[1009.5882] On the relevance of gravitational self-force corrections on parameter estimation errors for extreme-mass-ratio inspirals

Authors: E. A. Huerta, Jonathan R Gair

Date: 29 Sep 2010

Abstract: It is not currently clear how important it will be to include conservative self-force (SF) corrections in the models for extreme-mass-ratio inspiral (EMRI) waveforms that will be used to detect such signals in LISA (Laser Interferometer Space Antenna) data. These proceedings will address this issue for circular-equatorial inspirals using an approximate EMRI model that includes conservative corrections at leading post-Newtonian order. We will present estimates of the magnitude of the parameter estimation errors that would result from omitting conservative corrections, and compare these to the errors that will arise from noise fluctuations in the detector. We will also use this model to explore the relative importance of the second-order radiative piece of the SF, which is not presently known.

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Sep 29, 2010

1009.5882 (/preprints)
2010-09-29, 21:01 [edit]


[1009.5514] Varying constants, Gravitation and Cosmology

Authors: Jean-Philippe Uzan

Date: 28 Sep 2010

Abstract: Fundamental constants are a cornerstone of our physical laws. Any constant varying in space and/or time would reflect the existence of an almost massless field that couples to matter. This will induce a violation of the universality of free fall. It is thus of utmost importance for our understanding of gravity and of the domain of validity of general relativity to test for their constancy. We thus detail the relations between the constants, the tests of the local position invariance and of the universality of free fall. We then review the main experimental and observational constraints that have been obtained from atomic clocks, the Oklo phenomenon, Solar system observations, meteorites dating, quasar absorption spectra, stellar physics, pulsar timing, the cosmic microwave background and big bang nucleosynthesis. At each step we describe the basics of each system, its dependence with respect to the constants, the known systematic effects and the most recent constraints that have been obtained. We then describe the main theoretical frameworks in which the low-energy constants may actually be varying and we focus on the unification mechanisms and the relations between the variation of different constants. To finish, we discuss the more speculative possibility of understanding their numerical values and the apparent fine-tuning that they confront us with.

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Sep 29, 2010

1009.5514 (/preprints)
2010-09-29, 15:36 [edit]


[1009.5042] Gravitational waves from binaries on unbound orbits

Authors: János Majár, Péter Forgács, Mátyás Vasúth

Date: 25 Sep 2010

Abstract: A generalized true anomaly-type parametrization, convenient to describe both bound and open orbits of a two-body system in general relativity is introduced. A complete description of the time evolution of both the radial and of the angular equations of a binary system taking into account the first order post-newtonian (1PN) is given. The gravitational radiation field emitted by the system is computed in the 1PN approximation including higher multipole moments beyond the standard quadrupole term. The gravitational waveforms in the time domain are explicitly given up to the 1PN order for unbound orbits, but the results are also illustrated on binaries on elliptic orbits with special attention given to the effects of eccentricity.

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Sep 29, 2010

1009.5042 (/preprints)
2010-09-29, 15:36 [edit]


[1009.5243] Relic gravitational waves: latest revisions and preparations for new data

Authors: Wen Zhao, L. P. Grishchuk

Date: 27 Sep 2010

Abstract: The forthcoming release of data from the Planck mission, and possibly from the next round of Wilkinson Microwave Anisotropy Probe (WMAP) observations, make it necessary to revise the evaluations of relic gravitational waves in the existing data and, at the same time, to refine the assumptions and data analysis techniques in preparation for the arrival of new data. We reconsider with the help of the commonly used CosmoMC numerical package the previously found indications of relic gravitational waves in the 7-year (WMAP7) data. The CosmoMC approach reduces the confidence of these indications from approximately 2$\sigma$ level to approximately 1$\sigma$ level, but the indications do not disappear altogether. We critically analyze the assumptions that are currently used in the Cosmic Microwave Background (CMB) data analyses and outline the strategy that should help avoid the oversight of relic gravitational waves in the CMB data. The prospects of confident detection of relic gravitational waves by the Planck satellite have worsened, but they are still good. It appears that more effort will be required in order to mitigate the foreground contamination.

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Sep 29, 2010

1009.5243 (/preprints)
2010-09-29, 15:36 [edit]


[1009.5523] On the metric structure of space-time

Authors: Jochen Rau

Date: 28 Sep 2010

Abstract: I present an analysis of the physical assumptions needed to obtain the metric structure of space-time. For this purpose I combine the axiomatic approach pioneered by Robb with ideas drawn from works on Weyl's "Raumproblem". The concept of a Lorentzian manifold is replaced by the weaker concept of an "event manifold", defined in terms of volume element, causal structure and affine connection(s). Exploiting properties of its structure group, I show that distinguishing Lorentzian manifolds from other classes of event manifolds requires the key idea of general relativity: namely that the manifold's physical structure, rather than being fixed, is itself a variable.

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Sep 29, 2010

1009.5523 (/preprints)
2010-09-29, 15:36 [edit]


[1009.4919] Post-1-Newtonian quadrupole tidal interactions in binary systems

Authors: Justin Vines, Eanna E. Flanagan

Date: 24 Sep 2010

Abstract: We consider orbital-tidal coupling in a binary stellar system to post-1-Newtonian order. We derive the orbital equations of motion for bodies with spins and mass quadrupole moments and show that they conserve the total linear momentum of the binary. Momentum conservation also allows us to specialize our analysis to the system's center-of-mass-energy frame; we find the binary's relative equation of motion in this frame and also present a generalized Lagrangian from which it can be derived. We then specialize to the case in which the quadrupole moment in the adiabatically induced by the tidal field. We show how the adiabatic dynamics for the quadrupole can be incorporated into our action principle and present the simplified orbital equations of motion and conserved energy for the adiabatic case. These results are relevant to the gravitational wave signal of inspiralling binary neutron stars.

