## [0908.3889] Integrating Post-Newtonian Equations on Graphics Processing Units

Authors: Frank Herrmann, John Silberholz, Matias Bellone, Gustavo Guerberoff, Manuel Tiglio

Date: 26 Aug 2009

Abstract: We report on early results of a numerical and statistical study of binary black hole inspirals. The two black holes are evolved using post-Newtonian approximations starting with initially randomly distributed spin vectors. We characterize certain aspects of the distribution shortly before merger. In particular we note the uniform distribution of black hole spin vector dot products shortly before merger and a high correlation between the initial and final black hole spin vector dot products in the equal-mass, maximally spinning case. These simulations were performed on Graphics Processing Units, and we demonstrate a speed-up of a factor 50 over a more conventional CPU implementation.

#### Aug 30, 2009

0908.3889 (/preprints)
2009-08-30, 12:41 

## [0908.3854] Third post-Newtonian angular momentum flux and the secular evolution of orbital elements for inspiralling compact binaries in quasi-elliptical orbits

Authors: K. G. Arun, Luc Blanchet, Bala R. Iyer, Siddhartha Sinha

Date: 26 Aug 2009

Abstract: The angular momentum flux from an inspiralling binary system of compact objects moving in quasi-elliptical orbits is computed at the third post-Newtonian (3PN) order using the multipolar post-Minkowskian wave generation formalism. The 3PN angular momentum flux involves the instantaneous, tail, and tail-of-tails contributions as for the 3PN energy flux, and in addition a contribution due to non-linear memory. We average the angular momentum flux over the binary's orbit using the 3PN quasi-Keplerian representation of elliptical orbits. The averaged angular momentum flux provides the final input needed for gravitational wave phasing of binaries moving in quasi-elliptical orbits. We obtain the evolution of orbital elements under 3PN gravitational radiation reaction in the quasi-elliptic case. For small eccentricities, we give simpler limiting expressions relevant for phasing up to order $eˆ2$. This work is important for the construction of templates for quasi-eccentric binaries, and for the comparison of post-Newtonian results with the numerical relativity simulations of the plunge and merger of eccentric binaries.

#### Aug 30, 2009

0908.3854 (/preprints)
2009-08-30, 12:41 

## [0908.4006] Current status of gravitational-wave observations

Authors: Stephen Fairhurst, Gianluca M Guidi, Patrice Hello, John T Whelan, Graham Woan

Date: 27 Aug 2009

Abstract: The first generation of gravitational wave interferometric detectors has taken data at, or close to, their design sensitivity. This data has been searched for a broad range of gravitational wave signatures. An overview of gravitational wave search methods and results are presented. Searches for gravitational waves from unmodelled burst sources, compact binary coalescences, continuous wave sources and stochastic backgrounds are discussed.

#### Aug 30, 2009

0908.4006 (/preprints)
2009-08-30, 12:41 

## [0908.3766] Searching for Galactic White Dwarf Binaries in the Second Mock LISA Data Challenge using an F-Statistic Template Bank

Authors: John T. Whelan, Reinhard Prix, Deepak Khurana

Date: 26 Aug 2009

Abstract: We describe the application of an F-statistic search for continuous gravitational waves to the search for galactic white-dwarf binaries in the Second Mock LISA Data Challenge. The search method employs a hierarchical template-grid based exploration of the parameter space, using a coincidence step to distinguish between primary ("true") and secondary maxima, followed by a final (multi-TDI) "zoom" stage to provide an accurate parameter estimation of the final candidates. Suitably tuned, the pipeline is able to extract 1989 true signals with only 5 false alarms. The use of the rigid adiabatic approximation allows recovery of signal parameters comparable to statistical expectations, although there is still some systematic excess above expected statistical errors due to Gaussian noise. An experimental iterative pipeline with seven rounds of subtraction and re-analysis allows us to increase the number of signals recovered, up to a total of 3419 with 29 false alarms.

