[1111.6588] The ELM Survey. III. A Successful Targeted Survey for Extremely Low Mass White Dwarfs

Authors: Warren R. Brown (1), Mukremin Kilic (2), Carlos Allende Prieto (3), Scott J. Kenyon (1) ((1) SAO, (2) OU, (3) IAC)

Date: 28 Nov 2011

Abstract: Extremely low mass (ELM) white dwarfs (WDs) with masses <0.25 Msun are rare objects that result from compact binary evolution. Here, we present a targeted spectroscopic survey of ELM WD candidates selected by color. The survey is 71% complete and has uncovered 18 new ELM WDs. Of the 7 ELM WDs with follow-up observations, 6 are short-period binaries and 4 have merger times less than 5 Gyr. The most intriguing object, J1741+6526, likely has either a pulsar companion or a massive WD companion making the system a possible supernova Type Ia or .Ia progenitor. The overall ELM Survey has now identified 19 double degenerate binaries with <10 Gyr merger times. The significant absence of short orbital period ELM WDs at cool temperatures suggests that common envelope evolution creates ELM WDs directly in short period systems. At least one-third of the merging systems are halo objects, thus ELM WD binaries continue to form and merge in both the disk and the halo.

abs pdf

Nov 30, 2011

1111.6588 (/preprints)
2011-11-30, 17:04 [edit]


[1111.6585] The Milky Way has no thick disk

Authors: Jo Bovy (IAS), Hans-Walter Rix (MPIA), David W. Hogg (NYU, MPIA)

Date: 28 Nov 2011

Abstract: Different stellar sub-populations of the Milky Way's stellar disk are known to have different vertical scale heights, their thickness increasing with age. Using SEGUE spectroscopic survey data, we have recently shown that mono-abundance sub-populations, defined in the [\alpha/Fe]-[Fe/H] space, are well described by single exponential spatial-density profiles in both the radial and the vertical direction; therefore any star of a given abundance is clearly associated with a sub-population of scale height h_z. Here, we work out how to determine the stellar surface-mass density contributions at the solar radius R_0 of each such sub-population, accounting for the survey selection function, and for the fraction of the stellar population mass that is reflected in the spectroscopic target stars given populations of different abundances and their presumed age distributions. Taken together, this enables us to derive \Sigma_{R_0}(h_z), the surface-mass contributions of stellar populations with scale height h_z. Surprisingly, we find no hint of a thin-thick disk bi-modality in this mass-weighted scale-height distribution, but a smoothly decreasing function, approximately \Sigma_{R_0}(h_z)\propto \exp(-h_z), from h_z ~ 200 pc to h_z ~ 1 kpc. As h_z is ultimately the structurally defining property of a thin or thick disk, this shows clearly that the Milky Way has a continuous and monotonic distribution of disk thicknesses: there is no 'thick disk' sensibly characterized as a distinct component. We discuss how our result is consistent with evidence for seeming bi-modality in purely geometric disk decompositions, or chemical abundances analyses.

abs pdf

Nov 30, 2011

1111.6585 (/preprints)
2011-11-30, 17:03 [edit]


[1111.6638] The stochastic background from cosmic (super)strings: popcorn and (Gaussian) continuous regimes

Authors: Tania Regimbau, Stefanos Giampanis, Xavier Siemens, Vuk Mandic

Date: 28 Nov 2011

Abstract: In the era of the next generation of gravitational wave experiments a stochastic background from cusps of cosmic (super)strings is expected to be probed and, if not detected, to be significantly constrained. A popcorn-like background can be, for part of the parameter space, as pronounced as the (Gaussian) continuous contribution from unresolved sources that overlap in frequency and time. We study both contributions from unresolved cosmic string cusps over a range of frequencies relevant to ground based interferometers, such as LIGO/Virgo second generation (AdLV) and Einstein Telescope (ET) third generation detectors, the space antenna LISA and Pulsar Timing Arrays (PTA). We compute the sensitivity (at $2 \sigma$ level) in the parameter space for AdLV, ET, LISA and PTA. We conclude that the popcorn regime is complementary to the continuous background. Its detection could therefore enhance confidence in a stochastic background detection and possibly help determine fundamental string parameters such as the string tension and the reconnection probability.