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Sep 26, 2010

1009.4919 (/preprints)
2010-09-26, 19:46 [edit]


[1009.4923] Transient resonances in the inspirals of point particles into black holes

Authors: Eanna E. Flanagan (Cornell), Tanja Hinderer (Caltech)

Date: 24 Sep 2010

Abstract: We show that transient resonances occur in the two body problem in general relativity, in the highly relativistic, extreme mass-ratio regime for spinning black holes. These resonances occur when the ratio of polar and radial orbital frequencies, which is slowly evolving under the influence of gravitational radiation reaction, passes through a low order rational number. At such points, the adiabatic approximation to the orbital evolution breaks down, and there is a brief but order unity correction to the inspiral rate. Corrections to the gravitational wave signal's phase due to resonance effects scale as the square root of the inverse of mass of the small body, and thus become large in the extreme-mass-ratio limit, dominating over all other post-adiabatic effects. The resonances make orbits more sensitive to changes in initial data (though not quite chaotic), and are genuine non-perturbative effects that are not seen at any order in a standard post-Newtonian expansion. Our results apply to an important potential source of gravitational waves, the gradual inspiral of white dwarfs, neutron stars, or black holes into much more massive black holes. It is hoped to exploit observations of these sources to map the spacetime geometry of black holes. However, such mapping will require accurate models of binary dynamics, which is a computational challenge whose difficulty is significantly increased by resonance effects. We estimate that the resonance phase shifts will be of order a few tens of cycles for mass ratios $\sim 10ˆ{-6}$, by numerically evolving fully relativistic orbital dynamics supplemented with an approximate, post-Newtonian self-force.

abs pdf

Sep 26, 2010

1009.4923 (/preprints)
2010-09-26, 19:45 [edit]


[1009.2755] Error estimation in astronomy: A guide

Authors: Rene Andrae

Date: 14 Sep 2010

Abstract: Estimating errors is a crucial part of any scientific analysis. Whenever a parameter is estimated (model-based or not), an error estimate is necessary. Any parameter estimate that is given without an error estimate is meaningless. Nevertheless, many (undergraduate or graduate) students have to teach such methods for error estimation to themselves when working scientifically for the first time. This manuscript presents an easy-to-understand overview of different methods for error estimation that are applicable to both model-based and model-independent parameter estimates. These methods are not discussed in detail, but their basics are briefly outlined and their assumptions carefully noted. In particular, the methods for error estimation discussed are grid search, varying $\chiˆ2$, the Fisher matrix, Monte-Carlo methods, error propagation, data resampling, and bootstrapping. Finally, a method is outlined how to propagate measurement errors through complex data-reduction pipelines.

abs pdf

Sep 23, 2010

1009.2755 (/preprints)
2010-09-23, 06:49 [edit]


[1009.3225] Phenomenology of the Lense-Thirring effect in the Solar System

Authors: L. Iorio, H.I.M. Lichtenegger, M.L. Ruggiero, C. Corda

Date: 16 Sep 2010

Abstract: Recent years have seen increasing efforts to directly measure some aspects of the general relativistic gravitomagnetic interaction in several astronomical scenarios in the solar system. After briefly overviewing the concept of gravitomagnetism from a theoretical point of view, we review the performed or proposed attempts to detect the Lense-Thirring effect affecting the orbital motions of natural and artificial bodies in the gravitational fields of the Sun, Earth, Mars and Jupiter. In particular, we will focus on the evaluation of the impact of several sources of systematic uncertainties of dynamical origin to realistically elucidate the present and future perspectives in directly measuring such an elusive relativistic effect.

abs pdf

Sep 23, 2010

1009.3225 (/preprints)
2010-09-23, 06:08 [edit]


[1009.3021] General Relativistic Description of the Observed Galaxy Power Spectrum: Do We Understand What We Measure?

Authors: Jaiyul Yoo (Harvard/Zürich)

Date: 15 Sep 2010

Abstract: We extend the general relativistic description of galaxy clustering developed in Yoo, Fitzpatrick, and Zaldarriaga (2009). For the first time we provide a fully general relativistic description of the observed matter power spectrum and the observed galaxy power spectrum with the linear bias ansatz. It is significantly different from the standard Newtonian description on large scales and especially its measurements on large scales can be misinterpreted as the detection of the primordial non-Gaussianity even in the absence thereof. The key difference in the observed galaxy power spectrum arises from the real-space matter fluctuation defined as the matter fluctuation at the hypersurface of the observed redshift. As opposed to the standard description, the shape of the observed galaxy power spectrum evolves in redshift, providing additional cosmological information. While the systematic errors in the standard Newtonian description are negligible in the current galaxy surveys at low redshift, correct general relativistic description is essential for understanding the galaxy power spectrum measurements on large scales in future surveys with redshift depth z>3. We discuss ways to improve the detection significance in the current galaxy surveys and comment on applications of our general relativistic formalism in future surveys.

abs pdf

Sep 23, 2010

1009.3021 (/preprints)
2010-09-23, 06:08 [edit]