#### Aug 30, 2009

0908.3766 (/preprints)
2009-08-30, 12:41 

## [0908.3665] X-Pipeline: An analysis package for autonomous gravitational-wave burst searches

Authors: Patrick J. Sutton, Gareth Jones, Shourov Chatterji, Peter Michael Kalmus, Isabel Leonor, Stephen Poprocki, Jameson Rollins, Antony Searle, Leo Stein, Massimo Tinto, Michal Was

Date: 25 Aug 2009

Abstract: Autonomous gravitational-wave searches -- fully automated analyses of data that run without human intervention or assistance -- are desirable for a number of reasons. They are necessary for the rapid identification of gravitational-wave burst candidates, which in turn will allow for follow-up observations by other observatories and the maximum exploitation of their scientific potential. A fully automated analysis would also circumvent the traditional "by hand" setup and tuning of burst searches that is both labourious and time consuming. We demonstrate a fully automated search with X-Pipeline, a software package for the coherent analysis of data from networks of interferometers for detecting bursts associated with GRBs and other astrophysical triggers. We discuss the methods X-Pipeline uses for automated running, including background estimation, efficiency studies, unbiased optimal tuning of search thresholds, and prediction of upper limits. These are all done automatically via Monte Carlo with multiple independent data samples, and without requiring human intervention. As a demonstration of the power of this approach, we apply X-Pipeline to LIGO data to search for gravitational-wave emission associated with GRB 031108. We find that X-Pipeline is sensitive to signals approximately a factor of 2 weaker in amplitude than those detectable by the cross-correlation technique used in LIGO searches to date. We conclude with the prospects for running X-Pipeline as a fully autonomous, near real-time triggered burst search in the next LSC-Virgo Science Run.

#### Aug 26, 2009

0908.3665 (/preprints)
2009-08-26, 09:17 

## [0908.2043] Shapiro delay of asteroids on LISA

Authors: Bertrand Chauvineau (1), Sophie Pireaux (1,2), Tania Regimbau (1), ((1) Observatoire de la Cote d&#x27;Azur, France; (2) Observatoire Royal de Belgique, Belgium)

Date: 14 Aug 2009

Abstract: In this paper, we examine the Shapiro delay caused by the close approach of an asteroid to the LISA constellation. We find that the probability that such an event occurs at a detectable level during the time interval of the mission is smaller than 1 %.

#### Aug 25, 2009

0908.2043 (/preprints)
2009-08-25, 12:56 

## [0908.2090] A stochastic template placement algorithm for gravitational wave data analysis

Authors: Ian Harry, Bruce Allen, B.S. Sathyaprakash

Date: 14 Aug 2009

Abstract: This paper presents an algorithm for constructing matched-filter template banks in an arbitrary parameter space. The method places templates at random, then removes those which are "too close" together. The properties and optimality of stochastic template banks generated in this manner are investigated for some simple models. The effectiveness of these template banks for gravitational wave searches for binary inspiral waveforms is also examined. The properties of a stochastic template bank are then compared to the deterministically placed template banks that are currently used in gravitational wave data analysis.

#### Aug 25, 2009

0908.2090 (/preprints)
2009-08-25, 12:56 

## [0908.2138] Self-force with (3 1) codes: a primer for numerical relativists

Authors: Ian Vega, Peter Diener, Wolfgang Tichy, Steven Detweiler

Date: 14 Aug 2009

Abstract: Prescriptions for numerical self-force calculations have traditionally been designed for frequency-domain or (1+1) time-domain codes which employ a mode decomposition to facilitate in carrying out a delicate regularization scheme. This has prevented self-force analyses from benefiting from the powerful suite of tools developed and used by numerical relativists for simulations of the evolution of comparable-mass black hole binaries. In this work, we revisit a previously-introduced (3+1) method for self-force calculations, and demonstrate its viability by applying it to the test case of a scalar charge moving in a circular orbit around a Schwarzschild black hole. Two (3+1) codes originally developed for numerical relativity applications were independently employed, and in each we were able to compute the two independent components of the self-force and the energy flux correctly to within $< 1%$. We also demonstrate consistency between $t$-component of the self-force and the scalar energy flux. Our results constitute the first successful calculation of a self-force in a (3+1) framework, and thus open opportunities for the numerical relativity community in self-force analyses and the perturbative modeling of extreme-mass-ratio inspirals.

