[1007.4820] Fast Fisher Matrices and Lazy Likelihoods

Authors: Neil J. Cornish

Date: 27 Jul 2010

Abstract: Theoretical studies in gravitational wave astronomy often require the calculation of Fisher Information Matrices and Likelihood functions, which in a direct approach entail the costly step of computing gravitational waveforms. Here I describe an alternative technique that sidesteps the need to compute full waveforms, resulting in significant computational savings. I describe how related techniques can be used to speed up Bayesian inference applied to real gravitational wave data.

abs pdf

Jul 30, 2010

1007.4820 (/preprints)
2010-07-30, 00:34 [edit]


[1007.4789] Black-hole binaries with non-precessing spins

Authors: Mark Hannam, Sascha Husa, Frank Ohme, Doreen Mueller, Bernd Bruegmann

Date: 27 Jul 2010

Abstract: We present gravitational waveforms for the last orbits and merger of black-hole-binary (BBH) systems along two branches of the BBH parameter space: equal-mass binaries with equal non-precessing spins, and nonspinning unequal-mass binaries. The waveforms are calculated from numerical solutions of Einstein's equations for black-hole binaries that complete between six and ten orbits before merger. Along the equal-mass spinning branch, the spin parameter of each BH is $\chi_i = S_i/M_iˆ2 \in [-0.85,0.85]$, and along the unequal-mass branch the mass ratio is $q =M_2/M_1 \in [1,4]$. We discuss the construction of low-eccentricity puncture initial data for these cases, the properties of the final merged BH, and compare the last 8-10 GW cycles up to $M\omega = 0.1$ with the phase and amplitude predicted by standard post-Newtonian (PN) approximants. As in previous studies, we find that the phase from the 3.5PN TaylorT4 approximant is most accurate for nonspinning binaries. For equal-mass spinning binaries the 3.5PN TaylorT1 approximant (including spin terms up to only 2.5PN order) gives the most robust performance, but it is possible to treat TaylorT4 in such a way that it gives the best accuracy for spins $\chi_i > -0.75$. When high-order amplitude corrections are included, the PN amplitude of the $(\ell=2,m=\pm2)$ modes is larger than the NR amplitude by between 2-4%.

abs pdf

Jul 28, 2010

1007.4789 (/preprints)
2010-07-28, 10:50 [edit]


[1007.4298] Generalized Schwarzschild's method

Authors: Mir Abbas Jalali, Scott Tremaine

Date: 25 Jul 2010

Abstract: We describe a new finite element method (FEM) to construct continuous equilibrium distribution functions of stellar systems. The method is a generalization of Schwarzschild's orbit superposition method from the space of discrete functions to continuous ones. In contrast to Schwarzschild's method, FEM produces a continuous distribution function (DF) and satisfies the intra element continuity and Jeans equations. The method employs two finite-element meshes, one in configuration space and one in action space. The DF is represented by its values at the nodes of the action-space mesh and by interpolating functions inside the elements. The Galerkin projection of all equations that involve the DF leads to a linear system of equations, which can be solved for the nodal values of the DF using linear or quadratic programming, or other optimization methods. We illustrate the superior performance of FEM by constructing ergodic and anisotropic equilibrium DFs for spherical stellar systems (Hernquist models). We also show that explicitly constraining the DF by the Jeans equations leads to smoother and/or more accurate solutions with both Schwarzschild's method and FEM.

abs pdf

Jul 26, 2010

1007.4298 (/preprints)
2010-07-26, 23:08 [edit]


[1007.4213] Intrinsic selection biases of ground-based gravitational wave searches for high-mass BH-BH mergers

Authors: Richard O'Shaughnessy (1,4), Birjoo Vaishnav (2), James Healy (3), Deirdre Shoemaker (3) ((1) Center for Gravitational Wave Physics, Penn State University, (2) Center for Gravitational Wave Astronomy, The University of Texas at Brownsville, (3) Center for Relativistic Astrophysics, Georgia Tech, (4) Center for Gravitation and Cosmology, University of Wisconsin-Milwaukee)