[1009.4401] Rotation and Spin in Physics

Authors: R. F. O'Connell

Date: 22 Sep 2010

Abstract: We delineate the role of rotation and spin in physics, discussing in order Newtonian classical physics, special relativity, quantum mechanics, quantum electrodynamics and general relativity. In the latter case, we discuss the generalization of the Kepler formula to post-Newtonian order $(cˆ{-2}$) including spin effects and two-body effects. Experiments which verify the theoretical results for general relativistic spin-orbit effects are discussed as well as efforts being made to verify the spin-spin effects.

abs pdf

Sep 22, 2010

1009.4401 (/preprints)
2010-09-22, 19:31 [edit]


[1009.4192] Astrometric Effects of a Stochastic Gravitational Wave Background

Authors: Laura G. Book (1), Éanna É. Flanagan (2), ((1) California Institute of Technology, (2) Cornell University)

Date: 21 Sep 2010

Abstract: A stochastic gravitational wave background causes the apparent positions of distant sources to fluctuate, with angular deflections of order the characteristic strain amplitude of the gravitational waves. These fluctuations may be detectable with high precision astrometry, as first suggested by Braginsky et al. in 1990. Several researchers have made order of magnitude estimates of the upper limits obtainable on the gravitational wave spectrum \Omega_gw(f), at frequencies of order f ~ 1 yrˆ-1, both for the future space-based optical interferometry missions GAIA and SIM, and for VLBI interferometry in radio wavelengths with the SKA. For GAIA, tracking N ~ 10ˆ6 sources over a time of T ~ 1 yr with an angular accuracy of \Delta \theta ~ 10 \mu as would yield a sensitivity level of \Omega_gw ~ (\Delta \theta)ˆ2/(N Tˆ2 H_0ˆ2) ~ 10ˆ-6, which would be comparable with pulsar timing. In this paper we take a first step toward firming up these estimates by computing in detail the statistical properties of the angular deflections caused by a stochastic background. We compute analytically the two point correlation function of the deflections on the sphere, and the spectrum as a function of frequency and angular scale. The fluctuations are concentrated at low frequencies (for a scale invariant stochastic background), and at large angular scales, starting with the quadrupole. The magnetic-type and electric-type pieces of the fluctuations have equal amounts of power.

abs pdf

Sep 22, 2010

1009.4192 (/preprints)
2010-09-22, 19:31 [edit]


[1009.3968] Electrodynamics in accelerated frames revisited

Authors: J. W. Maluf, S. C. Ulhoa

Date: 20 Sep 2010

Abstract: Maxwell's equations are formulated in arbitrary moving frames by means of tetrad fields, which are interpreted as reference frames adapted to observers in space-time. We assume the existence of a general distribution of charges and currents in an inertial frame. Tetrad fields are used to project the electromagnetic fields and sources on accelerated frames. The purpose is to study several configurations of fields and observers that in the literature are understood as paradoxes. For instance, are the two situations, (i) an accelerated charge in an inertial frame, and (ii) a charge at rest in an inertial frame described from the perspective of an accelerated frame, physically equivalent? Is the electromagnetic radiation the same in both frames? Normally in the analysis of these paradoxes the electromagnetic fields are transformed to (uniformly) accelerated frames by means of a coordinate transformation of the Faraday tensor. In the present approach coordinate and frame transformations are disentangled, and the electromagnetic field in the accelerated frame is obtained through a frame (local Lorentz) transformation. Consequently the fields in the inertial and accelerated frames are described in the same coordinate system. This feature allows the investigation of paradoxes such as the one mentioned above.

abs pdf

Sep 22, 2010

1009.3968 (/preprints)
2010-09-22, 08:04 [edit]


[1008.0399] Massive Black Hole Binary Systems in Hierarchical Scenario of Structure Formation

Authors: Eduardo S. Pereira, Oswaldo D. Miranda

Date: 2 Aug 2010

Abstract: The hierarchical scenario of structure formation describes how objects like galaxies and galaxy clusters are formed by mergers of small objects. In this scenario, mergers of galaxies can lead to the formation of massive black hole (MBH) binary systems. On the other hand, the merger of two MBH could produce a gravitational wave signal detectable, in principle, by the Laser Interferometer Space Antenna (LISA). In the present work, we use the Press-Schechter formalism, and its extension, to describe the merger rate of haloes which contain massive black holes. Here, we do not study the gravitational wave emission of these systems. However, we present an initial study to determine the number of systems formed via mergers that could permit, in a future extension of this work, the calculation of the signature in gravitational waves of these systems.

abs pdf

Sep 15, 2010

1008.0399 (/preprints)
2010-09-15, 05:52 [edit]


[1009.2702] An Atomic Gravitational Wave Interferometric Sensor in Low Earth Orbit (AGIS-LEO)

Authors: Jason M. Hogan, David M. S. Johnson, Susannah Dickerson, Tim Kovachy, Alex Sugarbaker, Sheng-wey Chiow, Peter W. Graham, Mark A. Kasevich, Babak Saif, Surjeet Rajendran, Philippe Bouyer, Bernard D. Seery, Lee Feinberg, Ritva Keski-Kuha