#### Aug 25, 2009

0908.2138 (/preprints)
2009-08-25, 12:55 

## [0908.1964] Effective Field Theory, Past and Future

Authors: Steven Weinberg

Date: 13 Aug 2009

Abstract: This is a written version of the opening talk at the 6th International Workshop on Chiral Dynamics, at the University of Bern, Switzerland, July 6, 2009, to be published in the proceedings of the Workshop. In it, I reminisce about the early development of effective field theories of the strong interactions, comment briefly on some other applications of effective field theories, and then take up the idea that the Standard Model and General Relativity are the leading terms in an effective field theory. Finally, I cite recent calculations that suggest that the effective field theory of gravitation and matter is asymptotically safe.

#### Aug 25, 2009

0908.1964 (/preprints)
2009-08-25, 12:55 

## [0908.3139] Numerical relativity simulations in the era of the Einstein Telescope

Authors: Mark Hannam, Ian Hawke

Date: 21 Aug 2009

Abstract: Numerical-relativity (NR) simulations of compact binaries are expected to be an invaluable tool in gravitational-wave (GW) astronomy. The sensitivity of future detectors such as the Einstein Telescope (ET) will place much higher demands on NR simulations than first- and second-generation ground-based detectors. We discuss the issues facing compact-object simulations over the next decade, with an emphasis on estimating where the accuracy and parameter space coverage will be sufficient for ET and where significant work is needed.

#### Aug 25, 2009

0908.3139 (/preprints)
2009-08-25, 12:53 

## [0908.2706] Black Holes in Active Galactic Nuclei

Authors: M. J.Valtonen, S. Mikkola, D. Merritt, A. Gopakumar, H. J. Lehto, T. Hyv&#xf6;nen, H. Rampadarath, R. Saunders, M. Basta, R. Hudec

Date: 19 Aug 2009

Abstract: Supermassive black holes are common in centers of galaxies. Among the active galaxies, quasars are the most extreme, and their black hole masses range as high as to $6\cdot 10ˆ{10} M_\odot$. Binary black holes are of special interest but so far OJ287 is the only confirmed case with known orbital elements. In OJ287, the binary nature is confirmed by periodic radiation pulses. The period is twelve years with two pulses per period. The last four pulses have been correctly predicted with the accuracy of few weeks, the latest in 2007 with the accuracy of one day. This accuracy is high enough that one may test the higher order terms in the Post Newtonian approximation to General Relativity. The precession rate per period is $39ˆ\circ.1 \pm 0ˆ\circ.1$, by far the largest rate in any known binary, and the $(1.83\pm 0.01)\cdot 10ˆ{10} M_\odot$ primary is among the dozen biggest black holes known. We will discuss the various Post Newtonian terms and their effect on the orbit solution.
The over 100 year data base of optical variations in OJ287 puts limits on these terms and thus tests the ability of Einstein's General Relativity to describe, for the first time, dynamic binary black hole spacetime in the strong field regime. The quadrupole-moment contributions to the equations of motion allows us to constrain the ‘no-hair’ parameter to be $1.0\:\pm\:0.3$ which supports the black hole no-hair theorem within the achievable precision.

#### Aug 25, 2009

0908.2706 (/preprints)
2009-08-25, 12:52 

## [0908.1780] Ultra Relativistic Particle Collisions

Authors: Matthew W. Choptuik, Frans Pretorius

Date: 12 Aug 2009

Abstract: We present results from numerical solution of the Einstein field equations describing the head-on collision of two solitons boosted to ultra relativistic energies. We show, for the first time, that at sufficiently high energies the collision leads to black hole formation, consistent with hoop conjecture arguments. This implies that the non-linear gravitational interaction between the kinetic energy of the solitons causes gravitational collapse, and that arguments for black hole formation in super-Planck scale particle collisions are robust.

