[0704.3764] Phenomenological template family for black-hole coalescence waveforms

Authors: P. Ajith, S. Babak, Y. Chen, M. Hewitson, B. Krishnan, J. T. Whelan, B. Bruegmann, P. Diener, J. Gonzalez, M. Hannam, S. Husa, M. Koppitz, D. Pollney, L. Rezzolla, L. Santamaria, A. M. Sintes, U. Sperhake, J. Thornburg

Date: 30 Apr 2007

Abstract: Recent progress in numerical relativity has enabled us to model the non-perturbative merger phase of the binary black-hole coalescence problem. Based on these results, we propose a phenomenological family of waveforms which can model the inspiral, merger, and ring-down stages of black hole coalescence. We also construct a template bank using this family of waveforms and discuss its implementation in the search for signatures of gravitational waves produced by black-hole coalescences in the data of ground-based interferometers. This template bank might enable us to extend the present inspiral searches to higher-mass binary black-hole systems, i.e., systems with total mass greater than about 80 solar masses, thereby increasing the reach of the current generation of ground-based detectors.

abs pdf

Apr 30, 2007

0704.3764 (/preprints)
2007-04-30, 18:00 [edit]


[0704.1968] Supermassive black hole binary mergers

Authors: Laszlo Gergely, Peter L. Biermann

Date: 16 Apr 2007

Abstract: Massive merging black holes will be the primary sources of powerful gravitational waves at low frequency, and will permit to test General Relativity if we identify candidate galaxies that are close to a binary black hole merger. In this paper we show that for a typical range of mass ratios of the two black holes the final stage of the merger is preceded by a rapid precession and a subsequent spin-flip of the main black hole. The latter already occurs in the inspiral phase, thus can be treated analytically by post-Newtonian techniques. We also show that the distance when gravitational radiation becomes the dominant dissipative effect (over dynamical friction) does not depend on this mass ratio. We then identify the radio galaxies with a super-disk as those in which the rapidly precessing jet produces effectively a powerful wind, which entrains the environmental gas to produce the appearance of a thick disk. These specific galaxies are thus candidates for a merger of two black holes to happen in the astronomically near future, and further observations and theoretical work may be capable of identifying which one is likely to be the next to merge, and how soon.

abs pdf

Apr 30, 2007

0704.1968 (/preprints)
2007-04-30, 13:45 [edit]


[astro-ph/0610076] Constraining population synthesis models via observations of compact-object binaries and supernovae

Authors: R. O'Shaughnessy (1), C. Kim (2)V. Kalogera (1), K. Belczynski (3) ((1) Northwestern University, (2) Cornell university, (3) New Mexico State University)

Date: 3 Oct 2006

Abstract: The observed samples of supernovae (SN) and double compact objects (DCOs) provide several critical constraints on population-synthesis models: the parameters of these models must be carefully chosen to reproduce, among other factors, (i) the formation rates of double neutron star (NS-NS) binaries and of white dwarf-neutron star (WD-NS) binaries, estimated from binary samples, and (ii) the type II and Ib/c supernova rates. Even allowing for extremely conservative accounting of the uncertainties in observational and theoretical predictions, we find only a few plausible population synthesis models
(roughly 9%) are consistent with DCO and SN rates empirically determined from observations. As a proof of concept, we describe the information that can be extracted about population synthesis models given such stringent observational tests, including surprisingly good agreement with the neutron star kick distributions inferred from pulsar proper-motion measurements. In the present study, we find that the current observational constraints favor: kicks described by a single Maxwellian with a typical velocity of about 300km/s; mass-loss fractions during non-conservative, but stable, mass transfer episodes of about 90%; and common envelope parameters of about 0.2-0.5. Finally, we use the subset of astrophysically consistent models to predict the rates at which black hole-neutron star (BH-NS) and NS-NS binaries merge in the Milky Way and the nearby Universe, assuming Milky-Way-like galaxies dominate. (Abridged)

abs pdf

Apr 30, 2007

0610076 (/preprints/astro-ph)
2007-04-30, 13:44 [edit]


[0704.3550] Final spin of a coalescing black-hole binary: an Effective-One-Body approach

Authors: Thibault Damour, Alessandro Nagar

Date: 26 Apr 2007

Abstract: We update the analytical estimate of the final spin of a coalescing black-hole binary derived within the Effective-One-Body (EOB) approach. We consider unequal-mass non-spinning black-hole binaries. It is found that a more complete account of relevant physical effects (higher post-Newtonian accuracy, ringdown losses) allows the {\it analytical} EOB estimate to ‘converge towards’ the recently obtained {\it numerical} results within 2%. This agreement illustrates the ability of the EOB approach to capture the essential physics of coalescing black-hole binaries. Our analytical approach allows one to estimate the final spin of the black hole formed by coalescing binaries in a mass range ($\nu=m_1m_2/(m_1+m_2)ˆ2 < 0.16 $) which is not presently covered by numerical simulations.

