scholarly journals Mapping the gravitational-wave sky with LISA: A bayesian spherical harmonic approach

2021 ◽  
Author(s):  
Sharan Banagiri ◽  
Alexander Criswell ◽  
Tommy Kuan ◽  
Vuk Mandic ◽  
Joseph D Romano ◽  
...  
Keyword(s):  
Angular Distribution ◽  
Gravitational Wave ◽  
White Dwarf ◽  
Spherical Harmonic ◽  
Simplified Model ◽  
Wave Power ◽  
Frequency Content ◽  
Mass Ratio ◽  
Angular Structure ◽  
Bayesian Algorithm

Abstract The millihertz gravitational-wave frequency band is expected to contain a rich symphony of signals with sources ranging from galactic white dwarf binaries to extreme mass ratio inspirals. Many of these gravitational-wave signals will not be individually resolvable. Instead, they will incoherently add to produce stochastic gravitational-wave confusion noise whose frequency content will be governed by the dynamics of the sources. The angular structure of the power of the confusion noise will be modulated by the distribution of the sources across the sky. Measurement of this structure can yield important information about the distribution of sources on galactic and extra-galactic scales, their astrophysics and their evolution over cosmic timescales. Moreover, since the confusion noise is part of the noise budget of LISA, mapping it will also be essential for studying resolvable signals. In this paper, we present a Bayesian algorithm to probe the angular distribution of the stochastic gravitational-wave confusion noise with LISA using a spherical harmonic basis. We develop a technique based on Clebsch-Gordan coefficients to mathematically constrain the spherical harmonics to yield a non-negative distribution, making them optimal for expanding the gravitational-wave power and amenable to Bayesian inference. We demonstrate these techniques using a series of simulations and analyses, including recovery of simulated distributed and localized sources of gravitational-wave power. We also apply this method to map the gravitational-wave foreground from galactic white-dwarfs using a simplified model of the galactic white dwarf distribution.

scholarly journals Coupling of dual mass-transferring white dwarf binaries as a variable gravitational-wave emitter

2020 ◽  
Vol 496 (4) ◽  
pp. 5575-5583
Author(s):  
Naoki Seto
Keyword(s):  
Gravitational Wave ◽  
Gravitational Waves ◽  
White Dwarf ◽  
Simplified Model ◽  
Model Parameters ◽  
Body System ◽  
Amplitude Variation ◽  
Synchronous State ◽  
Orbital Periods ◽  
Small Period

ABSTRACT We study evolution of a hierarchical four-body (2 + 2) system composed by a pair of mass-transferring white dwarf binaries. Applying a simplified model around the synchronous state of two inner orbital periods, we newly find that the four-body system could settle down to a limit cycle with a small period gap. The period gap generates an amplitude variation of emitted gravitational waves as a beat effect. Depending on model parameters, the beat period could be 1–10 yr and a large amplitude variation might be observed by space gravitational-wave detectors.

scholarly journals Gravitational Wave Glitches in Chaotic Extreme-Mass-Ratio Inspirals

2021 ◽  
Vol 126 (14) ◽  
Author(s):  
Kyriakos Destounis ◽  
Arthur G. Suvorov ◽  
Kostas D. Kokkotas
Keyword(s):  
Gravitational Wave ◽  
Mass Ratio

scholarly journals The gravitational wave emission of double white dwarf coalescences

2020 ◽  
Vol 20 (9) ◽  
pp. 137
Author(s):  
Ze-Cheng泽成 Zou邹 ◽  
Xiao-Long小龙 Zhou周 ◽  
Yong-Feng清敏 Huang黄
Keyword(s):  
Gravitational Wave ◽  
White Dwarf ◽  
Wave Emission

Long-term evolution of directional spectra of wind waves modelled by DNS and kinetic equations, and comparison with airborne measurements

2021 ◽  
Author(s):  
Sergei Annenkov ◽  
Victor Shrira ◽  
Leonel Romero ◽  
Ken Melville
Keyword(s):  
Angular Distribution ◽  
Kinetic Equation ◽  
Kinetic Theory ◽  
Wind Waves ◽  
Kinetic Equations ◽  
Spectral Peak ◽  
Angular Width ◽  
Angular Structure ◽  
Airborne Measurements ◽  
Steady Growth

<p>We consider the evolution of directional spectra of waves generated by constant and changing wind, modelling it by direct numerical simulation (DNS), based on the Zakharov equation. Results are compared with numerical simulations performed with the Hasselmann kinetic equation and the generalised kinetic equation, and with airborne measurements of waves generated by offshore wind, collected during the GOTEX experiment off the coast of Mexico. Modelling is performed with wind measured during the experiment, and the initial conditions are taken as the observed spectrum at the moment when wind waves prevail over swell after the initial part of the evolution.</p><p>Directional spreading is characterised by the second moment of the normalised angular distribution function, taken at selected wavenumbers relative to the spectral peak. We show that for scales longer than the spectral peak the angular spread predicted by the DNS is close to that predicted by both kinetic equations, but it underestimates the corresponding measured value, apparently due to the presence of swell. For the spectral peak and shorter waves, the DNS shows good agreement with the data. A notable feature is the steady growth of angular width at the spectral peak with time/fetch, in contrast to nearly constant width in the kinetic equations modelling. Dependence of angular width on wavenumber is shown to be much weaker than predicted by the kinetic equations. A more detailed consideration of the angular structure at the spectral peak at large fetches shows that the kinetic equations predict an angular distribution with a well-defined peak at the central angle, while the DNS reproduces the observed angular structure, with a flat peak over a range of angles.</p><p>In order to study in detail the differences between the predictions of the DNS and the kinetic equations modelling under idealised conditions, we also perform numerical simulations for the case of constant wind forcing. As in the previous case of forcing by real wind, the most striking difference between the kinetic equations and the DNS is the steady growth with time of angular width at the spectral peak, which is demonstrated by the DNS, but is not present in the modelling with the kinetic equations. We show that while the kinetic theory, both in the case of the Hasselmann equation and the generalised kinetic equation, predicts a relatively simple shape of the spectral peak, the DNS shows a more complicated structure, with a flat top and dependence of the peak position on angle. We discuss the approximations employed in the derivation of the kinetic theory and the possible causes of the found differences of directional structure.</p>

scholarly journals Modeling Tidal Effects in Accretion Discs

1997 ◽  
Vol 163 ◽  
pp. 335-338
Author(s):  
Patrick Godon
Keyword(s):  
Equation Of State ◽  
White Dwarf ◽  
Accretion Discs ◽  
Time Dependent ◽  
Two Dimensional ◽  
Mass Ratio ◽  
Tidal Effects ◽  
Azimuthal Mode ◽  
Polytropic Equation

AbstractA two-dimensional time-dependent spectral code is used for the study of tidal effects in accretion discs. A cool disc around a white dwarf (characteristic of CV systems) is modeled under the assumption of a polytropic equation of state and a standard alpha viscosity prescription. For a mass ratio q < 0.1 (considered here) and under the assumption of a reflective inner boundary, tidal effects induce an eccentric (m=l azimuthal) mode in the disc together with an elliptic (m=2 azimuthal) mode in the inner disc.

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