#### Aug 13, 2009

0908.1780 (/preprints)
2009-08-13, 09:25 

## [0908.1654] A Relativistic Motion Integrator: Numerical accuracy and illustration with BepiColombo and Mars-NEXT

Authors: A. Hees, S. Pireaux

Date: 12 Aug 2009

Abstract: Today, the motion of spacecraft is still described by the classical Newtonian equations of motion plus some relativistic corrections. This approach might become cumbersome due to the increasing precision required. We use the Relativistic Motion Integrator (RMI) approach to numerically integrate the native relativistic equations of motion for a spacecraft. The principle of RMI is presented. We compare the results obtained with the RMI method with those from the usual Newton plus correction approach for the orbit of the BepiColombo (around Mercury) and Mars-NEXT (around Mars) orbiters. Finally, we present a numerical study of RMI and we show that the RMI approach is relevant to study the orbit of spacecraft.

#### Aug 13, 2009

0908.1654 (/preprints)
2009-08-13, 09:25 

## [0908.1664] Gravitational self force in extreme mass-ratio inspirals

Authors: Leor Barack

Date: 12 Aug 2009

Abstract: This review is concerned with the gravitational self-force acting on a mass particle in orbit around a large black hole. Renewed interest in this old problem is driven by the prospects of detecting gravitational waves from strongly gravitating binaries with extreme mass ratios. We begin here with a summary of recent advances in the theory of gravitational self-interaction in curved spacetime, and proceed to survey some of the ideas and computational strategies devised for implementing this theory in the case of a particle orbiting a Kerr black hole. We review in detail two of these methods: (i) the standard mode-sum method, in which the metric perturbation is regularized mode-by-mode in a multipole decomposition, and (ii) $m$-mode regularization, whereby individual azimuthal modes of the metric perturbation are regularized in 2+1 dimensions. We discuss several practical issues that arise, including the choice of gauge, the numerical representation of the particle singularity, and how high-frequency contributions near the particle are dealt with in frequency-domain calculations. As an example of a full end-to-end implementation of the mode-sum method, we discuss the computation of the gravitational self-force for eccentric geodesic orbits in Schwarzschild, using a direct integration of the Lorenz-gauge perturbation equations in the time domain. With the computational framework now in place, researchers have recently turned to explore the physical consequences of the gravitational self force; we will describe some preliminary results in this area. An appendix to this review presents, for the first time, a detailed derivation of the regularization parameters necessary for implementing the mode-sum method in Kerr spacetime.

#### Aug 13, 2009

0908.1664 (/preprints)
2009-08-13, 09:25 

## [0908.0961] Coalescing binaries as possible standard candles

Authors: S. Capozziello, M. De Laurentis, M. Formisano

Date: 6 Aug 2009

Abstract: Gravitational waves detected from well-localized inspiraling binaries would allow to determine, directly and independently, both binary luminosity and redshift. In this case, such systems could behave as "standard candles" providing an excellent probe of cosmic distances up to $z <0.1$ and thus complementing other indicators of cosmological distance ladder.

#### Aug 12, 2009

0908.0961 (/preprints)
2009-08-12, 14:47 

## [0908.0117] Tidal effects in the vicinity of a black hole

Authors: A. Cadez, U. Kostic, M. Calvani

Date: 2 Aug 2009

Abstract: The discovery that the Galactic centre emits flares at various wavelengths represents a puzzle concerning their origin, but at the same time it is a relevant opportunity to investigate the environment of the nearest super-massive black hole. In this paper we shall review some of our recent results concerning the tidal evolution of the orbits of low mass satellites around black holes, and the tidal effect during their in-fall. We show that tidal interaction can offer an explanation for transient phenomena like near infra-red and X-ray flares from Sgr A*.

#### Aug 06, 2009

0908.0117 (/preprints)
2009-08-06, 08:35 

## [0908.0244] Timing stability of millisecond pulsars and prospects for gravitational-wave detection

Authors: J.P.W. Verbiest, M. Bailes, W.A. Coles, G.B. Hobbs, W. van Straten, D.J. Champion, F.A. Jenet, R.N. Manchester, N.D.R. Bhat, J.M. Sarkissian, D. Yardley, S. Burke-Spolaor, A.W. Hotan, X.P. You