abs pdf

Apr 27, 2007

0704.3550 (/preprints)
2007-04-27, 08:54 [edit]


[0704.3338] Gravitomagnetism and its Measurements with Lunar Laser Ranging, LAGEOS Satellites and Gravity Probe B

Authors: Ignazio Ciufolini

Date: 25 Apr 2007

Abstract: We discuss here the measurement of gravitomagnetism and frame dragging with Lunar Laser Ranging, LAGEOS and LARES Satellites and Gravity Probe B.

abs pdf

Apr 25, 2007

0704.3338 (/preprints)
2007-04-25, 19:05 [edit]


[0704.3368] Search for gravitational waves from binary inspirals in S3 and S4 LIGO data

Authors: LIGO Scientific Collaboration: B. Abbott, et al

Date: 25 Apr 2007

Abstract: We report on a search for gravitational waves from the coalescence of compact binaries during the third and fourth LIGO science runs. The search focused on gravitational waves generated during the inspiral phase of the binary evolution. In our analysis, we considered three categories of compact binary systems, ordered by mass: (i) primordial black hole binaries with masses in the range 0.35 M(sun) < m1, m2 < 1.0 M(sun), (ii) binary neutron stars with masses in the range 1.0 M(sun) < m1, m2 < 3.0 M(sun), and (iii) binary black holes with masses in the range 3.0 M(sun)< m1, m2 < m_(max) with the additional constraint m1+ m2 < m_(max), where m_(max) was set to 40.0 M(sun) and 80.0 M(sun) in the third and fourth science runs, respectively. Although the detectors could probe to distances as far as tens of Mpc, no gravitational-wave signals were identified in the 1364 hours of data we analyzed. Assuming a binary population with a Gaussian distribution around 0.75-0.75 M(sun), 1.4-1.4 M(sun), and 5.0-5.0 M(sun), we derived 90%-confidence upper limit rates of 4.9 yrˆ(-1) L10ˆ(-1) for primordial black hole binaries, 1.2 yrˆ(-1) L10ˆ(-1) for binary neutron stars, and 0.5 yrˆ(-1) L10ˆ(-1) for stellar mass binary black holes, where L10 is 10ˆ(10) times the blue light luminosity of the Sun.

abs pdf

Apr 25, 2007

0704.3368 (/preprints)
2007-04-25, 19:05 [edit]


[0704.2983] Prospects for Stochastic Background Searches Using Virgo and LSC Interferometers

Authors: Giancarlo Cella, Carlo Nicola Colacino, Elena Cuoco, Angela Di Virgilio, Tania Regimbau, Emma L Robinson, John T Whelan (for the LSC-Virgo working group on stochastic backgrounds)

Date: 23 Apr 2007

Abstract: We consider the question of cross-correlation measurements using Virgo and the LSC Interferometers (LIGO Livingston, LIGO Hanford, and GEO600) to search for a stochastic gravitational-wave background. We find that inclusion of Virgo into the network will substantially improve the sensitivity to correlations above 200 Hz if all detectors are operating at their design sensitivity. This is illustrated using a simulated isotropic stochastic background signal, generated with an astrophysically-motivated spectrum, injected into 24 hours of simulated noise for the LIGO and Virgo interferometers.

abs pdf

Apr 23, 2007

0704.2983 (/preprints)
2007-04-23, 20:36 [edit]


[0704.2991] Second post-Newtonian approximation of scalar-tensor theory of gravity

Authors: Yi Xie, Wei-Tou Ni, Peng Dong, Tian-Yi Huang

Date: 23 Apr 2007

Abstract: Deep space laser ranging missions like ASTROD I (Single-Spacecraft Astrodynamical Space Test of Relativity using Optical Devices) and ASTROD, together with astrometry missions like GAIA and LATOR will be able to test relativistic gravity to an unprecedented level of accuracy. More precisely, these missions will enable us to test relativistic gravity to $10ˆ{-7}-10ˆ{-9}$, and will require 2nd post-Newtonian approximation of relevant theories of gravity. The first post-Newtonian approximation is valid to $10ˆ{-6}$ and the second post-Newtonian is valid to $10ˆ{-12}$ in the solar system. The scalar-tensor theory is widely discussed and used in tests of relativistic gravity, especially after the interests in inflation, cosmological constant and dark energy in cosmology. In the Lagrangian, intermediate-range gravity term has a similar form as cosmological term. Here we present the full second post-Newtonian approximation of the scalar-tensor theory including viable examples of intermediate-range gravity. We use Chandrasekhar's approach to derive the metric coefficients and the equation of the hydrodynamics governing a perfect fluid in the 2nd post-Newtonian approximation in scalar-tensor theory; all terms inclusive of $O(cˆ{-4})$ are retained consistently in the equation of motion.

