mass of the merger remnant if the X-ray plateau is caused by the central magnetar. We selected eight equations of state that all satisfy the constraint given by the gravitational wave observation, and then calculated the mass of the merger remnants of four short gamma-ray bursts with a well-measured X-ray plateau. If, on the other hand, the mass of the merger remnant can be obtained by gravitational wave information, then by comparing the masses derived by these two different methods can further constrain the equation of state. We discuss the possibility that the merger product is a quark star. In addition, we estimate the possible mass range for the recently discovered X-ray transient CDF-S XT2 that probably originated from a binary neutron star merger. Finally, under the assumption that the post-merger remnant of GW170817 was a supramassive neutron star, we estimated the allowed parameter space of the supramassive neutron star and find that in this case, the magnetic dipole radiation energy is so high that it may have some effects on the short gamma-ray burst and kilonova emission. The lack of detection of these effects suggests that the merger product of GW170817 may not be a supermassive neutron star.

scholarly journals A scalable random forest regressor for combining neutron-star equation of state measurements: a case study with GW170817 and GW190425

2020 ◽  
Vol 499 (4) ◽  
pp. 5972-5977
Author(s):  
Francisco Hernandez Vivanco ◽  
Rory Smith ◽  
Eric Thrane ◽  
Paul D Lasky
Keyword(s):  
Neutron Star ◽  
Equation Of State ◽  
Gravitational Wave ◽  
Learning Algorithm ◽  
Machine Learning Algorithm ◽  
Combine Data ◽  
Binary Neutron Star ◽  
Wave Measurements ◽  
Wave Observation

ABSTRACT Gravitational-wave observations of binary neutron star coalescences constrain the neutron-star equation of state by enabling measurement of the tidal deformation of each neutron star. This deformation is well approximated by the tidal deformability parameter Λ, which was constrained using the first binary neutron star gravitational-wave observation, GW170817. Now, with the measurement of the second binary neutron star, GW190425, we can combine different gravitational-wave measurements to obtain tighter constraints on the neutron-star equation of state. In this paper, we combine data from GW170817 and GW190425 to place constraints on the neutron-star equation of state. To facilitate this calculation, we derive interpolated marginalized likelihoods for each event using a machine learning algorithm. These likelihoods, which we make publicly available, allow for results from multiple gravitational-wave signals to be easily combined. Using these new data products, we find that the radius of a fiducial 1.4 M⊙ neutron star is constrained to $11.6^{+1.6}_{-0.9}$ km at 90 per cent confidence and the pressure at twice the nuclear saturation density is constrained to $3.1^{+3.1}_{-1.3}\times 10^{34}$ dyne cm−2 at 90 per cent confidence. Combining GW170817 and GW190425 produces constraints indistinguishable from GW170817 alone and is consistent with findings from other works.

scholarly journals Constraints on the neutron star equation of state from AT2017gfo using radiative transfer simulations

2018 ◽  
Vol 480 (3) ◽  
pp. 3871-3878 ◽  
Author(s):  
Michael W Coughlin ◽  
Tim Dietrich ◽  
Zoheyr Doctor ◽  
Daniel Kasen ◽  
Scott Coughlin ◽  
...  
Keyword(s):  
Neutron Star ◽  
Equation Of State ◽  
Gravitational Wave ◽  
Equations Of State ◽  
Source Parameters ◽  
Gaussian Process Regression ◽  
New Era ◽  
Electromagnetic Transient ◽  
Binary Neutron Star ◽  
Electromagnetic Measurements

ABSTRACT The detection of the binary neutron star merger GW170817 together with the observation of electromagnetic counterparts across the entire spectrum inaugurated a new era of multimessenger astronomy. In this study, we incorporate wavelength-dependent opacities and emissivities calculated from atomic-structure data enabling us to model both the measured light curves and spectra of the electromagnetic transient AT2017gfo. Best fits of the observational data are obtained by Gaussian Process Regression, which allows us to present posterior samples for the kilonova and source properties connected to GW170817. Incorporating constraints obtained from the gravitational wave signal measured by the LIGO-Virgo Scientific Collaboration, we present a $90{{\ \rm per\ cent}}$ upper bound on the mass ratio q ≲ 1.38 and a lower bound on the tidal deformability of $\tilde{\Lambda } \gtrsim 197$, which rules out sufficiently soft equations of state. Our analysis is a path-finder for more realistic kilonova models and shows how the combination of gravitational wave and electromagnetic measurements allow for stringent constraints on the source parameters and the supranuclear equation of state.

scholarly journals Waveform systematics in the gravitational-wave inference of tidal parameters and equation of state from binary neutron-star signals

2021 ◽  
Vol 103 (12) ◽  
Author(s):  
Rossella Gamba ◽  
Matteo Breschi ◽  
Sebastiano Bernuzzi ◽  
Michalis Agathos ◽  
Alessandro Nagar
Keyword(s):  
Neutron Star ◽  
Equation Of State ◽  
Gravitational Wave ◽  
Binary Neutron Star

scholarly journals Accelerated detection of the binary neutron star gravitational-wave background