Date: 23 Jul 2010

Abstract: The next generation of ground-based gravitational wave detectors may detect a few mergers of comparable-mass M\simeq 100-1000 Msun ("intermediate-mass'', or IMBH) spinning black holes. Black hole spin is known to have a significant impact on the orbit, merger signal, and post-merger ringdown of any binary with non-negligible spin. In particular, the detection volume for spinning binaries depends significantly on the component black hole spins. We provide a fit to the single-detector and isotropic-network detection volume versus (total) mass and arbitrary spin for equal-mass binaries. Our analysis assumes matched filtering to all significant available waveform power (up to l=6 available for fitting, but only l<= 4 significant) estimated by an array of 64 numerical simulations with component spins as large as S_{1,2}/Mˆ2 <= 0.8. We provide a spin-dependent estimate of our uncertainty, up to S_{1,2}/Mˆ2 <= 1. For the initial (advanced) LIGO detector, our fits are reliable for $M\in[100,500]M_\odot$ ($M\in[100,1600]M_\odot$). In the online version of this article, we also provide fits assuming incomplete information, such as the neglect of higher-order harmonics. We briefly discuss how a strong selection bias towards aligned spins influences the interpretation of future gravitational wave detections of IMBH-IMBH mergers.

abs pdf

Jul 26, 2010

1007.4213 (/preprints)
2010-07-26, 23:07 [edit]


[1007.4203] Black hole-neutron star mergers: effects of the orientation of the black hole spin

Authors: Francois Foucart, Matthew D. Duez, Lawrence E. Kidder, Saul A. Teukolsky

Date: 23 Jul 2010

Abstract: The spin of black holes in black hole-neutron star (BHNS) binaries can have a strong influence on the merger dynamics and the postmerger state; a wide variety of spin magnitudes and orientations are expected to occur in nature. In this paper, we report the first simulations in full general relativity of BHNS mergers with misaligned black hole spin. We vary the spin magnitude from a/m=0 to a/m=0.9 for aligned cases, and we vary the misalignment angle from 0 to 80 degrees for a/m=0.5. We restrict our study to 3:1 mass ratio systems and use a simple Gamma-law equation of state. We find that the misalignment angle has a strong effect on the mass of the postmerger accretion disk, but only for angles greater than ~ 40 degrees. Although the disk mass varies significantly with spin magnitude and misalignment angle, we find that all disks have very similar lifetimes ~ 100ms. Their thermal and rotational profiles are also very similar. For a misaligned merger, the disk is tilted with respect to the final black hole's spin axis. This will cause the disk to precess, but on a timescale longer than the accretion time. In all cases, we find promising setups for gamma-ray burst production: the disks are hot, thick, and hyperaccreting, and a baryon-clear region exists above the black hole.

abs pdf

Jul 26, 2010

1007.4203 (/preprints)
2010-07-26, 23:07 [edit]


[1007.4351] NP Stokes fields for radio astronomy

Authors: Ezra T. Newman, Richard H. Price

Date: 25 Jul 2010

Abstract: The spin weighted spherical harmonic (SWSH) description of angular functions typically is associated with the Newman-Penrose (NP) null tetrad formalism. Recently the SWSH description, but not the NP formalism, has been used in the study of the polarization anisotropy of the cosmic microwave background. Here we relate this application of SWSHs to a description of electromagnetic radiation and polarization in the NP formalism. In particular we introduce NP Stokes fields that are the NP equivalent of the Stokes parameters. In addition to giving a more coherent foundation for the recent cosmological SWSH application, the NP formalism aids in the computation of the Lorentz transformation properties of polarization.

abs pdf

Jul 26, 2010

1007.4351 (/preprints)
2010-07-26, 23:07 [edit]


[1007.4289] Using temporal distributions of transient events to characterize cosmological source populations