abs pdf

Apr 23, 2007

0704.2991 (/preprints)
2007-04-23, 20:36 [edit]


[0704.2917] Extracting galactic binary signals from the first round of Mock LISA Data Challenges

Authors: Jeff Crowder, Neil J. Cornish

Date: 23 Apr 2007

Abstract: We report on the performance of an end-to-end Bayesian analysis pipeline for detecting and characterizing galactic binary signals in simulated LISA data. Our principal analysis tool is the Blocked-Annealed Metropolis Hasting (BAM) algorithm, which has been optimized to search for tens of thousands of overlapping signals across the LISA band. The BAM algorithm employs Bayesian model selection to determine the number of resolvable sources, and provides posterior distribution functions for all the model parameters. The BAM algorithm performed almost flawlessly on all the Round 1 Mock LISA Data Challenge data sets, including those with many highly overlapping sources. The only misses were later traced to a coding error that affected high frequency sources. In addition to the BAM algorithm we also successfully tested a Genetic Algorithm (GA), but only on data sets with isolated signals as the GA has yet to be optimized to handle large numbers of overlapping signals.

abs pdf

Apr 23, 2007

0704.2917 (/preprints)
2007-04-23, 20:35 [edit]


[0704.2881] Current status of Japanese detectors

Authors: Daisuke Tatsumi, Ryutaro Takahashi, Koji Arai, Noriyasu Nakagawa, Kazuhiro Agatsuma, Toshitaka Yamazaki, Mitsuhiro Fukushima, Masa-Katsu Fujimoto, Akiteru Takamori, Alessandro Bertolini, Virginio Sannibale, Riccardo DeSalvo, Szabolcs Marka, Masaki Ando, Kimio Tsubono, Tomomi Akutsu, Kazuhiro Yamamoto, Hideki Ishitsuka, Takashi Uchiyama, Shinji Miyoki, Masatake Ohashi, Kazuaki Kuroda, Norichika Awaya, Nobuyuki Kanda, Akito Araya, Souichi Telada, Takayuki Tomaru, Tomiyoshi Haruyama, Akira Yamamoto, Nobuaki Sato, Toshitaka Suzuki, Takakazu Shintomi

Date: 22 Apr 2007

Abstract: Current status of TAMA and CLIO detectors in Japan is reported in this article. These two interferometric gravitational-wave detectors are being developed for the large cryogenic gravitational wave telescope (LCGT) which is a future plan for detecting gravitational wave signals at least once per year.
TAMA300 is being upgraded to improve the sensitivity in low frequency region after the last observation experiment in 2004. To reduce the seismic noises, we are installing new seismic isolation system, which is called TAMA Seismic Attenuation System, for the four test masses. We confirmed stable mass locks of a cavity and improvements of length and angular fluctuations by using two SASs. We are currently optimizing the performance of the third and fourth SASs. We continue TAMA300 operation and R&D studies for LCGT. Next data taking in the summer of 2007 is planned.
CLIO is a 100-m baseline length prototype detector for LCGT to investigate interferometer performance in cryogenic condition. The key features of CLIO are that it locates Kamioka underground site for low seismic noise level, and adopts cryogenic Sapphire mirrors for low thermal noise level. The first operation of the cryogenic interferometer was successfully demonstrated in February of 2006. Current sensitivity at room temperature is close to the target sensitivity within a factor of 4. Several observation experiments at room temperature have been done. Once the displacement noise reaches at thermal noise level of room temperature, its improvement by cooling test mass mirrors should be demonstrated.

abs pdf

Apr 23, 2007

0704.2881 (/preprints)
2007-04-23, 20:35 [edit]


[0704.2720] Application of energy and angular momentum balance to gravitational radiation reaction for binary systems with spin-orbit coupling

Authors: Jing Zeng, Clifford M. Will (Washington University, St. Louis)

Date: 20 Apr 2007

Abstract: We study gravitational radiation reaction in the equations of motion for binary systems with spin-orbit coupling, at order (v/c)ˆ7 beyond Newtonian gravity, or O(v/c)ˆ2 beyond the leading radiation reaction effects for non-spinning bodies. We use expressions for the energy and angular momentum flux at infinity that include spin-orbit corrections, together with an assumption of energy and angular momentum balance, to derive equations of motion that are valid for general orbits and for a class of coordinate gauges. We show that the equations of motion are compatible with those derived earlier by a direct calculation.