abs pdf

Nov 30, 2011

1111.6638 (/preprints)
2011-11-30, 17:02 [edit]


[1111.6908] Evolution of inspiral orbits around a Schwarzschild black hole

Authors: Niels Warburton, Sarp Akcay, Leor Barack, Jonathan R. Gair, Norichika Sago

Date: 29 Nov 2011

Abstract: We present results from calculations of the orbital evolution in eccentric binaries of nonrotating black holes with extreme mass-ratios. Our inspiral model is based on the method of osculating geodesics, and is the first to incorporate the full gravitational self-force (GSF) effect, including conservative corrections. The GSF information is encapsulated in an analytic interpolation formula based on numerical GSF data for over a thousand sample geodesic orbits. We assess the importance of including conservative GSF corrections in waveform models for gravitational-wave searches.

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Nov 30, 2011

1111.6908 (/preprints)
2011-11-30, 17:02 [edit]


[1111.6607] Tidal interaction in compact binaries: a post-Newtonian affine framework

Authors: V. Ferrari, L. Gualtieri, A. Maselli

Date: 28 Nov 2011

Abstract: We develop a semi-analytical approach, based on the post-Newtonian expansion and on the affine approximation, to model the tidal deformation of neutron stars in the coalescence of black hole-neutron star or neutron star-neutron star binaries. Our equations describe, in a unified framework, both the system orbital evolution, and the neutron star deformations. These are driven by the tidal tensor, which we expand at 1/cˆ3 post-Newtonian order, including spin terms. We test the theoretical framework by simulating black hole-neutron star coalescence up to the onset of mass shedding, which we determine by comparing the shape of the star with the Roche lobe. We validate our approach by comparing our results with those of fully relativistic, numerical simulations.

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Nov 30, 2011

1111.6607 (/preprints)
2011-11-30, 17:01 [edit]


[1111.3742] Origin and Implications of high eccentricities in massive black hole binaries at sub-pc scales

Authors: Constanze Roedig, Alberto Sesana

Date: 16 Nov 2011

Abstract: We outline the eccentricity evolution of sub-parsec massive black hole binaries (MBHBs) forming in galaxy mergers. In both stellar and gaseous environments, MBHBs are expected to grow large orbital eccentricities before they enter the gravitational wave (GW) observational domain. We re--visit the predicted eccentricities detectable by space based laser interferometers (as the proposed ELISA/NGO) for both environments. Close to coalescence, many MBHBs will still maintain detectable eccentricities, spanning a broad range from <10ˆ{-5} up to <~ 0.5. Stellar and gas driven dynamics lead to distinct distributions, with the latter favoring larger eccentricities. At larger binary separations, when emitted GWs will be observed by pulsar timing arrays (PTAs), the expected eccentricities are usually quite large, in the range 0.01-0.7, which poses an important issue for signal modelling and detection algorithms. In this window, large eccentricities also have implications on proposed electromagnetic counterparts to the GW signal, which we briefly review.

abs pdf

Nov 29, 2011

1111.3742 (/preprints)
2011-11-29, 04:48 [edit]


[1111.5819] Bayesian model selection for testing the no-hair theorem with black hole ringdowns

Authors: S. Gossan, J. Veitch, B. S. Sathyaprakash

Date: 24 Nov 2011

Abstract: General relativity predicts that a black hole that results from the merger of two compact stars (either black holes or neutron stars) is initially highly deformed but soon settles down to a quiescent state by emitting a superposition of quasi-normal modes (QNMs). The QNMs are damped sinusoids with characteristic frequencies and decay times that depend only on the mass and spin of the black hole and no other parameter - a statement of the no-hair theorem. In this paper we have examined the extent to which QNMs could be used to test the no-hair theorem with future ground- and space-based gravitational-wave detectors. We model departures from general relativity (GR) by introducing extra parameters which change the mode frequencies or decay times from their general relativistic values. With the aid of numerical simulations and Bayesian model selection, we assess the extent to which the presence of such a parameter could be inferred, and its value estimated. We find that it is harder to decipher the departure of decay times from their GR value than it is with the mode frequencies. Einstein Telescope (ET, a third generation ground-based detector) could detect departures of <1% in the frequency of the dominant QNM mode of a 500 Msun black hole, out to a maximum range of 4 Gpc. In contrast, the New Gravitational Observatory (NGO, an ESA space mission to detect gravitational waves) can detect departures of ~ 0.1% in a 10ˆ8 Msun black hole to a luminosity distance of 30 Gpc (z = 3.5).