Date: 14 Sep 2010

Abstract: We propose an atom interferometer gravitational wave detector in low Earth orbit (AGIS-LEO). Gravitational waves can be observed by comparing a pair of atom interferometers separated over a ~30 km baseline. In the proposed configuration, one or three of these interferometer pairs are simultaneously operated through the use of two or three satellites in formation flight. The three satellite configuration allows for the increased suppression of multiple noise sources and for the detection of stochastic gravitational wave signals. The mission will offer a strain sensitivity of < 10ˆ(-18) / Hzˆ(½) in the 50 mHz - 10 Hz frequency range, providing access to a rich scientific region with substantial discovery potential. This band is not currently addressed with the LIGO or LISA instruments. We analyze systematic backgrounds that are relevant to the mission and discuss how they can be mitigated at the required levels. Some of these effects do not appear to have been considered previously in the context of atom interferometry, and we therefore expect that our analysis will be broadly relevant to atom interferometric precision measurements. Finally, we present a brief conceptual overview of shorter-baseline (< 100 m) atom interferometer configurations that could be deployed as proof-of-principle instruments on the International Space Station (AGIS-ISS) or an independent satellite.

abs pdf

Sep 15, 2010

1009.2702 (/preprints)
2010-09-15, 05:51 [edit]


[1009.2533] Inspiral of Generic Black Hole Binaries: Spin, Precession, and Eccentricity

Authors: Janna Levin, Hugo Contreras

Date: 13 Sep 2010

Abstract: We compile the equations of motion describing the most general black hole binaries as computed by Will and collaborators. We use the equations converted to Hamiltonian variables to consider spinning and precessing and eccentric pairs. We find that while spin-spin coupling corrections can destroy constant radius orbits in principle, the effect is so small that orbits will reliably tend to quasi-spherical as angular momentum and energy are lost to gravitational radiation. Still, highly eccentric pairs can retain eccentricity by the time of plunge. We also show that three natural frequencies of an orbit demonstrating both spin precession and perihelion precession are the frequency of angular motion in the orbital plane, the frequency of the plane precession, and the frequency of radial oscillations. These three shape the waveform. The pattern of energy lost during the inspiral is also directly related to these same natural harmonics.

abs pdf

Sep 15, 2010

1009.2533 (/preprints)
2010-09-15, 05:49 [edit]


[1009.2263] Optical Synoptic Telescopes: New Science Frontiers

Authors: J. Anthony Tyson

Date: 12 Sep 2010

Abstract: Over the past decade, sky surveys such as the Sloan Digital Sky Survey have proven the power of large data sets for answering fundamental astrophysical questions. This observational progress, based on a synergy of advances in telescope construction, detectors, and information technology, has had a dramatic impact on nearly all fields of astronomy, and areas of fundamental physics. The next-generation instruments, and the surveys that will be made with them, will maintain this revolutionary progress. The hardware and computational technical challenges and the exciting science opportunities are attracting scientists and engineers from astronomy, optics, low-light-level detectors, high-energy physics, statistics, and computer science. The history of astronomy has taught us repeatedly that there are surprises whenever we view the sky in a new way. This will be particularly true of discoveries emerging from a new generation of sky surveys. Imaging data from large ground-based active optics telescopes with sufficient etendue can address many scientific missions simultaneously. These new investigations will rely on the statistical precision obtainable with billions of objects. For the first time, the full sky will be surveyed deep and fast, opening a new window on a universe of faint moving and distant exploding objects as well as unraveling the mystery of dark energy.

abs pdf

Sep 14, 2010

1009.2263 (/preprints)
2010-09-14, 13:33 [edit]


[1009.2484] Gravitational wave signatures from kink proliferation on cosmic (super-) strings

Authors: P. Binetruy, A. Bohe, T. Hertog, D.A. Steer

Date: 13 Sep 2010

Abstract: Junctions on cosmic string loops give rise to the proliferation of sharp kinks. We study the effect of this proliferation on the gravitational wave (GW) signals emitted from string networks with junctions, assuming a scaling solution. We calculate the rate of occurrence and the distribution in amplitude of the GW bursts emitted at cusps and kinks in the frequency bands of LIGO and LISA as a function of the string tension, the number of sharp kinks on loops with junctions and the fraction of loops in the cosmological network which have junctions. Combining our results with current observational constraints, we find that pulsar data rule out a significant number of kinks on loops for strings with tensions G\mu > 10ˆ{-12}. By contrast, for smaller tensions current observations allow for a large number of kinks on loops. If this is the case, the incoherent superposition of small bursts emitted at kink-kink encounters leads to an enhanced GW background that hides the strong individual bursts from kinks and cusps.

abs pdf

Sep 14, 2010

1009.2484 (/preprints)
2010-09-14, 09:02 [edit]


[1009.2468] Accurate evolutions of inspiralling and magnetized neutron-stars: equal-mass binaries

Authors: Bruno Giacomazzo, Luciano Rezzolla, Luca Baiotti

Date: 13 Sep 2010

Abstract: By performing new, long and numerically accurate general-relativistic simulations of magnetized, equal-mass neutron-star binaries, we investigate the role that realistic magnetic fields may have in the evolution of these systems. In particular, we study the evolution of the magnetic fields and show that they can influence the survival of the hypermassive-neutron star produced at the merger by accelerating its collapse to a black hole. We also provide evidence that even if purely poloidal initially, the magnetic fields produced in the tori surrounding the black hole have toroidal and poloidal components of equivalent strength. When estimating the possibility that magnetic fields could have an impact on the gravitational-wave signals emitted by these systems either during the inspiral or after the merger we conclude that for realistic magnetic-field strengths B<~1e12 G such effects could be detected, but only marginally, by detectors such as advanced LIGO or advanced Virgo. However, magnetically induced modifications could become detectable in the case of small-mass binaries and with the development of gravitational-wave detectors, such as the Einstein Telescope, with much higher sensitivities at frequencies larger than ~2 kHz.