abs pdf

Apr 23, 2007

0704.2720 (/preprints)
2007-04-23, 09:35 [edit]


[0704.2243] Post-Newtonian gravitational radiation and equations of motion via direct integration of the relaxed Einstein equations. V. The strong equivalence principle to second post-Newtonian order

Authors: Thomas Mitchell, Clifford M. Will (Washington University, St. Louis)

Date: 17 Apr 2007

Abstract: Using post-Newtonian equations of motion for fluid bodies valid to the second post-Newtonian order, we derive the equations of motion for binary systems with finite-sized, non-spinning but arbitrarily shaped bodies. In particular we study the contributions of the internal structure of the bodies (such as self-gravity) that would diverge if the size of the bodies were to shrink to zero. Using a set of virial relations accurate to the first post-Newtonian order that reflect the stationarity of each body, and redefining the masses to include 1PN and 2PN self-gravity terms, we show that a class of potentially divergent terms cancel, leaving 2PN equations of motion that depend only on the masses (modulo tidal effects). This is further evidence of the Strong Equivalence Principle, and supports the use of post-Newtonian approximations to derive equations of motion for strong-field bodies such as neutron stars and black holes. This extends earlier work done by Kopeikin.

abs pdf

Apr 19, 2007

0704.2243 (/preprints)
2007-04-19, 11:23 [edit]


[0704.1964] A data-analysis driven comparison of analytic and numerical coalescing binary waveforms: nonspinning case

Authors: Yi Pan, Alessandra Buonanno, John G. Baker, Joan Centrella, Bernard J. Kelly, Sean T. McWilliams, Frans Pretorius, James R. van Meter

Date: 16 Apr 2007

Abstract: We compare waveforms obtained by numerically evolving nonspinning binary black holes to post-Newtonian (PN) template families currently used in the search for gravitational waves by ground-based detectors. We find that the time-domain 3.5PN template family, which includes the inspiral phase, has fitting factors (FFs) >= 0.96 for binary systems with total mass M = 10 ~ 20 Msun. The time-domain 3.5PN effective-one-body template family, which includes the inspiral, merger and ring-down phases, gives satisfactory signal-matching performance with FFs >= 0.96 for binary systems with total mass M = 10 ~ 120 Msun. If we introduce a cutoff frequency properly adjusted to the final black-hole ring-down frequency, we find that the frequency-domain stationary-phase-approximated template family at 3.5PN order has FFs >= 0.96 for binary systems with total mass M = 10 ~ 20 Msun. However, to obtain high matching performances for larger binary masses, we need to either extend this family to unphysical regions of the parameter space or introduce a 4PN order coefficient in the frequency-domain GW phase. Finally, we find that the phenomenological Buonanno-Chen-Vallisneri family has FFs >= 0.97 with total mass M=10 ~ 120Msun. The main analyses use the noise spectral-density of LIGO, but several tests are extended to VIRGO and advanced LIGO noise-spectral densities.

abs pdf

Apr 16, 2007

0704.1964 (/preprints)
2007-04-16, 18:43 [edit]


[astro-ph/0703054] Alignment of the spins of supermassive black holes prior to coalescence

Authors: Tamara Bogdanovic, Christopher S. Reynolds, M. Coleman Miller (University of Maryland)

Date: 5 Mar 2007

Abstract: Recent numerical relativistic simulations of black hole coalescence suggest that in certain alignments the emission of gravitational radiation can produce a kick of several thousand kilometers per second. This exceeds galactic escape speeds, hence unless there a mechanism to prevent this, one would expect many galaxies that had merged to be without a central black hole. Here we show that in most galactic mergers, torques from accreting gas suffice to align the orbit and spins of both black holes with the large-scale gas flow. Such a configuration has a maximum kick speed <200 km/s, safely below galactic escape speeds. We predict, however, that in mergers of galaxies without much gas, the remnant will be kicked out several percent of the time. We also discuss other predictions of our scenario, including implications for jet alignment angles and X-type radio sources.

abs pdf

Apr 16, 2007

0703054 (/preprints/astro-ph)
2007-04-16, 08:42 [edit]


[0704.1808] Tests of Bayesian Model Selection Techniques for Gravitational Wave Astronomy

Authors: Neil J. Cornish, Tyson B. Littenberg

Date: 13 Apr 2007

Abstract: An important class of gravitational wave sources for the Laser Interferometer Space Antenna (LISA) are the millions of low-mass binary systems within our own galaxy, tens of thousands of which will be detectable. Because the number of resolvable galactic binaries is unknown, we are faced with a model selection problem. Not only are the number of sources unknown, but also the number of parameters required to model the waveforms. A significant subset of the resolvable galactic binaries will exhibit orbital frequency evolution, while a smaller number will have measurable eccentricity. In the Bayesian approach to model selection one needs to compute the Bayes factor for competing models. Here we explore various methods for computing Bayes factors in the context of determining which systems have measurable frequency evolution. The methods explored include a Reverse Jump Markov Chain Monte Carlo (RJMCMC) algorithm, Savage-Dickie density ratios, the Schwarz-Bayes Information Criteria (BIC), and the Laplace approximation to the model evidence. We find good agreement between all of the approaches.

