## [0706.4286] Measuring eccentricity in binary black-hole initial data

Authors: Jason D. Grigsby, Gregory B. Cook

Date: 28 Jun 2007

Abstract: Initial data for evolving black-hole binaries can be constructed via many techniques, and can represent a wide range of physical scenarios. However, because of the way that different schemes parameterize the physical aspects of a configuration, it is not alway clear what a given set of initial data actually represents. This is especially important for quasiequilibrium data constructed using the conformal thin-sandwich approach. Most initial-data studies have focused on identifying data sets that represent binaries in quasi-circular orbits. In this paper, we consider initial-data sets representing equal-mass black holes binaries in eccentric orbits. We will show that effective-potential techniques can be used to calibrate initial data for black-hole binaries in eccentric orbits. We will also examine several different approaches, including post-Newtonian diagnostics, for measuring the eccentricity of an orbit. Finally, we propose the use of the ‘Komar-mass difference’ as a useful, invariant means of parameterizing the eccentricity of relativistic orbits.

#### Jun 29, 2007

0706.4286 (/preprints)
2007-06-29, 09:30 

## [gr-qc/0703152] Binary system delays and timing noise in searches for gravitational waves from known pulsars

Authors: Matthew Pitkin, Graham Woan (University of Glasgow)

Date: 30 Mar 2007

Abstract: The majority of fast millisecond pulsars are in binary systems, so that any periodic signal they emit is modulated by both Doppler and relativistic effects. Here we show how well-established binary models can be used to account for these effects in searches for gravitational waves from known pulsars within binary systems. A seperate issue affecting certain pulsar signals is that of timing noise and we show how this, with particular reference to the Crab pulsar, can be compensated for by using regularly updated timing ephemerides.

#### Jun 27, 2007

0703152 (/preprints/gr-qc)
2007-06-27, 23:01 

## [gr-qc/0702039] Upper limits on gravitational wave emission from 78 radio pulsars

Authors: The LIGO Scientific Collaboration: B. Abbott, et al, M. Kramer, A. G. Lyne

Date: 7 Feb 2007

Abstract: We present upper limits on the gravitational wave emission from 78 radio pulsars based on data from the third and fourth science runs of the LIGO and GEO600 gravitational wave detectors. The data from both runs have been combined coherently to maximise sensitivity. For the first time pulsars within binary (or multiple) systems have been included in the search by taking into account the signal modulation due to their orbits. Our upper limits are therefore the first measured for 56 of these pulsars. For the remaining 22, our results improve on previous upper limits by up to a factor of 10. For example, our tightest upper limit on the gravitational strain is 2.6e-25 for PSRJ1603-7202, and the equatorial ellipticity of PSRJ2124-3358 is less than 10ˆ{-6}. Furthermore, our strain upper limit for the Crab pulsar is only 2.2 times greater than the fiducial spin-down limit.

#### Jun 27, 2007

0702039 (/preprints/gr-qc)
2007-06-27, 23:01 

## [0706.3732] Toward faithful templates for non-spinning binary black holes using the effective-one-body approach

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

Date: 25 Jun 2007

Abstract: We present an accurate approximation of the full gravitational radiation waveforms generated in the merger of non-eccentric systems of two non-spinning black holes. Utilizing information from recent numerical relativity simulations and the natural flexibility of the effective-one-body (EOB) model, we extend the latter so that it can successfully match the numerical relativity waveforms during the last stages of inspiral, merger and ringdown. By ‘successfully’ here, we mean with phase differences < 8% of a gravitational-wave cycle accumulated by the end of the ringdown phase, maximizing only over time of arrival and initial phase. We obtain this result by simply adding a 4-post-Newtonian order correction in the EOB radial potential and determining the (constant) coefficient by imposing high-matching performances with numerical waveforms of mass ratios m1/m2 = 1, 3/2, 2 and 4, m1 and m2 being the individual black-hole masses. The final black-hole mass and spin predicted by the numerical simulations are used to determine the ringdown frequency and decay time of three quasi-normal-mode damped sinusoids that are attached to the EOB inspiral-(plunge) waveform at the EOB light-ring. The EOB waveforms might be tested and further improved in the future by comparison with extremely long and accurate inspiral numerical-relativity waveforms. They may be already employed for coherent searches and parameter estimation of gravitational waves emitted by non-spinning coalescing binary black holes with ground-based laser-interferometer detectors.

#### Jun 27, 2007

0706.3732 (/preprints)
2007-06-27, 08:16 

## [0705.3481] Gravitational waveforms for finite mass binaries

Authors: M&#xe1;ty&#xe1;s Vas&#xfa;th, J&#xe1;nos Maj&#xe1;r

Date: 23 May 2007

Abstract: One of the promising sources of gravitational radiation is a binary system composed of compact stars. It is an important question how the rotation of the bodies and the eccentricity of the orbit affect the detectable signal. Here we present a method to evaluate the gravitational wave polarization states for inspiralling compact binaries with comparable mass. We consider eccentric orbits and the spin-orbit contribution in the case of one spinning object up to 1.5 post-Newtonian order. For circular orbits our results are in agreement with existing calculations.

