Parameter estimation of a two-component neutron star model with spin wandering

ABSTRACT It is an open challenge to estimate systematically the physical parameters of neutron star interiors from pulsar timing data while separating spin wandering intrinsic to the pulsar (achromatic timing noise) from measurement noise and chromatic timing noise (due to propagation effects). In this paper, we formulate the classic two-component, crust-superfluid model of neutron star interiors as a noise-driven, linear dynamical system and use a state-space-based expectation–maximization method to estimate the system parameters using gravitational-wave and electromagnetic timing data. Monte Carlo simulations show that we can accurately estimate all six parameters of the two-component model provided that electromagnetic measurements of the crust angular velocity and gravitational-wave measurements of the core angular velocity are both available. When only electromagnetic data are available, we can recover the overall relaxation time-scale, the ensemble-averaged spin-down rate, and the strength of the white-noise torque on the crust. However, the estimates of the secular torques on the two components and white-noise torque on the superfluid are biased significantly.

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Discriminating strange star mergers from neutron star mergers by gravitational-wave measurements

Physical Review D ◽

10.1103/physrevd.81.024012 ◽

2010 ◽

Vol 81 (2) ◽

Cited By ~ 43

Author(s):

A. Bauswein ◽

R. Oechslin ◽

H.-T. Janka

Keyword(s):

Neutron Star ◽

Gravitational Wave ◽

Strange Star ◽

Wave Measurements

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Ultra-Short Period Double-Degenerate Binaries

International Astronomical Union Colloquium ◽

10.1017/s0252921100002281 ◽

2004 ◽

Vol 190 ◽

pp. 324-337 ◽

Cited By ~ 7

Author(s):

Mark Cropper ◽

Gavin Ramsay ◽

Kinwah Wu ◽

Pasi Hakala

Keyword(s):

Neutron Star ◽

Gravitational Wave ◽

Orbital Period ◽

Binary Systems ◽

Star Model ◽

X Ray ◽

Compact Binaries ◽

Short Period ◽

Observational Status ◽

Strong Gravitational Wave

AbstractWe review the current observational status of the ROSAT sources RX J1914.4+2456 and RX J0806.3+1527, and the evidence that these are ultra-short period (< 10 min) binary systems. We argue that an Intermediate Polar interpretation can be ruled out, that they are indeed compact binaries with a degenerate secondary, and that the period seen in the X-ray and optical is the orbital period. A white dwarf primary is preferred, but a neutron star cannot be excluded. We examine the capability of the three current double-degenerate models (Polar, Direct Accretor and Electric Star) to account for the observational characteristics of these systems. All models have difficulties with some aspects of the observations, but none can be excluded with confidence at present. The Electric Star model provides the best description, but the lifetime of this phase requires further investigation. These ultra-short period binaries will be strong gravitational wave emitters in the LISA bandpass, and because of their known source properties will be important early targets for gravitational wave studies.

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

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa3243 ◽

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.

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Comparing inclination-dependent analyses of kilonova transients

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stab221 ◽

2021 ◽

Vol 502 (2) ◽

pp. 3057-3065

Author(s):

J Heinzel ◽

M W Coughlin ◽

T Dietrich ◽

M Bulla ◽

S Antier ◽

...

Keyword(s):

Bayesian Inference ◽

Neutron Star ◽

Gravitational Wave ◽

Inclination Angle ◽

Soft Constraints ◽

Parameter Inference ◽

Binary Neutron Star ◽

Wave Measurements ◽

Inclination Angles ◽

Optical Transient

ABSTRACT The detection of the optical transient AT2017gfo proved that binary neutron star mergers are progenitors of kilonovae (KNe). Using a combination of numerical-relativity and radiative-transfer simulations, the community has developed sophisticated models for these transients for a wide portion of the expected parameter space. Using these simulations and surrogate models made from them, it has been possible to perform Bayesian inference of the observed signals to infer properties of the ejected matter. It has been pointed out that combining inclination constraints derived from the KN with gravitational-wave measurements increases the accuracy with which binary parameters can be estimated, in particular breaking the distance-inclination degeneracy from gravitational wave inference. To avoid bias from the unknown ejecta geometry, constraints on the inclination angle for AT2017gfo should be insensitive to the employed models. In this work, we compare different assumptions about the ejecta and radiative reprocesses used by the community and we investigate their impact on the parameter inference. While most inferred parameters agree, we find disagreement between posteriors for the inclination angle for different geometries that have been used in the current literature. According to our study, the inclusion of reprocessing of the photons between different ejecta types improves the modeling fits to AT2017gfo and, in some cases, affects the inferred constraints. Our study motivates the inclusion of large ∼ 1-mag uncertainties in the KN models employed for Bayesian analysis to capture yet unknown systematics, especially when inferring inclination angles, although smaller uncertainties seem appropriate to capture model systematics for other intrinsic parameters. We can use this method to impose soft constraints on the ejecta geometry of the KN AT2017gfo.

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Probing modified gravitational-wave propagation through tidal measurements of binary neutron star mergers

Physical Review D ◽

10.1103/physrevd.103.124047 ◽

2021 ◽

Vol 103 (12) ◽

Author(s):

Nan Jiang ◽

Kent Yagi

Keyword(s):

Wave Propagation ◽

Neutron Star ◽

Gravitational Wave ◽

Binary Neutron Star

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

Physical Review D ◽

10.1103/physrevd.103.124015 ◽

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

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A Gravitational-Wave Perspective on Neutron-Star Seismology

Universe ◽

10.3390/universe7040097 ◽

2021 ◽

Vol 7 (4) ◽

pp. 97

Author(s):

Nils Andersson

Keyword(s):

Neutron Star ◽

Neutron Stars ◽

Gravitational Wave ◽

Fundamental Mode ◽

Compact Binaries

We provide a bird’s-eye view of neutron-star seismology, which aims to probe the extreme physics associated with these objects, in the context of gravitational-wave astronomy. Focussing on the fundamental mode of oscillation, which is an efficient gravitational-wave emitter, we consider the seismology aspects of a number of astrophysically relevant scenarios, ranging from transients (like pulsar glitches and magnetar flares), to the dynamics of tides in inspiralling compact binaries and the eventual merged object and instabilities acting in isolated, rapidly rotating, neutron stars. The aim is not to provide a thorough review, but rather to introduce (some of) the key ideas and highlight issues that need further attention.

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