abs pdf

Apr 16, 2007

0704.1808 (/preprints)
2007-04-16, 08:41 [edit]


[0704.1149] Contraction of Gravitational-Wave Packets Due to their Self-Gravity

Authors: Bence Kocsis, Abraham Loeb (Harvard)

Date: 10 Apr 2007

Abstract: When a source emits a gravity-wave (GW) pulse over a short period of time, the leading edge of the GW signal is moving outwards more slowly than the inner boundary of the pulse. The GW pulse is compressed by the gravitational effect of the self-energy residing in between these shells. We illustrate this compression for GW pulses from the final plunge of BH binaries, leading to the magnification and frequency blueshift of the GW signal. The compression depends on the total GW energy released and the duration of the emission, scaled by the total binary mass. The effect cannot be easily seen in finite box simulations because the GW shells approach each other only logarithmically with increasing distance from the source. For characteristic emission parameters at the final plunge between binary BHs of arbitrary spins, this effect could compress the simulated GW templates for LIGO and LISA by several percent over astrophysical distances. Measurement of the wave compression would allow to independently constrain distances and hence cosmological parameters, and will help to localize possible electromagnetic counterparts to GW sources.

abs pdf

Apr 12, 2007

0704.1149 (/preprints)
2007-04-12, 08:16 [edit]


[0704.1154] Information, information processing and gravity

Authors: Stephen D.H. Hsu

Date: 9 Apr 2007

Abstract: I discuss fundamental limits placed on information and information processing by gravity. Such limits arise because both information and its processing require energy, while gravitational collapse (formation of a horizon or black hole) restricts the amount of energy allowed in a finite region. Specifically, I use a criterion for gravitational collapse called the hoop conjecture. Once the hoop conjecture is assumed a number of results can be obtained directly: the existence of a fundamental uncertainty in spatial distance of order the Planck length, bounds on information (entropy) in a finite region, and a bound on the rate of information processing in a finite region. In the final section I discuss some cosmological issues related to the total amount of information in the universe, and note that almost all detailed aspects of the late universe are determined by the randomness of quantum outcomes. This paper is based on a talk presented at a 2007 Bellairs Research Institute (McGill University) workshop on black holes and quantum information.

abs pdf

Apr 12, 2007

0704.1154 (/preprints)
2007-04-12, 08:16 [edit]


[0704.1447] Can Gravity Probe B usefully constrain torsion gravity theories?

Authors: Eanna E. Flanagan, Eran Rosenthal

Date: 11 Apr 2007

Abstract: In most theories of gravity involving torsion, the source for torsion is the intrinsic spin of matter. Since the spins of fermions are normally randomly oriented in macroscopic bodies, the torsion generated is normally negligible. However, in a recent paper, Mao et al. point out that there is a class of theories in which the angular momentum of macroscopic spinning bodies generates a significant amount of torsion. They argue that by the principle of action equals reaction, one would expect the angular momentum of test bodies to couple to a background torsion field, and therefore the precession of the GPB gyroscopes should be affected in these theories by the torsion generated by the Earth. We show that in fact the principle of action equals reaction does not apply to these theories. We examine in detail a generalization of the Hayashi-Shirafuji theory suggested by Mao et al. called Einstein-Hayashi-Shirafuji theory. There are a variety of different versions of this theory, depending on the precise form of the coupling to matter chosen for the torsion. We show that for any coupling to matter that is compatible with the spin transport equation postulated by Mao et al., the theory has either ghosts, tachyons or an ill-posed initial value formulation. These theoretical problems can be avoided by specializing the parameters of the theory and in addition choosing the standard minimal coupling to matter of the torsion tensor. This yields a consistent theory, but one in which the action equals reaction principle is violated, and in which the angular momentum of the gyroscopes does not couple to the Earth's torsion field. Thus, the Einstein-Hayashi-Shirafuji theory does not predict a detectable torsion signal for Gravity Probe B. There may be other torsion theories which do.

abs pdf

Apr 12, 2007

0704.1447 (/preprints)
2007-04-12, 08:15 [edit]


[0704.1350] Specialized computer algebra system for application in general relativity

Authors: S. Tertychniy

Date: 11 Apr 2007

Abstract: A brief characteristic of the specialized computer algebra system GRG_EC intended for symbolic computations in the field of general relativity is given.