#### Jun 20, 2007

0705.3481 (/preprints)
2007-06-20, 21:35 

## [0706.2541] Binary Black Holes: Spin Dynamics and Gravitational Recoil

Authors: Frank Herrmann, Ian Hinder, Deirdre M. Shoemaker, Pablo Laguna, Richard A. Matzner

Date: 18 Jun 2007

Abstract: We present a study of spinning black hole binaries focusing on the spin dynamics of the individual black holes as well as on the gravitational recoil acquired by the black hole produced by the merger. We consider two series of initial spin orientations away from the binary orbital plane. In one of the series, the spins are anti-aligned; for the second series, one of the spins points away from the binary along the line separating the black holes. We find a remarkable agreement between the spin dynamics predicted at 2nd post-Newtonian order and those from numerical relativity. For each configuration, we compute the kick of the final black hole. We use the kick estimates from the series with anti-aligned spins to fit the parameters in the Kidder kick formula, and verify that the recoil along the direction of the orbital angular momentum is proportional to $\sin\theta$ and on the orbital plane to $\cos\theta$, with $\theta$ the angle between the spin directions and the orbital angular momentum.

#### Jun 18, 2007

0706.2541 (/preprints)
2007-06-18, 18:21 

## [0706.2412] Generalized gauge-invariance for gravitational waves

Authors: Christian Corda

Date: 16 Jun 2007

Abstract: The gauge-invariance of the response of interferometers to gravitational waves (GWs) between the Tranverse-Traceless (TT) gauge, where, in general, computations on GWs are performed, and the gauge of the local observer, which is the gauge of a laboratory environment on Earth, is shown in its full angular and frequency dependences, while in previous works in the literature this gauge-invariance was shown only in the low frequencies approximation or in the simplest geometry of the interferometers. In the computation of the response functions in the gauge of the local observer, a common misconception about interferometers is also clarifed.

#### Jun 18, 2007

0706.2412 (/preprints)
2007-06-18, 18:21 

## [0706.1305] Where post-Newtonian and numerical-relativity waveforms meet

Authors: Mark Hannam, Sascha Husa, Ulrich Sperhake, Bernd Bruegmann, Jose A. Gonzalez

Date: 11 Jun 2007

Abstract: We analyze numerical waveforms that cover 18 cycles before merger of an equal-mass system with low eccentricity, with uncertainties of less than 0.3% in the phase and less than 1% in the amplitude; such accuracy allows a direct comparison with post-Newtonian (PN) waveforms. We focus on the restricted 3.5PN Taylor waveforms used by data analysts, and find that the wave amplitude disagrees with numerical results by about 7%, but that the accumulated phase disagreement is no more than 0.15 radians over 13 cycles. The amplitude disagreement is roughly constant for all 18 cycles, and we conclude that only the last 4.5 orbits need to be simulated numerically in order to match with restricted 3.5PN waveforms. If however we model the amplitude up to 2.5PN order, the amplitude disagreement is roughly within numerical error up to about 11 cycles before merger.

#### Jun 12, 2007

0706.1305 (/preprints)
2007-06-12, 08:30 

## [0706.1513] How to tell a gravastar from a black hole

Authors: Cecilia B. M. H. Chirenti, Luciano Rezzolla

Date: 11 Jun 2007

Abstract: Gravastars have been recently proposed as potential alternatives to explain the astrophysical phenomenology traditionally associated to black holes, raising the question of whether the two objects can be distinguished at all. Leaving aside the debate about the processes that would lead to the formation of a gravastar and the astronomical evidence in their support, we here address two basic questions: Is a gravastar stable against generic perturbations? If stable, can an observer distinguish it from a black hole of the same mass? To answer these questions we construct a general class of gravastars and determine the conditions they must satisfy in order to exist as equilibrium solutions of the Einstein equations. For such models we perform a systematic stability analysis against axial-perturbations, computing the real and imaginary parts of the eigenfrequencies. Overall, we find that gravastars are stable to axial perturbations, but also that their quasi-normal modes differ from those of a black hole of the same mass and thus can be used to discern, beyond dispute, a gravastar from a black hole.

#### Jun 12, 2007

0706.1513 (/preprints)
2007-06-12, 08:30 

## [0706.1109] Discovering the Kerr and Kerr-Schild metrics

Authors: Roy P. Kerr

Date: 8 Jun 2007

Abstract: An historical account of the reasoning that led to the discovery of the Kerr and Kerr-Schild metrics in 1963-1964, and their physical interpretation as rotating black holes, is presented.