Date: 3 Aug 2009

Abstract: Analysis of high-precision timing observations of an array of approx. 20 millisecond pulsars (a so-called ''timing array'') may ultimately result in the detection of a stochastic gravitational-wave background. The feasibility of such a detection and the required duration of this type of experiment are determined by the achievable rms of the timing residuals and the timing stability of the pulsars involved. We present results of the first long-term, high-precision timing campaign on a large sample of millisecond pulsars used in gravitational-wave detection projects. We show that the timing residuals of most pulsars in our sample do not contain significant low-frequency noise that could limit the use of these pulsars for decade-long gravitational-wave detection efforts. For our most precisely timed pulsars, intrinsic instabilities of the pulsars or the observing system are shown to contribute to timing irregularities on a five-year timescale below the 100 ns level. Based on those results, realistic sensitivity curves for planned and ongoing timing array efforts are determined. We conclude that prospects for detection of a gravitational-wave background through pulsar timing array efforts within five years to a decade are good.

#### Aug 06, 2009

0908.0244 (/preprints)
2009-08-06, 08:35 

## [0908.0285] Generic tests of the existence of the gravitational dipole radiation and the variation of the gravitational constant

Authors: K. Lazaridis, N. Wex, A. Jessner, M. Kramer, B. W. Stappers, G. H. Janssen, G. Desvignes, M. B. Purver, I. Cognard, G. Theureau, A. G. Lyne, C. A. Jordan, J. A. Zensus

Date: 3 Aug 2009

Abstract: We present results from the high precision timing analysis of the pulsar-white dwarf (WD) binary PSR J1012+5307 using 15 years of multi-telescope data. Observations were performed regularly by the European Pulsar Timing Array (EPTA) network, consisting of Effelsberg, Jodrell Bank, Westerbork and Nan\c{c}ay. All the timing parameters have been improved from the previously published values, most by an order of magnitude. In addition, a parallax measurement of $\pi = 1.2(3)$ mas is obtained for the first time for PSR J1012+5307, being consistent with the optical estimation from the WD companion. Combining improved 3D velocity information and models for the Galactic potential the complete evolutionary Galactic path of the system is obtained. A new intrinsic eccentricity upper limit of $e<8.4\times 10ˆ{-7}$ is acquired, one of the smallest calculated for a binary system and a measurement of the variation of the projected semi-major axis also constrains the system's orbital orientation for the first time. It is shown that PSR J1012+5307 is an ideal laboratory for testing alternative theories of gravity. The measurement of the change of the orbital period of the system of $\dot{P}_{b} = 5(1)\times 10ˆ{-14}$ is used to set an upper limit on the dipole gravitational wave emission that is valid for a wide class of alternative theories of gravity. Moreover, it is shown that in combination with other binary pulsars PSR J1012+5307 is an ideal system to provide self-consistent, generic limits, based only on millisecond pulsar data, for the dipole radiation and the variation of the gravitational constant $\dot{G}$.

#### Aug 06, 2009

0908.0285 (/preprints)
2009-08-06, 08:35 

## [0908.0004] The gravitational S-matrix

Authors: Steven B. Giddings, Rafael A. Porto

Date: 3 Aug 2009

Abstract: We investigate the hypothesized existence of an S-matrix for gravity, and some of its expected general properties. We first discuss basic questions regarding existence of such a matrix, including those of infrared divergences and description of asymptotic states. Distinct scattering behavior occurs in the Born, eikonal, and strong gravity regimes, and we describe aspects of both the partial wave and momentum space amplitudes, and their analytic properties, from these regimes. Classically the strong gravity region would be dominated by formation of black holes, and we assume its unitary quantum dynamics is described by corresponding resonances. Masslessness limits some powerful methods and results that apply to massive theories, though a continuation path implying crossing symmetry plausibly still exists. Physical properties of gravity suggest nonpolynomial amplitudes, although crossing and causality constrain (with modest assumptions) this nonpolynomial behavior, particularly requiring a polynomial bound in complex s at fixed physical momentum transfer. We explore the hypothesis that such behavior corresponds to a nonlocality intrinsic to gravity, but consistent with unitarity, analyticity, crossing, and causality.