abs pdf

Apr 12, 2007

0704.1350 (/preprints)
2007-04-12, 08:15 [edit]


[0704.1086] Higher harmonics increase LISA's mass reach for supermassive black holes

Authors: K.G. Arun, Bala R. Iyer, B. S. Sathyaprakash, Siddhartha Sinha

Date: 9 Apr 2007

Abstract: Current expectations on the signal to noise ratios and masses of supermassive black holes which the Laser Interferometer Space Antenna (LISA) can observe are based on using in matched filtering only the dominant harmonic of the inspiral waveform at twice the orbital frequency. Other harmonics will affect the signal-to-noise ratio of systems currently believed to be observable by LISA. More significantly, inclusion of other harmonics in our matched filters would mean that more massive systems that were previously thought to be {\it not} visible in LISA should be detectable with reasonable SNRs. Our estimates show that we should be able to significantly increase the mass reach of LISA and observe the more commonly occurring supermassive black holes of masses $\sim 10ˆ8M_\odot.$ More specifically, with the inclusion of all known harmonics LISA will be able to observe even supermassive black hole coalescences with total mass $\sim 10ˆ8 M_\odot (10ˆ9M_\odot)$ (and mass-ratio 0.1) for a low frequency cut-off of $10ˆ{-4}{\rm Hz}$ $(10ˆ{-5}{\rm Hz})$ with an SNR up to $\sim 60$ $(\sim 30)$ at a distance of 3 Gpc. This is important from the astrophysical viewpoint since observational evidence for the existence of black holes in this mass range is quite strong and binaries containing such supermassive black holes will be inaccessible to LISA if one uses as detection templates only the dominant harmonic.

abs pdf

Apr 09, 2007

0704.1086 (/preprints)
2007-04-09, 17:42 [edit]


[0704.0799] Spin Evolution of Accreting Neutron Stars: Nonlinear Development of the R-mode Instability

Authors: Ruxandra Bondarescu, Saul A. Teukolsky, Ira Wasserman (Cornell University)

Date: 5 Apr 2007

Abstract: The nonlinear saturation of the r-mode instability and its effects on the spin evolution of Low Mass X-ray Binaries (LMXBs) are modeled using the triplet of modes at the lowest parametric instability threshold. We solve numerically the coupled equations for the three mode amplitudes in conjunction with the spin and temperature evolution equations. We observe that very quickly the mode amplitudes settle into quasi-stationary states. Once these states are reached, the mode amplitudes can be found algebraically and the system of equations is reduced from eight to two equations: spin and temperature evolution. Eventually, the system may reach thermal equilibrium and either (1) undergo a cyclic evolution with a frequency change of at most 10%, (2) evolve toward a full equilibrium state in which the accretion torque balances the gravitational radiation emission, or (3) enter a thermogravitational runaway on a very long timescale of about $10ˆ6$ years. Alternatively, a faster thermal runaway (timescale of about 100 years) may occur. The sources of damping considered are shear viscosity, hyperon bulk viscosity and boundary layer viscosity. We vary proprieties of the star such as the hyperon superfluid transition temperature $T_c$, the fraction of the star that is above the threshold for direct URCA reactions, and slippage factor, and map the different scenarios we obtain to ranges of these parameters. For all our bound evolutions the r-mode amplitude remains small $\sim 10ˆ{-5}$. The spin frequency is limited by boundary layer viscosity to $\nu_{max} \sim 800 Hz [S_{ns}/(M_{1.4} R_6)]ˆ{4/11} T_8ˆ{-2/11}$. We find that for $\nu > 700$ Hz the r-mode instability would be active for about 1 in 1000 LMXBs and that only the gravitational waves from LMXBs in the local group of galaxies could be detected by advanced LIGO interferometers.

abs pdf

Apr 09, 2007

0704.0799 (/preprints)
2007-04-09, 17:42 [edit]


[0704.0943] Search for gravitational-wave bursts in LIGO data from the fourth science run

Authors: LIGO Scientific Collaboration

Date: 6 Apr 2007

Abstract: The fourth science run of the LIGO and GEO 600 gravitational-wave detectors, carried out in early 2005, collected data with significantly lower noise than previous science runs. We report on a search for short-duration gravitational-wave bursts with arbitrary waveform in the 64-1600 Hz frequency range appearing in all three LIGO interferometers. Signal consistency tests, data quality cuts, and auxiliary-channel vetoes are applied to reduce the rate of spurious triggers. No gravitational-wave signals are detected in 15.5 days of live observation time; we set a frequentist upper limit of 0.15 per day (at 90% confidence level) on the rate of bursts with large enough amplitudes to be detected reliably. The amplitude sensitivity of the search, characterized using Monte Carlo simulations, is several times better than that of previous searches. We also provide rough estimates of the distances at which representative supernova and binary black hole merger signals could be detected with 50% efficiency by this analysis.