2019 ◽  
Vol 100 (4) ◽  
Author(s):  
Francisco Hernandez Vivanco ◽  
Rory Smith ◽  
Eric Thrane ◽  
Paul D. Lasky
Keyword(s):  
Neutron Star ◽  
Gravitational Wave ◽  
Binary Neutron Star ◽  
Gravitational Wave Background

scholarly journals Fundamental physics and the absence of sub-millisecond pulsars

2018 ◽  
Vol 620 ◽  
pp. A69 ◽  
Author(s):  
B. Haskell ◽  
J. L. Zdunik ◽  
M. Fortin ◽  
M. Bejger ◽  
R. Wijnands ◽  
...  
Keyword(s):  
Neutron Star ◽  
Equation Of State ◽  
Neutron Stars ◽  
Gravitational Wave ◽  
Equations Of State ◽  
Rotation Frequency ◽  
Hadronic Matter ◽  
Spin Distribution ◽  
Test Models ◽  
State Of Matter

Context. Rapidly rotating neutron stars are an ideal laboratory to test models of matter at high densities. In particular, the maximum rotation frequency of a neutron star depends on the equation of state and can be used to test models of the interior. However, observations of the spin distribution of rapidly rotating neutron stars show evidence for a lack of stars spinning at frequencies higher than f ≈ 700 Hz, well below the predictions of theoretical equations of state. This has generally been taken as evidence of an additional spin-down torque operating in these systems, and it has been suggested that gravitational wave torques may be operating and be linked to a potentially observable signal. Aims. We aim to determine whether additional spin-down torques (possibly due to gravitational wave emission) are necessary, or if the observed limit of f ≈ 700 Hz could correspond to the Keplerian (mass-shedding) break-up frequency for the observed systems, and is simply a consequence of the currently unknown state of matter at high densities. Methods. Given our ignorance with regard to the true equation of state of matter above nuclear saturation densities, we make a minimal physical assumption and only demand causality, that is, that the speed of sound in the interior of the neutron star should be lower than or equal to the speed of light c. We then connected our causally limited equation of state to a realistic microphysical crustal equation of state for densities below nuclear saturation density. This produced a limiting model that gave the lowest possible maximum frequency, which we compared to observational constraints on neutron star masses and frequencies. We also compared our findings with the constraints on the tidal deformability obtained in the observations of the GW170817 event. Results. We rule out centrifugal breakup as the mechanism preventing pulsars from spinning faster than f ≈ 700 Hz, as the lowest breakup frequency allowed by our causal equation of state is f ≈ 1200 Hz. A low-frequency cutoff, around f ≈ 800 Hz could only be possible when we assume that these systems do not contain neutron stars with masses above M ≈ 2 M⊙. This would have to be due either to selection effects, or possibly to a phase transition in the interior of the neutron star that leads to softening at high densities and a collapse to either a black hole or a hybrid star above M ≈ 2 M⊙. Such a scenario would, however, require a somewhat unrealistically stiff equation of state for hadronic matter, in tension with recent constraints obtained from gravitational wave observations of a neutron star merger.

scholarly journals Measuring the eccentricity of GW170817 and GW190425

2020 ◽  
Vol 497 (2) ◽  
pp. 1966-1971 ◽  
Author(s):  
Amber K Lenon ◽  
Alexander H Nitz ◽  
Duncan A Brown
Keyword(s):  
Parameter Estimation ◽  
Neutron Star ◽  
Gravitational Wave ◽  
Matched Filter ◽  
Wave Frequency ◽  
Limited Information ◽  
Binary Neutron Star ◽  
Wave Emission

ABSTRACT Two binary neutron star mergers, GW170817 and GW190425, have been detected by Advanced LIGO and Virgo. These signals were detected by matched-filter searches that assume that the star’s orbit has circularized by the time their gravitational-wave emission is observable. This suggests that their eccentricity is low, but full parameter estimation of their eccentricity has not yet been performed. We use gravitational-wave observations to measure the eccentricity of GW170817 and GW190425. We find that the eccentricity at a gravitational-wave frequency of 10 Hz is e ≤ 0.024 and e ≤ 0.048 for GW170817 and GW190425, respectively (90 per cent confidence). This is consistent with the binaries being formed in the field, as such systems are expected to have circularized to e ≤ 10−4 by the time they reach the LIGO–Virgo band. Our constraint is a factor of 2 smaller that an estimate based on GW170817 being detected by searches that neglect eccentricity. However, we caution that we find significant prior dependence in our limits, suggesting that there is limited information in the signals. We note that other techniques used to constrain binary neutron star eccentricity without full parameter estimation may miss degeneracies in the waveform, and that for future signals, it will be important to perform full parameter estimation with accurate waveform templates.

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