abs pdf

Sep 14, 2010

1009.2468 (/preprints)
2010-09-14, 09:02 [edit]


[1009.1985] Intermediate-mass-ratio-inspirals in the Einstein Telescope: I. Signal-to-noise ratio calculations

Authors: E.A. Huerta, Jonathan R. Gair

Date: 10 Sep 2010

Abstract: The Einstein Telescope (ET) is a proposed third generation ground-based interferometer, for which the target is a sensitivity that is a factor of ten better than Advanced LIGO and a frequency range that extends down to about 1Hz. ET will provide opportunities to test Einstein's theory of relativity in the strong field and will realize precision gravitational wave astronomy with a thousandfold increase in the expected number of events over the advanced ground-based detectors. A design study for ET is currently underway, so it is timely to assess the science that could be done with such an instrument. This paper is the first in a series that will carry out a detailed study of intermediate-mass-ratio inspirals (IMRIs) for ET. In the context of ET, an IMRI is the inspiral of a neutron star or stellar-mass black hole into an intermediate mass black hole (IMBH). In this paper we focus on the development of IMRI waveform models for circular and equatorial inspirals. We consider two approximations for the waveforms, which both incorporate the inspiral, merger and ringdown phases in a consistent way. One approximation uses the Effective One Body (EOB) approach, but at present this applies only to inspirals into non-spinning IMBHs. The second approximation, valid for IMBHs of arbitrary spin, uses the transition model of Ori and Thorne [1] to describe the merger and this is then matched smoothly onto a ringdown waveform. In this paper, we use both waveform models to compute signal-to-noise ratios (SNRs) for IMRI sources detectable by ET. At a redshift of z=1, we find typical SNRs for IMRI systems with masses 1.4+100 solar masses, 10+100 solar masses, 1.4+500 solar masses and 10+500 solar masses of about 10-25, 40-80, 3-15 and 10-60, respectively. We also find that the two models make predictions for non-spinning inspirals that are consistent to about ten percent.

abs pdf

Sep 13, 2010

1009.1985 (/preprints)
2010-09-13, 08:13 [edit]


[1009.1876] Einstein's action in terms of Newtonian fields

Authors: Barak Kol, Michael Smolkin

Date: 9 Sep 2010

Abstract: We obtain the full non-quadratic Einstein-Hilbert action in terms of the "Newtonian" or non-relativistic gravitational fields and find a fairly simple expression. By exchanging time and space this becomes the full non-quadratic action for massive Kaluza-Klein gravity.

abs pdf

Sep 13, 2010

1009.1876 (/preprints)
2010-09-13, 08:13 [edit]


[1009.1870] Relativistic encounters of more than two black holes

Authors: Pau Amaro-Seoane, Marc Dewi Freitag

Date: 9 Sep 2010

Abstract: Two coalescing black holes (BHs) represent a conspicuous source of gravitational waves (GWs). The merger involves 17 parameters in the general case of Kerr BHs, so that a successful identification and parameter extraction of the information encoded in the waves will provide us with a detailed description of the physics of BHs. A search based on matched-filtering for characterization and parameter extraction requires the development of some $10ˆ{15}$ waveforms. If a third additional BH perturbed the system, the waveforms would not be applicable, and we would need to increase the number of templates required for a valid detection. In this letter, we calculate the probability that more than two BHs interact in the regime of strong relativity in a dense stellar cluster. We determine the physical properties necessary in a stellar system for three black holes to have a close encounter in this regime and also for an existing binary of two BHs to have a strong interaction with a third hole. In both cases the event rate is negligible. While dense stellar systems such as galactic nuclei, globular clusters and nuclear stellar clusters are the breeding grounds for the sources of gravitational waves that ground-based and space-borne detectors like Advanced LIGO and LISA will be exploring, the analysis of the waveforms in full general relativity needs only to evaluate the two-body problem. This reduces the number of templates of waveforms to create by orders of magnitude.

abs pdf

Sep 13, 2010

1009.1870 (/preprints)
2010-09-13, 08:12 [edit]


[1009.1791] Identifying the Host Galaxy of Gravitational Wave Signals

Authors: Laura K Nuttall, Patrick J Sutton

Date: 9 Sep 2010

Abstract: One of the goals of the current LIGO-GEO-Virgo science run is to identify transient gravitational wave (GW) signals in near real time to allow follow-up electromagnetic (EM) observations. An EM counterpart could increase the confidence of the GW detection and provide insight into the nature of the source. Current GW-EM campaigns target potential host galaxies based on overlap with the GW sky error box. We propose a new statistic to identify the most likely host galaxy, ranking galaxies based on their position, distance, and luminosity. We test our statistic with Monte Carlo simulations of GWs produced by coalescing binaries of neutron stars (NS) and black holes (BH), one of the most promising sources for ground-based GW detectors. Considering signals accessible to current detectors, we find that when imaging a single galaxy, our statistic correctly identifies the true host ~20% to ~50% of the time, depending on the masses of the binary components. With five narrow-field images the probability of imaging the true host increases to ~50% to ~80%. When collectively imaging groups of galaxies using large field-of-view telescopes, the probability improves to ~30% to ~60% for a single image and to ~70% to ~90% for five images. For the advanced generation of detectors (c. 2015+), and considering binaries within 100 Mpc (the reach of the galaxy catalogue used), the probability is ~40% for one narrow-field image, ~75% for five narrow-field images, ~65% for one wide-field image, and ~95% for five wide-field images, irrespective of binary type.