Authors: E. Howell, D. Coward, R. Burman, D. Blair

Date: 25 Jul 2010

Abstract: The brightest events in a time series of cosmological transients obey an observation time dependence which is often overlooked. This dependence can be exploited to probe the global properties of electromagnetic and gravitational wave transients (Howell et al. 2007a, Coward & Burman 2005). We describe a new relation based on a peak flux--observation time distribution and show that it is invariant to the luminosity distribution of the sources (Howell et al. 2007b). Applying this relation, in combination with a new data analysis filter, to \emph{Swift} gamma-ray burst data, we demonstrate that it can constrain their rate density.

abs pdf

Jul 26, 2010

1007.4289 (/preprints)
2010-07-26, 23:07 [edit]


[1007.3973] Calibration of the LIGO Gravitational Wave Detectors in the Fifth Science Run

Authors: LIGO Scientific Collaboration

Date: 22 Jul 2010

Abstract: The Laser Interferometer Gravitational Wave Observatory (LIGO) is a network of three detectors built to detect local perturbations in the space-time metric from astrophysical sources. These detectors, two in Hanford, WA and one in Livingston, LA, are power-recycled Fabry-Perot Michelson interferometers. In their fifth science run (S5), between November 2005 and October 2007, these detectors accumulated one year of triple coincident data while operating at their designed sensitivity. In this paper, we describe the calibration of the instruments in the S5 data set, including measurement techniques and uncertainty estimation.

abs pdf

Jul 23, 2010

1007.3973 (/preprints)
2010-07-23, 01:10 [edit]


[1007.3545] Probing fundamental physics with pulsars

Authors: D.R. Lorimer, M.A. McLaughlin

Date: 21 Jul 2010

Abstract: Pulsars provide a wealth of information about General Relativity, the equation of state of superdense matter, relativistic particle acceleration in high magnetic fields, the Galaxy's interstellar medium and magnetic field, stellar and binary evolution, celestial mechanics, planetary physics and even cosmology. The wide variety of physical applications currently being investigated through studies of radio pulsars rely on: (i) finding interesting objects to study via large-scale and targeted surveys; (ii) high-precision timing measurements which exploit their remarkable clock-like stability. We review current surveys and the principles of pulsar timing and highlight progress made in the rotating radio transients, intermittent pulsars, tests of relativity, understanding pulsar evolution, measuring neutron star masses and the pulsar timing array.

abs pdf

Jul 22, 2010

1007.3545 (/preprints)
2010-07-22, 03:00 [edit]


[1007.2809] Critical Phenomena in Neutron Stars I: Linearly Unstable Nonrotating Models

Authors: David Radice, Luciano Rezzolla, Thorsten Kellermann

Date: 16 Jul 2010

Abstract: We consider the evolution in full general relativity of a family of linearly unstable isolated spherical neutron stars under the effects of very small, perturbations as induced by the truncation error. Using a simple ideal-fluid equation of state we find that this system exhibits a type-I critical behaviour, thus confirming the conclusions reached by Liebling et al. [1] for rotating magnetized stars. Exploiting the relative simplicity of our system, we are able carry out a more in-depth study providing solid evidences of the criticality of this phenomenon and also to give a simple interpretation of the putative critical solution as a spherical solution with the unstable mode being the fundamental F-mode. Hence for any choice of the polytropic constant, the critical solution will distinguish the set of subcritical models migrating to the stable branch of the models of equilibrium from the set of subcritical models collapsing to a black hole. Finally, we study how the dynamics changes when the numerically perturbation is replaced by a finite-size, resolution independent velocity perturbation and show that in such cases a nearly-critical solution can be changed into either a sub or supercritical. The work reported here also lays the basis for the analysis carried in a companion paper, where the critical behaviour in the the head-on collision of two neutron stars is instead considered [2].

abs pdf

Jul 19, 2010

1007.2809 (/preprints)
2010-07-19, 00:35 [edit]


