Bulletin of the American Physical Society
APS April Meeting 2010
Volume 55, Number 1
Saturday–Tuesday, February 13–16, 2010; Washington, DC
Session Q11: Gravitational Waves from Neutron Stars |
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Sponsoring Units: GGR Chair: Lee Lindblom, California Institute of Technology Room: Maryland C |
Monday, February 15, 2010 1:30PM - 1:42PM |
Q11.00001: Broadband Search for Continuous-Wave Gravitation Radiation with LIGO Vladimir Dergachev Isolated rotating neutron stars are expected to emit gravitational radiation of nearly constant frequency and amplitude. Searches for such radiation with the LIGO interferometers are underway, using data taken from LIGO's fifth science run and ongoing sixth science run. Because the gravitational wave signal amplitudes are thought to be extremely weak, long time integrations must be carried out to detect a signal. This is complicated by the motion of the Earth (daily rotation and orbital motion) which induces substantial modulations of detected frequency and amplitude that are highly dependent on source location. Large volumes of acquired data make this search computationally difficult. We present an algorithm called PowerFlux, used to account for these modulations, when summing power spectral density estimates incoherently over long time intervals. Latest results using data from the S5 run, as well as challenges and progress of the detection search, will be discussed as well. [Preview Abstract] |
Monday, February 15, 2010 1:42PM - 1:54PM |
Q11.00002: Nonlinear mode coupling in rotating neutron stars and its effects on the r-mode instability Ruxandra Bondarescu, Saul Teukolsky, Ira Wasserman This talk will focus on describing the nonlinear dynamics of the r-mode instability in rapidly rotating neutron stars. R-modes are oscillations in rotating fluids that occur due to the Coriolis effect. In fast rotators these modes can be driven unstable by the gravitational radiation backreaction force when gravitational driving dominates viscous damping. An unstable L=2, m=2 r-mode spins down a rotating neutron star by converting rotational energy into gravitational radiation and mode energy. It has been suggested that the r-mode instability can set a limiting frequency to accreting neutron stars. Nonlinear effects become important when a mode grows above its parametric instability threshold and excites other near resonant modes in the star. The duration of the instability and the amplitude at which the instability saturates depend on neutron star composition via viscous dissipation and neutrino cooling. In some scenarios r-modes may also lead to detectable gravitational radiation. [Preview Abstract] |
Monday, February 15, 2010 1:54PM - 2:06PM |
Q11.00003: Gravitational Waves from Low Mass Neutron Stars C.J. Horowitz Recently, using large scale molecular dynamics simulations, we determined that neutron star crust is very strong, some 10 billion times stronger than steel [1]. This makes star crust the strongest material known and it can support relatively large ``mountains''. These bumps on rapidly rotating neutron stars can radiate strong gravitational waves (GW). Therefore, we strongly encourage ongoing and future searches for continuous GW. In the present paper, we speculate that low mass neutron stars, although they may be difficult to produce, could be even stronger GW sources. We find that the crust can support very large ellipticities (fractional differences in moments of inertia) of 0.001 or even larger in low mass neutron stars. This is because a larger fraction of a low mass neutron star is solid crust compared to a 1.4 solar mass star and because the weaker gravity allows the crust to support even larger mountains. Therefore, if low mass neutron stars can be produced, for example via fragmentation during a neutron star merger, then they could produce very strong continuous gravitational waves. \\[4pt] [1] C. J. Horowitz and K. Kadau, Phys. Rev. Lett. 102:191102,2009. [Preview Abstract] |
Monday, February 15, 2010 2:06PM - 2:18PM |
Q11.00004: Quadrupole Moments of Rotating Neutron Stars Swapnil Tripathi A rotating stars oblateness creates a deformation in the gravitational field outside the star,which is measured by the quadrupole-moment tensor. In this work we make corrections to certain previous calculations of quadrupole moments of rotating neutron stars in the literature. We propose an EOS(equation of state) independent empirical relation for the quadrupole moment of rotating neutron stars. A quadrupole moment maximizing EOS is proposed and a formula found for the limit set by causality on the quadrupole moment of a star of fixed gravitational mass. [Preview Abstract] |
Monday, February 15, 2010 2:18PM - 2:30PM |