abs pdf

Sep 10, 2010

1009.1791 (/preprints)
2010-09-10, 00:29 [edit]


[1009.1240] Stochastic background of gravitational waves emitted by magnetars

Authors: Stefania Marassi, Riccardo Ciolfi, Raffaella Schneider, Luigi Stella, Valeria Ferrari

Date: 7 Sep 2010

Abstract: Two classes of high energy sources in our galaxy are believed to host magnetars, neutron stars whose emission results from the dissipation of their magnetic field. The extremely high magnetic field of magnetars distorts their shape, and causes the emission of a conspicuous gravitational waves signal if rotation is fast and takes place around a different axis than the symmetry axis of the magnetic distortion. Based on a numerical model of the cosmic star formation history, we derive the cosmological background of gravitational waves produced by magnetars, when they are very young and fast spinning. We adopt different models for the configuration and strength of the internal magnetic field (which determines the distortion) as well as different values of the external dipole field strength (which governs the spin evolution of magnetars over a wide range of parameters). We find that the expected gravitational wave background differs considerably from one model to another. The strongest signals are generated for magnetars with very intense toroidal internal fields ($\sim 10ˆ{16}$ G range) and external dipole fields of $\sim 10ˆ{14}$, as envisaged in models aimed at explaining the properties of the Dec 2004 giant flare from SGR 1806-20. Such signals should be easily detectable with third generation ground based interferometers such as the Einstein Telescope.

abs pdf

Sep 07, 2010

1009.1240 (/preprints)
2010-09-07, 18:18 [edit]


[1009.1138] The Past, Present and Future of the Resonant-Mass Gravitational Wave Detectors

Authors: Odylio Denys Aguiar

Date: 6 Sep 2010

Abstract: Resonant-mass gravitational waves detectors are reviewed from the concept of gravitational waves and its mathematical derivation, using Einstein's general relativity, to the present status of bars and spherical detectors, and their prospects for the future, which include dual detectors and spheres with non-resonant transducers. The review covers not only the technical aspects of detectors and the science that will be done, but also analyses the subject in a historic perspective, covering the various detection efforts over four decades, starting from Weber's pioneering work.

abs pdf

Sep 07, 2010

1009.1138 (/preprints)
2010-09-07, 17:20 [edit]


[1009.0765] Constraining the Black Hole Mass Spectrum with LISA Observations II: Direct comparison of detailed models

Authors: Joseph E. Plowman, Ronald W. Hellings, Sachiko Tsuruta

Date: 3 Sep 2010

Abstract: A number of scenarios have been proposed for the origin of the supermassive black holes (SMBHs) that are found in the centres of most galaxies. Many such scenarios predict a high-redshift population of massive black holes (MBHs), with masses in the range 100 to 100000 times that of the Sun. When the Laser Interferometer Space Antenna (LISA) is finally operational, it is likely that it will detect on the order of 100 of these MBH binaries as they merge. The differences between proposed population models produce appreciable effects in the portion of the population which is detectable by LISA, so it is likely that the LISA observations will allow us to place constraints on them. However, gravitational wave detectors such as LISA will not be able to detect all such mergers nor assign precise black hole parameters to the merger, due to weak gravitational wave signal strengths. This paper explores LISA's ability to distinguish between several MBH population models. In this way, we go beyond predicting a LISA observed population and consider the extent to which LISA observations could inform astrophysical modellers. The errors in LISA parameter estimation are applied with a direct method which generates random sample parameters for each source in a population realisation. We consider how the distinguishability varies depending on the choice of source parameters (1 or 2 parameters chosen from masses, redshift or spins) used to characterise the model distributions, with confidence levels determined by 1 and 2-dimensional tests based on the Kolmogorov-Smirnov test.

abs pdf

Sep 07, 2010

1009.0765 (/preprints)
2010-09-07, 17:19 [edit]


[1009.0748] Detection of 16 Gamma-Ray Pulsars Through Blind Frequency Searches Using the Fermi LAT

Authors: The Fermi-LAT Collaboration

Date: 3 Sep 2010

Abstract: Pulsars are rapidly-rotating, highly-magnetized neutron stars emitting radiation across the electromagnetic spectrum. Although there are more than 1800 known radio pulsars, until recently, only seven were observed to pulse in gamma rays and these were all discovered at other wavelengths. The Fermi Large Area Telescope makes it possible to pinpoint neutron stars through their gamma-ray pulsations. We report the detection of 16 gamma-ray pulsars in blind frequency searches using the LAT. Most of these pulsars are coincident with previously unidentified gamma-ray sources, and many are associated with supernova remnants. Direct detection of gamma-ray pulsars enables studies of emission mechanisms, population statistics and the energetics of pulsar wind nebulae and supernova remnants.

abs pdf

Sep 07, 2010

1009.0748 (/preprints)
2010-09-07, 17:18 [edit]


[1009.0608] Bounce hardness index of gravitational waves

Authors: Fumihiko Ishiyama, Ryutaro Takahashi

Date: 3 Sep 2010

Abstract: We present a method of mode analysis to search for signals with frequency evolution and limited duration in data streams of gravitational wave detectors. The frequency precision and time resolution of the frequency evolution with our method are beyond those of Fourier analysis. Applications of this method to the analysis of in-spiral and burst signals show that the signals are characterized by an index which we name "bounce hardness". The index corresponds to the growth rate of the signals.