[1007.2797] Critical Phenomena in Neutron Stars II: Head-on Collisions

Authors: Thorsten Kellermann, Luciano Rezzolla, David Radice

Date: 16 Jul 2010

Abstract: We consider the head-on collision of equal-mass neutron stars boosted towards each other and we study the behavior of such systems near the threshold of black-hole formation. In particular, we confirm the previous findings by [1] that a type-I critical phenomenon can be observed by fine-tuning the initial mass of the two neutron stars. At the same time, we argue against the interpretation that the critical solution is not a perturbed spherical star and show instead that the metastable star corresponds to a (perturbed) equilibrium solution on the unstable branch of the equilibrium configurations. As a result, the head-on collision of two neutron stars near the critical threshold can be seen as a transition in the space of configurations from an initial stable solution over to a critical metastable one which can either migrate to a stable solution or collapse to a black hole. The critical exponent for this process shows a fine structure which was already observed in the case of the critical collapse of scalar fields but never before for perfect fluids.

abs pdf

Jul 19, 2010

1007.2797 (/preprints)
2010-07-19, 00:35 [edit]


[1007.2662] Solving the Effective Field Equations for the Newtonian Potential

Authors: Sohyun Park, R. P. Woodard (University of Florida)

Date: 15 Jul 2010

Abstract: Loop corrections to the gravitational potential are usually inferred from scattering amplitudes, which seems quite different from how the linearized Einstein equations are solved with a static, point mass to give the classical potential. In this study we show how the Schwinger-Keldysh effective field equations can be used to compute loop corrections to the potential in a way which parallels the classical treatment. We derive explicit results for the one loop correction from the graviton self-energy induced by a massless, minimally coupled scalar.

abs pdf

Jul 19, 2010

1007.2662 (/preprints)
2010-07-19, 00:35 [edit]


[1007.2415] Neutron Star Radius Measurement with the Quiescent Low-Mass X-ray Binary U24 in NGC 6397

Authors: Sebastien Guillot, Robert E. Rutledge, Edward F. Brown

Date: 14 Jul 2010

Abstract: This paper reports the spectral and timing analyses of the quiescent low-mass X-ray binary U24 observed during five archived Chandra-ACIS exposures of the nearby globular cluster NGC 6397, for a total of 350 ksec. We find that the X-ray flux and the parameters of the hydrogen atmosphere spectral model are consistent with those previously published. Following the timing analysis, we find no evidence of short or long-term intensity variability. We also report the improved neutron star physical radius measurements, with statistical accuracy of the order of ~10%: R_ns = 8.9(+0.9)(-0.6) km for M_ns = 1.4 Msun. Alternatively, we provide the best-fit projected radius R_infinity= 11.9(+2.2)(-2.5)km, as seen by an observer at infinity. The best-fit effective temperature, kTeff = 80(+4)(-5) eV, is used to estimate the neutron star core temperature which falls in the range T_core = (3.0 - 9.8) x10 7 K, depending on the atmosphere model considered. This makes U24 the fourth most precisely measured neutron star radius among qLMXBs, after those in OmCen, in M13 and the qLMXB 47Tuc X7.

abs pdf

Jul 16, 2010

1007.2415 (/preprints)
2010-07-16, 00:09 [edit]


[1007.2614] High-Accuracy Comparison between the Post-Newtonian and Self-Force Dynamics of Black-Hole Binaries