#### Jun 10, 2007

0706.1109 (/preprints)
2007-06-10, 19:06 

## [0706.0288] Bumpy black holes from spontaneous Lorentz violation

Authors: Sergei Dubovsky, Peter Tinyakov, Matias Zaldarriaga

Date: 2 Jun 2007

Abstract: We consider black holes in Lorentz violating theories of massive gravity. We argue that in these theories black hole solutions are no longer universal and exhibit a large number of hairs. If they exist, these hairs probe the singularity inside the black hole providing a window into quantum gravity. The existence of these hairs can be tested by future gravitational wave observatories. We generically expect that the effects we discuss will be larger for the more massive black holes. In the simplest models the strength of the hairs is controlled by the same parameter that sets the mass of the graviton (tensor modes). Then the upper limit on this mass coming from the inferred gravitational radiation emitted by binary pulsars implies that hairs are likely to be suppressed for almost the entire mass range of the super-massive black holes in the centers of galaxies.

#### Jun 06, 2007

0706.0288 (/preprints)
2007-06-06, 20:19 

## [0706.0740] Reducing phase error in long numerical binary black hole evolutions with sixth order finite differencing

Authors: Sascha Husa, Jose A. Gonzalez, Mark Hannam, Bernd Bruegmann, Ulrich Sperhake

Date: 5 Jun 2007

Abstract: We describe a modification of a fourth-order accurate ‘moving puncture’ evolution code, where by replacing spatial fourth-order accurate differencing operators in the bulk of the grid by a specific choice of sixth-order accurate stencils we gain significant improvements in accuracy. We illustrate the performance of the modified algorithm with an equal-mass simulation covering nine orbits.

#### Jun 06, 2007

0706.0740 (/preprints)
2007-06-06, 20:11 

## [0706.0622] The Kerr spacetime: A brief introduction

Authors: Matt Visser (Victoria University of Wellington)

Date: 5 Jun 2007

Abstract: This chapter provides a brief introduction to the Kerr spacetime and rotating black holes, touching on the most common coordinate representations of the spacetime metric and the key features of the geometry -- the presence of horizons and ergospheres. The coverage is by no means complete, and serves chiefly to orient oneself when reading subsequent chapters.

#### Jun 05, 2007

0706.0622 (/preprints)
2007-06-05, 20:03 

## [0706.0726] Radiation reaction in the 2.5PN waveform from inspiralling binaries in circular orbits

Authors: Lawrence E. Kidder, Luc Blanchet, Bala R. Iyer

Date: 5 Jun 2007

Abstract: In this Comment we compute the contributions of the radiation reaction force in the 2.5 post-Newtonian (PN) gravitational wave polarizations for compact binaries in circular orbits. (i) We point out and correct an inconsistency in the derivation of Arun, Blanchet, Iyer, and Qusailah. (ii) We prove that all contributions from radiation reaction in the 2.5PN waveform are actually negligible since they can be absorbed into a modification of the orbital phase at the 5PN order.

#### Jun 05, 2007

0706.0726 (/preprints)
2007-06-05, 20:03 

## [0706.0114] A New Template Family For The Detection Of Gravitational Waves From Comparable Mass Black Hole Binaries

Authors: Edward K. Porter

Date: 1 Jun 2007

Abstract: In order to improve the phasing of the comparable-mass waveform as we approach the last stable orbit for a system, various re-summation methods have been used to improve the standard post-Newtonian waveforms. In this work we present a new family of templates for the detection of gravitational waves from the inspiral of two comparable-mass black hole binaries. These new adiabatic templates are based on re-expressing the derivative of the binding energy and the gravitational wave flux functions in terms of shifted Chebyshev polynomials. The Chebyshev polynomials are a useful tool in numerical methods as they display the fastest convergence of any of the orthogonal polynomials. In this case they are also particularly useful as they eliminate one of the features that plagues the post-Newtonian expansion : The Chebyshev binding energy now has information at all post-Newtonian orders, compared to the post-Newtonian templates which only have integer at full integer orders. In this work, we compare both the post-Newtonian and Chebyshev templates against a fiducially exact waveform. This waveform is constructed from a hybrid method of using the test-mass results combined with the mass dependent parts of the post-Newtonian expansions for the binding energy and flux functions. Our results show that the Chebyshev templates achieve extremely high fitting factors at all PN orders and have excellent parameter extraction. We also show that this new template family has a faster Cauchy convergence, gives a better prediction of the position of the Last Stable Orbit and in general recovers higher Signal-to-Noise ratios than the post-Newtonian templates.

#### Jun 03, 2007

0706.0114 (/preprints)
2007-06-03, 19:04