abs pdf

Sep 05, 2010

1009.0608 (/preprints)
2010-09-05, 23:30 [edit]


[1009.0589] The Initial-Boundary Value Problem in General Relativity

Authors: Oscar Reula, Olivier Sarbach

Date: 3 Sep 2010

Abstract: In this article we summarize what is known about the initial-boundary value problem for general relativity and discuss present problems related to it.

abs pdf

Sep 05, 2010

1009.0589 (/preprints)
2010-09-05, 23:30 [edit]


[1009.0521] Analytic modelling of tidal effects in the relativistic inspiral of binary neutron stars

Authors: Luca Baiotti, Thibault Damour, Bruno Giacomazzo, Alessandro Nagar, Luciano Rezzolla

Date: 2 Sep 2010

Abstract: To detect the gravitational-wave signal from binary neutron stars and extract information about the equation of state of matter at nuclear density, it is necessary to match the signal with a bank of accurate templates. We have performed the longest (to date) general-relativistic simulations of binary neutron stars with different compactnesses and used them to constrain a tidal extension of the effective-one-body model so that it reproduces the numerical waveforms accurately and essentially up to the merger. The typical errors in the phase over the $\simeq 22$ gravitational-wave cycles are $\Delta \phi\simeq \pm 0.24$ rad, thus with relative phase errors $\Delta \phi/\phi \simeq 0.2%$. We also show that with a single choice of parameters, the effective-one-body approach is able to reproduce all of the numerically-computed phase evolutions, in contrast with what found when adopting a tidally corrected post-Newtonian Taylor-T4 expansion.

abs pdf

Sep 02, 2010

1009.0521 (/preprints)
2010-09-02, 23:09 [edit]


[1009.0292] Extreme-Mass-Ratio-Black-Hole-Binary Evolutions with Numerical Relativity

Authors: Carlos O. Lousto, Yosef Zlochower

Date: 1 Sep 2010

Abstract: We perform the first fully nonlinear numerical simulations of black-hole binaries with mass ratios 100:1. Our technique for evolving such extreme mass ratios is based on the moving puncture approach with a new gauge condition and an optimal choice of the mesh refinement (plus large computational resources). We achieve a convergent set of results for simulations starting with a small nonspinning black hole just outside the ISCO that then performs over two orbits before plunging into the 100 times more massive black hole. We compute the gravitational energy and momenta radiated as well as the final remnant parameters and compare these quantities with the corresponding perturbative estimates. The results show a close agreement. We briefly discuss the relevance of this simulations for Advanced LIGO, third-generation ground based detectors, and LISA observations, and self-force computations.

abs pdf

Sep 02, 2010

1009.0292 (/preprints)
2010-09-02, 23:09 [edit]


[1009.0206] Determination of Dark Energy by the Einstein Telescope: Comparing with CMB, BAO and SNIa Observations

Authors: W. Zhao, C. Van Den Broeck, D. Baskaran, B. S. Sathyaprakash

Date: 1 Sep 2010

Abstract: A design study is currently in progress for a third generation gravitational-wave (GW) detector called Einstein Telescope (ET). An important kind of source for ET will be the inspiral and merger of binary neutron stars (BNS) up to $z \sim 2$. If BNS mergers are the progenitors of short-hard $\gamma$-ray bursts, then some fraction of them will be seen both electromagnetically and through GW, so that the luminosity distance and the redshift of the source can be determined separately. An important property of these ‘standard sirens’ is that they are \emph{self-calibrating}: the luminosity distance can be inferred directly from the GW signal, with no need for a cosmic distance ladder. Thus, standard sirens will provide a powerful independent check of the $\Lambda$CDM model. In previous work, estimates were made of how well ET would be able to measure a subset of the cosmological parameters (such as the dark energy parameter $w_0$) it will have access to, assuming that the others had been determined to great accuracy by alternative means. Here we perform a more careful analysis by explicitly using the potential Planck CMB data as prior information for these other parameters. We find that ET will be able to constrain $w_0$ and $w_a$ with accuracies $\Delta w_0 = 0.096$ and $\Delta w_a = 0.296$, respectively. These results are compared with projected accuracies for the JDEM Baryon Acoustic Oscillations (BAO) project and the SNAP Type Ia supernovae (SNIa) observations. Comparing with the combination of the future CMB(Planck)+BAO(JDEM)+SNIa(SNAP) projects, the contribution of GW standard sirens can decrease the uncertainties on $w_0$ and $w_a$ by $\sim 6%$.

abs pdf

Sep 01, 2010

1009.0206 (/preprints)
2010-09-01, 23:32 [edit]


[1009.0157] Radiatively inefficient accretion flows induced by gravitational-wave emission before massive black hole coalescence

Authors: Kimitake Hayasaki (Department Astronomy, Kyoto University)

Date: 1 Sep 2010

Abstract: We study an accretion flow during the gravitational-wave driven evolution of binary massive black holes. After the binary orbit decays due to interacting with a massive circumbinary disk, the binary is decoupled from the circumbinary disk because the orbital-decay timescale due to emission of gravitational wave becomes shorter than the viscous timescale evaluated at the inner edge of circumbinary disk. During the subsequent evolution, the accretion disk, which is truncated at the tidal radius because of the tidal torque, also shrinks as the orbital decay. Assuming that the disk mass changed by this process is all accreted, the whole region of the disk completely becomes radiatively inefficient when the semi-major axis is several hundred Schwarzschild radii. The disk temperature can become comparable with the virial temperature there in spite of a low disk luminosity. The prompt high-energy emission is hence expected long before black hole coalescence as well as the gravitational wave signals. Binary massive black holes finally merge without accretion disks.