Authors: Luc Blanchet, Steven Detweiler, Alexandre Le Tiec, Bernard F. Whiting

Date: 15 Jul 2010

Abstract: The relativistic motion of a compact binary system moving in circular orbit is investigated using the post-Newtonian (PN) approximation and the perturbative self-force (SF) formalism. A particular gauge-invariant observable quantity is computed as a function of the binary's orbital frequency. The conservative effect induced by the gravitational SF is obtained numerically with high precision, and compared to the PN prediction developed to high order. The PN calculation involves the computation of the 3PN regularized metric at the location of the particle. Its divergent self-field is regularized by means of dimensional regularization. The poles proportional to 1/(d-3) which occur within dimensional regularization at the 3PN order disappear from the final gauge-invariant result. The leading 4PN and next-to-leading 5PN conservative logarithmic contributions originating from gravitational-wave tails are also obtained. Making use of these exact PN results, some previously unknown PN coefficients are measured up to the very high 7PN order by fitting to the numerical self-force data. Using just the 2PN and new logarithmic terms, the value of the 3PN coefficient is also confirmed numerically with very high precision. The consistency of this cross-cultural comparison provides a crucial test of the very different regularization methods used in both SF and PN formalisms, and illustrates the complementarity of these approximation schemes when modelling compact binary systems.

abs pdf

Jul 16, 2010

1007.2614 (/preprints)
2010-07-16, 00:04 [edit]


[1007.2481] Spin and Clifford algebras, an introduction

Authors: Marc Lachieze-Rey (APC)

Date: 15 Jul 2010

Abstract: In this short pedagogical presentation, we introduce the spin groups and the spinors from the point of view of group theory. We also present, independently, the construction of the low dimensional Clifford algebras. And we establish the link between the two approaches. Finally, we give some notions of the generalisations to arbitrary spacetimes, by the introduction of the spin and spinor bundles.

abs pdf

Jul 16, 2010

1007.2481 (/preprints)
2010-07-16, 00:03 [edit]


[1007.2429] Linear Stability Analysis and the Speed of Gravitational Waves in Dynamical Chern-Simons Modified Gravity

Authors: David Garfinkle, Frans Pretorius, Nicolas Yunes

Date: 14 Jul 2010

Abstract: We perform a linear stability analysis of dynamical Chern-Simons modified gravity in the geometric optics approximation and find that it is linearly stable on the backgrounds considered. Our analysis also reveals that gravitational waves in the modified theory travel at the speed of light in Minkowski spacetime. However, on a Schwarzschild background the characteristic speed of propagation along a given direction splits into two modes, one subluminal and one superluminal. The width of the splitting depends on the azimuthal components of the propagation vector, is linearly proportional to the mass of the black hole, and decreases with the third inverse power of the distance from the black hole. Radial propagation is unaffected, implying that as probed by gravitational waves the location of the event horizon of the spacetime is unaltered. The analysis further reveals that when a high frequency, pure gravitational wave is scattered from a black hole, a scalar wave of comparable amplitude is excited, and vice-versa.

abs pdf

Jul 16, 2010

1007.2429 (/preprints)
2010-07-16, 00:02 [edit]


[1007.1995] Binary Pulsar Constraints on the Parameterized post-Einsteinian Framework

Authors: Nicolas Yunes, Scott A. Hughes

Date: 12 Jul 2010

Abstract: We constrain the parameterized post-Einsteinian framework with binary pulsar observations of orbital period decay due to gravitational wave emission. This framework proposes to enhance the amplitude and phase of gravitational waveform templates through post-Einsteinian parameters to search for generic deviations from General Relativity in gravitational wave data. Such enhancements interpolate between General Relativity and alternative theory predictions, but their magnitude must be such as to satisfy all current experiments and observations. The data that currently constrains the parameterized post-Einsteinian framework the most is the orbital period decay of binary pulsars. We use such observations to place upper limits on the magnitude of post-Einsteinian parameters, which will be critical when gravitational waves are detected and this framework is implemented.

abs pdf

Jul 15, 2010

1007.1995 (/preprints)
2010-07-15, 11:00 [edit]


[1007.2024] A hybrid method for understanding black-hole mergers: head-on case

Authors: David A. Nichols, Yanbei Chen

Date: 13 Jul 2010

Abstract: Black-hole-binary coalescence is often divided into three stages: inspiral, merger and ringdown. The post-Newtonian (PN) approximation treats the inspiral phase, black-hole perturbation (BHP) theory describes the ringdown, and the nonlinear dynamics of spacetime characterize the merger. In this paper, we introduce a hybrid method that incorporates elements of PN and BHP theories, and we apply it to the head-on collision of black holes with transverse, anti-parallel spins. We compare our approximation technique with a full numerical-relativity simulation, and we find good agreement between the gravitational waveforms and the radiated energy and momentum. Our results suggest that PN and BHP theories may suffice to explain the main features of outgoing gravitational radiation for head-on mergers. This would further imply that linear perturbations to exact black-hole solutions can capture the nonlinear aspects of head-on binary-black-hole mergers accessible to observers far from the collision.