#### Aug 06, 2009

0908.0004 (/preprints)
2009-08-06, 08:33 

## [0908.0228] Non-Gaussianity analysis of GW background made by short-duration burst signals

Authors: Naoki Seto

Date: 3 Aug 2009

Abstract: We study an observational method to analyze non-Gaussianity of a gravitational wave (GW) background made by superposition of weak burst signals. The proposed method is based on fourth-order correlations of data from four detectors, and might be useful to discriminate the origin of a GW background. With a formulation newly developed to discuss geometrical aspects of the correlations, it is found that the method provides us with linear combinations of two interesting parameters, I_2 and V_2 defined by the Stokes parameters of individual GW burst signals. We also evaluate sensitivities of specific detector networks to these parameters.

#### Aug 06, 2009

0908.0228 (/preprints)
2009-08-06, 08:33 

## [0908.0365] The Hilbert Lagrangian and Isometric Embedding: Spherically Symmetric Static Cases and Cosmological Solutions

Authors: Frank B. Estabrook

Date: 3 Aug 2009

Abstract: We formulate, and solve in several symmetric cases, the classical field-theoretic dynamics that arises when the Hilbert-Einstein Lagrangian is taken as the action for isometric embedding of 4-spaces into ten flat dimensions. Its variation gives the Euler-Lagrange equations of a well- posed multicontact field theory. The Hilbert Lagrangian as usually varied over just the intrinsic curvature structure of a 4-space yields only a subset of this dynamics, viz., solutions whose initial conditions constrain them to be Ricci-flat. We conjecture that there may be a classical correspondence with the hidden dimensions of brane theory, and that perhaps this extended general relativistic dynamics holds in extreme circumstances where it can be interpreted as including a sort of dark energy, although no term with a cosmological constant is included in the Lagrangian. As a multicontact system, canonical quantization should be straightforward.

#### Aug 06, 2009

0908.0365 (/preprints)
2009-08-06, 08:33 

## [0908.0209] Towards Relativistic Atomic Physics and Post-Minkowskian Gravitational Waves

Authors: Luca Lusanna (INFN)

Date: 3 Aug 2009

Abstract: A review is given of the formulation of relativistic atomic theory, in which there is an explicit realization of the Poincare' generators, both in the inertial and in the non-inertial rest-frame instant form of dynamics in Minkowski space-time. This implies the need to solve the problem of the relativistic center of mass of an isolated system and to describe the transitions from different conventions for clock synchronization, namely for the identifications of instantaneous 3-spaces, as gauge transformations. These problems, stemming from the Lorentz signature of space-time, are a source of non-locality, which induces a spatial non-separability in relativistic quantum mechanics, with implications for relativistic entanglement. Then the classical system of charged particles plus the electro-magnetic field is studied in the framework of ADM canonical tetrad gravity in asymptotically Minkowskian space-times admitting the ADM Poincare' group at spatial infinity, which allows to get the general relativistic extension of the non-inertial rest frames of special relativity. The use of the York canonical basis allows to disentangle the tidal degrees of freedom of the gravitational field from the inertial ones. The York time is the inertial gauge variable describing the general relativistic remnant of the gauge freedom in clock synchronization. However now each solution of Einstein's equations dynamically determines a preferred notion of instantaneous 3-spaces. The linearization of this canonical formulation in the weak field approximation will allow to find Hamiltonian Post-Minkowskian gravitational waves with an asymptotic background and without Post-Newtonian expansion in non-harmonic 3-orthogonal gauges.