Q11.00005: Gravitational waves from NS-NS and NS-BH inspirals and the high-density equation of state John L. Friedman This talk reviews recent work by members of UWM's Center for Gravitational Physics and Cosmology and their collaborators on NS-NS and NS-BH inspiral. A parametrized equation of state is used to systematize the constraints imposed by observation on the equation of state of cold matter above nuclear density. Current NS-NS work involves: Determination of surfaces in the equation of state (EOS) parameter space associated with a given departure from the waveform of point-particle inspiral; using waveforms from numerical simulations to calibrate quasiequilibrium sequences and post-Newtonian waveforms; and development of improved initial data codes. Work on BH-NS inspiral includes simulations with an increased range of mass ratios and black-hole spins. [Preview Abstract] |
Monday, February 15, 2010 2:30PM - 2:42PM |
Q11.00006: Tidal deformability of neutron stars with realistic equations of state Benjamin Lackey, Tanja Hinderer, Jocelyn Read, Ryan Lang The low-frequency part of the gravitational wave signal of binary neutron star inspirals can potentially yield robust information on the nuclear equation of state. The influence of a star's internal structure on the waveform is characterized by a single parameter: the tidal deformability $\lambda$, which measures the star's quadrupole deformation in response to the companion's perturbing tidal field. We calculate $\lambda$ for a wide range of equations of state and find that the value of $\lambda$ spans an order of magnitude for the range of equation of state models considered. An analysis of the feasibility of discriminating between neutron star equations of state with gravitational wave observations of the early part of the inspiral reveals that the measurement error in $\lambda$ increases steeply with the total mass of the binary. Comparing the errors with the expected range of $\lambda$, we find that Advanced LIGO observations of binaries at a distance of 100~Mpc will probe only unusually stiff equations of state, while the proposed Einstein Telescope is likely to see a clean tidal signature. [Preview Abstract] |
Monday, February 15, 2010 2:42PM - 2:54PM |
Q11.00007: Tuning advanced gravitational-wave detectors to optimally measure neutron-star merger waves Leo Stein Next-generation gravitational wave detectors have the potential to bring us astrophysical information in yet unexplored regimes. One of the possibilities is learning about neutron stars' equations of state from the gravitational wave burst of a binary coalescence. Since these events are ``bursty'', one does not have the luxury of time-averaging to improve S/N; one can only hope to do better by ``tuning'' a detector network to have the noise performance which will be most informative about the physics. We present a Bayesian method for optimizing a detector network given a prior distribution of physical parameters which affect the gravitational wave signal. Each detection adds information about the parameter distribution, updating the posterior and the optimal detector configuration. We demonstrate the algorithm with toy signal and detector response models and predict whether tuning Advanced LIGO (via the signal recycling cavity) will be fruitful in accelerating our understanding of neutron stars through their mergers. [Preview Abstract] |
Monday, February 15, 2010 2:54PM - 3:06PM |
Q11.00008: Modeling Gravitational Wave Emission from Soft Gamma Repeaters Christian D. Ott, Peter Kalmus Soft gamma repeaters and anomalous x-ray pulsars are thought to be magnetars: neutron stars with extreme magnetic fields. When active they sporadically emit sudden bursts of soft gamma rays. The majority of these bursts have total energies of $10^{42}$~erg or less (isotropic), but three ``giant flares'' have had measured energies between $10^{45}$ and $10^{47}$ ergs. We perform 3D, fully general relativistic hydrodynamics simulations to model the gravitational wave (GW) emission due to global neutron star pulsational modes that may be excited during a burst. We discuss the relevant parameter space and connect our results to recent searches for GW from magnetars performed by the interferometric GW observatories. [Preview Abstract] |
Monday, February 15, 2010 3:06PM - 3:18PM |
Q11.00009: Gravitational Waves from Core-Collapse Supernova using CHIMERA: Analysis of the Gravitational Signatures Konstantin Yakunin, Pedro Marronetti, Stephen Bruenn, John Blondin, Austin Chertkow, Charlotte Dirk, William R. Hix, Eric Lentz, O.E. Bronson Messer, Anthony Mezzacappa Gravitational radiation, together with neutrino radiation, is the most important observational tool for understanding the dynamics of the central region of core-collapse supernova explosions. With the advent of the next generation of gravitational wave observatories such as Advanced LIGO, it is imperative to gain insight on how these signals are generated. We present the analysis of gravitational radiation corresponding to axisymmetric simulations performed with the CHIMERA code with emphasis in the origin of each part of the wavetrains and their interpretation in the framework of the collapse dynamics. [Preview Abstract] |
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