abs pdf

Jul 15, 2010

1007.2024 (/preprints)
2010-07-15, 10:59 [edit]


[1007.1312] Spin induced multipole moments for the gravitational wave flux from binary inspirals to third Post-Newtonian order

Authors: Rafael A. Porto, Andreas Ross, Ira Z. Rothstein

Date: 8 Jul 2010

Abstract: Using effective field theory techniques we calculate the source multipole moments needed to obtain the spin contributions to the power radiated in gravitational waves from inspiralling compact binaries to third Post-Newtonian order (3PN). The multipoles depend linearly and quadratically on the spins and include both spin(1)spin(2) and spin(1)spin(1) components. The results in this paper provide the last missing ingredient required to determine the phase evolution to 3PN including all spin effects which we will report in a separate paper.

abs pdf

Jul 09, 2010

1007.1312 (/preprints)
2010-07-09, 21:47 [edit]


[1007.1218] Detection of gravitational waves from the QCD phase transition with pulsar timing arrays

Authors: Chiara Caprini, Ruth Durrer, Xavier Siemens

Date: 7 Jul 2010

Abstract: If the cosmological QCD phase transition is strongly first order and lasts sufficiently long, it generates a background of gravitational waves which may be detected via pulsar timing experiments. We estimate the amplitude and the spectral shape of such a background and we discuss its detectability prospects.

abs pdf

Jul 07, 2010

1007.1218 (/preprints)
2010-07-07, 18:03 [edit]


[1007.0425] Very Wide Binaries and Other Comoving Stellar Companions: A Bayesian Analysis of the Hipparcos Catalogue

Authors: Ed Shaya, Rob Olling

Date: 2 Jul 2010

Abstract: We develop Bayesian statistical methods for discovering and assigning probabilities to non-random (e.g., physical) stellar proper motion companions. They are either presently bound or from previously bound systems. The probabilities depend on similarities in proper motion parallel and perpendicular to the brighter component's motion, parallax, and the local phase-space density of field stars. Control experiments are conducted to understand the behavior of false positives. The technique is applied to the Hipparcos Catalogue within 100 pc. This is the first all-sky survey to locate escaped companions still drifting along with each other out to several parsecs. In both the 25 - 50 and the 50 - 100 pc distance ranges, about 50 high probability companions with separations between 0.01 - 1 pc are found. Evidence is found for a population of several 100 companions separated by 1 - 10 pc. We find these unnoticed naked-eye companions (both with V<6): {\delta} Vel and HIP43797, Alioth ({\epsilon} UMa) and Megrez ({\delta} UMa), {\gamma} and {\tau} Cen, {\phi} Eri and {\eta} Hor, 62 and 63 Cnc, {\gamma} and {\tau} Per, {\zeta} and {\delta} Hya, {\beta}02 and {\beta}03 Tuc, N Vel and HIP47479, {\iota} and 97 Tau, HIP98174 and HIP97646, {\nu} and 46 Tau, and 81 and 84 UMa. High probability fainter companions (V>6) of primaries with V<4 are found: Fomalhaut ({\alpha} PsA), Mizar, {\alpha} Lib, {\gamma} UMa, {\iota} Peg, {\alpha} Lib, {\delta} Boo, Alvahet ({\iota} Cephi), Chow ({\beta} Ser), {\delta} Ara, and {\kappa} Phe.

abs pdf

Jul 05, 2010

1007.0425 (/preprints)
2010-07-05, 09:13 [edit]


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