#### Aug 06, 2009

0908.0209 (/preprints)
2009-08-06, 08:33 

## [0907.5450] Exploring intermediate and massive black-hole binaries with the Einstein Telescope

Authors: Jonathan R. Gair, Ilya Mandel, M. Coleman Miller, Marta Volonteri

Date: 31 Jul 2009

Abstract: We discuss the capability of a third-generation ground-based detector such as the Einstein Telescope (ET) to enhance our astrophysical knowledge through detections of gravitational waves emitted by binaries including intermediate-mass and massive black holes. The design target for such instruments calls for improved sensitivity at low frequencies, specifically in the ~ 1-10 Hz range. This will allow the detection of gravitational waves generated in binary systems containing black holes of intermediate mass, ~ 100-1000 solar masses. We primarily discuss two different source types -- mergers between two intermediate mass black holes (IMBHs) of comparable mass, and intermediate-mass-ratio inspirals (IMRIs) of smaller compact objects with mass ~ 1-10 solar masses into IMBHs. IMBHs may form via two channels: (i) in dark matter halos at high redshift through direct collapse or the collapse of very massive metal-poor Population III stars, or (ii) via runaway stellar collisions in globular clusters. In this paper, we discuss both formation channels, and both classes of merger in each case. We review existing rate estimates where these exist in the literature, and provide some new calculations for the approximate numbers of events that will be seen by a detector like the ET. These results indicate that the ET may see a few to a few thousand comparable-mass IMBH mergers and as many as several hundred IMRI events per year. These observations will significantly enhance our understanding of galactic black-hole growth, of the existence and properties of IMBHs and of the astrophysics of globular clusters. We finish our review with a discussion of some more speculative sources of gravitational waves for the ET, including hypermassive white dwarfs and eccentric compact-object binaries.

#### Aug 06, 2009

0907.5450 (/preprints)
2009-08-06, 08:33 

## [0908.0290] The performance of arm locking in LISA

Authors: Kirk McKenzie, Robert E. Spero, Daniel A. Shaddock

Date: 3 Aug 2009

Abstract: For the laser interferometer space antenna (LISA) to reach it's design sensitivity, the coupling of the free running laser frequency noise to the signal readout must be reduced by more than 14 orders of magnitude. One technique employed to reduce the laser frequency noise will be arm locking, where the laser frequency is locked to the LISA arm length. This paper details an implementation of arm locking, studies orbital effects, the impact of errors in the Doppler knowledge, and noise limits. The noise performance of arm locking is calculated with the inclusion of the dominant expected noise sources: ultra stable oscillator (clock) noise, spacecraft motion, and shot noise. Studying these issues reveals that although dual arm locking [A. Sutton & D. A Shaddock, Phys. Rev. D 78, 082001 (2008).] has advantages over single (or common) arm locking in terms of allowing high gain, it has disadvantages in both laser frequency pulling and noise performance. We address this by proposing a hybrid sensor, retaining the benefits of common and dual arm locking sensors. We present a detailed design of an arm locking controller and perform an analysis of the expected performance when used with and without laser pre-stabilization. We observe that the sensor phase changes beneficially near unity-gain frequencies of the arm-locking controller, allowing a factor of 10 more gain than previously believed, without degrading stability. We show that the LISA frequency noise goal can be realized with arm locking and Time-Delay Interferometry only, without any form of pre-stabilization.

#### Aug 06, 2009

0908.0290 (/preprints)
2009-08-06, 08:33 

## [0908.0023] Modeling Flows Around Merging Black Hole Binaries

Authors: James R. van Meter, John H. Wise, M. Coleman Miller, Christopher S. Reynolds, Joan M. Centrella, John G. Baker, William D. Boggs, Bernard J. Kelly, Sean T. McWilliams

Date: 31 Jul 2009

Abstract: Coalescing massive black hole binaries are produced by the mergers of galaxies. The final stages of the black hole coalescence produce strong gravitational radiation that can be detected by the space-borne LISA. In cases where the black hole merger takes place in the presence of gas and magnetic fields, various types of electromagnetic signals may also be produced. Modeling such electromagnetic counterparts of the final merger requires evolving the behavior of both gas and fields in the strong-field regions around the black holes. We have taken a step towards solving this problem by mapping the flow of pressureless matter in the dynamic, 3-D general relativistic spacetime around the merging black holes. We find qualitative differences in collision and outflow speeds, including a signature of the merger when the net angular momentum of the matter is low, between the results from single and binary black holes, and between nonrotating and rotating holes in binaries. If future magnetohydrodynamic results confirm these differences, it may allow assessment of the properties of the binaries as well as yielding an identifiable electromagnetic counterpart to the attendant gravitational wave signal.

#### Aug 06, 2009

0908.0023 (/preprints)
2009-08-06, 08:33