abs pdf

Apr 09, 2007

0704.0943 (/preprints)
2007-04-09, 17:38 [edit]


[0704.0754] General Relativity Today

Authors: Thibault Damour

Date: 5 Apr 2007

Abstract: After recalling the conceptual foundations and the basic structure of general relativity, we review some of its main modern developments (apart from cosmology) : (i) the post-Newtonian limit and weak-field tests in the solar system, (ii) strong gravitational fields and black holes, (iii) strong-field and radiative tests in binary pulsar observations, (iv) gravitational waves, (v) general relativity and quantum theory.

abs pdf

Apr 05, 2007

0704.0754 (/preprints)
2007-04-05, 17:47 [edit]


[0704.0749] Binary Systems as Test-beds of Gravity Theories

Authors: Thibault Damour

Date: 5 Apr 2007

Abstract: We review the general relativistic theory of the motion, and of the timing, of binary systems containing compact objects (neutron stars or black holes). Then we indicate the various ways one can use binary pulsar data to test the strong-field and/or radiative aspects of General Relativity, and of general classes of alternative theories of relativistic gravity.

abs pdf

Apr 05, 2007

0704.0749 (/preprints)
2007-04-05, 17:47 [edit]


[0704.0719] Gravitational Wave Signals from Chaotic System: A Point Mass with A Disk

Authors: Kenta Kiuchi, Hiroko Koyama, Kei-ichi Maeda

Date: 5 Apr 2007

Abstract: We study gravitational waves from a particle moving around a system of a point mass with a disk in Newtonian gravitational theory. A particle motion in this system can be chaotic when the gravitational contribution from a surface density of a disk is comparable with that from a point mass. In such an orbit, we sometimes find that there appears a phase of the orbit in which particle motion becomes to be nearly regular (the so-called ‘stagnant motion’) for a finite time interval between more strongly chaotic phases. To study how these different chaotic behaviours affect on observation of gravitational waves, we investigate a correlation of the particle motion and the waves. We find that such a difference in chaotic motions reflects on the wave forms and energy spectra. The character of the waves in the stagnant motion is quite different from that either in a regular motion or in a more strongly chaotic motion. This suggests that we may make a distinction between different chaotic behaviours of the orbit via the gravitational waves.

abs pdf

Apr 05, 2007

0704.0719 (/preprints)
2007-04-05, 17:46 [edit]


[gr-qc/0701170] An overview of the second round of the Mock LISA Data Challenges

Authors: K A Arnaud, S Babak, J Baker, M J Benacquista, N J Cornish, C Cutler, L S Finn, S L Larson, T Littenberg, E K Porter, B S Sathyaprakash, M Vallisneri, A Vecchio, J-Y Vinet (the Mock LISA Data Challenge Task Force)

Date: 30 Jan 2007

Abstract: The Mock Data Challenges (MLDCs) have the dual purpose of fostering the development of LISA data-analysis tools and capabilities and of demonstrating the technical readiness already achieved by the gravitational-wave community in distilling a rich science payoff from the LISA data. The first round of MLDCs has just been completed and the second-round data sets are being released shortly after this workshop. The second-round data sets contain radiation from an entire Galactic population of stellar-mass binary systems, from massive--black-hole binaries, and from extreme--mass-ratio inspirals. These data sets are designed to capture much of the complexity that is expected in the actual LISA data, and should provide a fairly realistic setting to test advanced data-analysis techniques, and in particular the global aspect of the analysis. Here we describe the second round of MLDCs and provide details about its implementation.

abs pdf

Apr 04, 2007

0701170 (/preprints/gr-qc)
2007-04-04, 22:43 [edit]


[0704.0299] Parametrized Post-Newtonian Expansion of Chern-Simons Gravity

Authors: Stephon Alexander, Nicolas Yunes

Date: 3 Apr 2007

Abstract: We investigate the weak-field, post-Newtonian expansion to the solution of the field equations in Chern-Simons gravity with a perfect fluid source. In particular, we study the mapping of this solution to the parameterized post-Newtonian formalism to 1 PN order in the metric. We find that the PPN parameters of Chern-Simons gravity are identical to those of general relativity, with the exception of the inclusion of a new term that is proportional to the Chern-Simons coupling parameter and the curl of the PPN vector potentials. We also find that the new term is naturally enhanced by the non-linearity of spacetime and we provide a physical interpretation for it. By mapping this correction to the gravito-electro-magnetic framework, we study the corrections that this new term introduces to the acceleration of point particles and the frame-dragging effect in gyroscopic precession. We find that the Chern-Simons correction to these classical predictions could be used by current and future experiments to place bounds on intrinsic parameters of Chern-Simons gravity and, thus, string theory.