abs pdf

Sep 01, 2010

1009.0157 (/preprints)
2010-09-01, 23:32 [edit]


[1009.0018] A Tale of Two Jets

Authors: Nicolas Yunes

Date: 31 Aug 2010

Abstract: One of the most interesting high-energy, astrophysical phenomena are relativistic jets emitted from highly localized sky location. Such jets are common in Nature, observed to high redshift and in a range of wavelengths. Their precise generation mechanism remains a bit of a mystery, but they are generically believed to be powered by black holes. We here summarize the recent simulations of Palenzuela, Lehner and Liebling that shed light on the jet generation mechanism. These authors studied the merger of two non-spinning black holes in the presence of a magnetic field, perpendicular to the orbital plane and anchored by a circumbinary accretion disk, in the "force-free" approximation. They found that each black hole essentially acts as a "straw" that stirs the magnetic field lines around the center of mass as the black holes inspiral. The twisting of the magnetic field lines then generates jets around each black hole, even though these are not spinning. Their simulations show the formation of such a dual jet geometry and how it transitions to a single jet one, as the black holes merge due to gravitational wave emission.

abs pdf

Sep 01, 2010

1009.0018 (/preprints)
2010-09-01, 23:32 [edit]


[1008.5369] Tidal breakup of binary stars at the Galactic Center. II. Hydrodynamic simulations

Authors: Fabio Antonini, James C. Lombardi, David Merritt

Date: 31 Aug 2010

Abstract: In Paper I, we followed the evolution of binary stars as they orbited near the supermassive black hole (SMBH) at the Galactic center, noting the cases in which the two stars would come close enough together to collide. In this paper we replace the point-mass stars by fluid realizations, and use a smoothed-particle hydrodynamics (SPH) code to follow the close interactions. We model the binary components as main-sequence stars with initial masses of 1, 3 and 6 Solar masses, and with chemical composition profiles taken from stellar evolution codes. Outcomes of the close interactions include mergers, collisions that leave both stars intact, and ejection of one star at high velocity accompanied by capture of the other star into a tight orbit around the SMBH. For the first time, we follow the evolution of the collision products for many ($\gtrsim 100$) orbits around the SMBH. Stars that are initially too small to be tidally disrupted by the SMBH can be puffed up by close encounters or collisions, with the result that tidal stripping occurs in subsequent periapse passages. In these cases, mass loss occurs episodically, sometimes for hundreds of orbits before the star is completely disrupted. Repeated tidal flares, of either increasing or decreasing intensity, are a predicted consequence. In collisions involving a low-mass and a high-mass star, the merger product acquires a high core hydrogen abundance from the smaller star, effectively resetting the nuclear evolution "clock" to a younger age. Elements like Li, Be and B that can exist only in the outermost envelope of a star are severely depleted due to envelope ejection during collisions and due to tidal forces from the SMBH. In the absence of collisions, tidal spin-up of stars is only important in a narrow range of periapse distances, $r_t/2\lesssim r_per \lesssim r_t$ with $r_t$ the tidal disruption radius.

abs pdf

Sep 01, 2010

1008.5369 (/preprints)
2010-09-01, 08:40 [edit]


[1008.5280] Bayesian parameter estimation in the second LISA Pathfinder Mock Data Challenge

Authors: M. Nofrarias, C. R&#xf6;ver, M. Hewitson, A. Monsky, G. Heinzel, K. Danzmann, L. Ferraioli, M. Hueller, S. Vitale

Date: 31 Aug 2010

Abstract: A main scientific output of the LISA Pathfinder mission is to provide a noise model that can be extended to the future gravitational wave observatory, LISA. The success of the mission depends thus upon a deep understanding of the instrument, especially the ability to correctly determine the parameters of the underlying noise model. In this work we estimate the parameters of a simplified model of the LISA Technology Package (LTP) instrument. We describe the LTP by means of a closed-loop model that is used to generate the data, both injected signals and noise. Then, parameters are estimated using a Bayesian framework and it is shown that this method reaches the optimal attainable error, the Cramer-Rao bound. We also address an important issue for the mission: how to efficiently combine the results of different experiments to obtain a unique set of parameters describing the instrument.

abs pdf

Sep 01, 2010

1008.5280 (/preprints)
2010-09-01, 08:40 [edit]


[1008.5159] Test bodies and naked singularities: is the self-force the cosmic censor?

Authors: Enrico Barausse, Vitor Cardoso, Gaurav Khanna

Date: 30 Aug 2010

Abstract: It has been suggested by Jacobson and Sotiriou that rotating black holes could be spun-up past the extremal limit by the capture of non-spinning test bodies, which would represent a violation of the Cosmic Censorship Conjecture in four-dimensional, asymptotically flat spacetimes. This analysis, however, neglected radiative and self-force effects. Here we show that for some of the trajectories that can give rise to naked singularities, radiative effects can be neglected. However, for these orbits the conservative part of the self-force is important, and can potentially prevent the appearance of naked singularities.

abs pdf

Sep 01, 2010

1008.5159 (/preprints)
2010-09-01, 08:39 [edit]


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