abs pdf

Apr 04, 2007

0704.0299 (/preprints)
2007-04-04, 22:42 [edit]


[0704.0138] Circular and non-circular nearly horizon-skimming orbits in Kerr spacetimes

Authors: Enrico Barausse, Scott A. Hughes, Luciano Rezzolla

Date: 2 Apr 2007

Abstract: We have performed a detailed analysis of orbital motion in the vicinity of a nearly extremal Kerr black hole. For very rapidly rotating black holes -- spin parameter a = J/M > 0.9524M -- we have found a class of very strong field eccentric orbits whose orbital angular momentum L_z increases with the orbit's inclination with respect to the equatorial plane, while keeping latus rectum and eccentricity fixed. This behavior is in contrast with Newtonian intuition, and is in fact opposite to the ‘normal’ behavior of black hole orbits. Such behavior was noted previously for circular orbits; since it only applies to orbits very close to the black hole, they were named ‘nearly horizon-skimming orbits’. Our current analysis generalizes this result, mapping out the full generic (inclined and eccentric) family of nearly horizon-skimming orbits. The earlier work on circular orbits reported that, under gravitational radiation emission, nearly horizon-skimming orbits exhibit unusual inspiral, tending to evolve to smaller orbit inclination, toward prograde equatorial configuration. Normal orbits, by contrast, always demonstrate slowly {\it growing} orbit inclination -- orbits evolve toward the retrograde equatorial configuration. Using up-to-date Teukolsky-based fluxes, we have concluded that the earlier result was incorrect -- all orbits, {\it including nearly horizon skimming ones}, exhibit growing orbit inclination under radiative backreaction. We also find that the inclination change is, in any case, very small. As such, we conclude that these orbits are {\it not} not likely to have a clear and peculiar imprint on the gravitational waveforms expected to be measured by the space-based detector LISA.

abs pdf

Apr 02, 2007

0704.0138 (/preprints)
2007-04-02, 23:13 [edit]


[0704.0048] Inference on white dwarf binary systems using the first round Mock LISA Data Challenges data sets

Authors: Alexander Stroeer, John Veitch, Christian Roever, Ed Bloomer, James Clark, Nelson Christensen, Martin Hendry, Chris Messenger, Renate Meyer, Matthew Pitkin, Jennifer Toher, Richard Umstaetter, Alberto Vecchio, Graham Woan

Date: 31 Mar 2007

Abstract: We report on the analysis of selected single source data sets from the first round of the Mock LISA Data Challenges (MLDC) for white dwarf binaries. We implemented an end-to-end pipeline consisting of a grid-based coherent pre-processing unit for signal detection, and an automatic Markov Chain Monte Carlo post-processing unit for signal evaluation. We demonstrate that signal detection with our coherent approach is secure and accurate, and is increased in accuracy and supplemented with additional information on the signal parameters by our Markov Chain Monte Carlo approach. We also demonstrate that the Markov Chain Monte Carlo routine is additionally able to determine accurately the noise level in the frequency window of interest.

abs pdf

Apr 02, 2007

0704.0048 (/preprints)
2007-04-02, 23:12 [edit]


[gr-qc/0703155] A fast search strategy for gravitational waves from low-mass X-ray binaries

Authors: C. Messenger, G. Woan

Date: 30 Mar 2007

Abstract: We present a new type of search strategy designed specifically to find continuously emitting gravitational wave sources in known binary systems based on the incoherent sum of frequency modulated binary signal sidebands. The search pipeline can be divided into three stages: the first is a wide bandwidth, F-statistic search demodulated for sky position. This is followed by a fast second stage in which areas in frequency space are identified as signal candidates through the frequency domain convolution of the F-statistic with an approximate signal template. For this second stage only precise information on the orbit period and approximate information on the orbital semi-major axis are required apriori. For the final stage we propose a fully coherent Markov chain monte carlo based follow up search on the frequency subspace defined by the candidates identified by the second stage. This search is particularly suited to the low-mass X-ray binaries, for which orbital period and sky position are typically well known and additional orbital parameters and neutron star spin frequency are not. We note that for the accreting X-ray millisecond pulsars, for which spin frequency and orbital parameters are well known, the second stage can be omitted and the fully coherent search stage can be performed. We describe the search pipeline with respect to its application to a simplified phase model and derive the corresponding sensitivity of the search.

abs pdf

Apr 02, 2007

0703155 (/preprints/gr-qc)
2007-04-02, 23:10 [edit]


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