abs pdf

Nov 29, 2011

1111.5819 (/preprints)
2011-11-29, 04:47 [edit]


[1111.5650] Estimating the sensitivity of wide-parameter-space searches for gravitational-wave pulsars

Authors: Karl Wette

Date: 23 Nov 2011

Abstract: This paper presents an in-depth study of how to estimate the sensitivity of searches for gravitational-wave pulsars -- rapidly-rotating neutron stars which emit quasi-sinusoidal gravitational waves. It is particularly concerned with searches over a wide range of possible source parameters, such as searches over the entire sky and broad frequency bands. Traditional approaches to estimating the sensitivity of such searches use either computationally-expensive Monte Carlo simulations, or analytic methods which sacrifice accuracy by making an unphysical assumption about the population of sources being searched for. This paper develops a new, analytic method of estimating search sensitivity which does not rely upon this unphysical assumption. Unlike previous analytic methods, the new method accurately predicts the sensitivity obtained using Monte Carlo simulations, while avoiding their computational expense. The change in estimated sensitivity due to properties of the search template bank, and the geographic configuration of the gravitational wave detector network, are also investigated.

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Nov 29, 2011

1111.5650 (/preprints)
2011-11-29, 04:46 [edit]


[1111.5661] Stochastic backgrounds in alternative theories of gravity: overlap reduction functions for pulsar timing arrays

Authors: Sydney J. Chamberlin, Xavier Siemens

Date: 24 Nov 2011

Abstract: In the next decade gravitational waves could be detected using a pulsar timing array. In an effort to develop optimal detection strategies for stochastic backgrounds of gravitational waves in generic metric theories of gravity, we investigate the overlap reduction functions for these theories and discuss their features. We show that sensitivity increases for non-transverse gravitational waves and discuss the physical origin of this effect. We calculate the overlap reduction functions for the current NANOGrav Pulsar Timing Array (PTA) and show that the sensitivity to the vector and scalar-longitudinal modes can increase dramatically for pulsar pairs with small angular separations. For example, the J1853-J1857 pulsar pair, with an angular separation of 3.47 degrees, is about 10ˆ4 times more sensitive to the longitudinal component of the stochastic background, if it's present, than the transverse components.

abs pdf

Nov 29, 2011

1111.5661 (/preprints)
2011-11-29, 04:46 [edit]


[1111.6125] Imprint of the merger and ring-down on the gravitational wave background from black hole binaries coalescence

Authors: S. Marassi, R. Schneider, G. Corvino, V. Ferrari, S. Portegies Zwart

Date: 25 Nov 2011

Abstract: We compute the gravitational wave background (GWB) generated by a cosmological population of (BH-BH) binaries using hybrid waveforms recently produced by numerical simulations of (BH-BH) coalescence, which include the inspiral, merger and ring-down contributions. A large sample of binary systems is simulated using the population synthesis code SeBa, and we extract fundamental statistical information on (BH-BH) physical parameters (primary and secondary BH masses, orbital separations and eccentricities, formation and merger timescales). We then derive the binary birth and merger rates using the theoretical cosmic star formation history obtained from a numerical study which reproduces the available observational data at redshifts $z < 8$. We evaluate the contributions of the inspiral, merger and ring-down signals to the GWB, and discuss how these depend on the parameters which critically affect the number of coalescing (BH-BH) systems. We find that Advanced LIGO/Virgo have a chance to detect the GWB signal from the inspiral phase with a $(S/N)=10$ only for the most optimistic model, which predicts the highest local merger rate of 0.85 Mpc$ˆ{-3}$ Myr$ˆ{-1}$. Third generation detectors, such as ET, could reveal the GWB from the inspiral phase predicted by any of the considered models. In addition, ET could sample the merger phase of the evolution at least for models which predict local merger rates between $[0.053 - 0.85]$ Mpc$ˆ{-3}$ Myr$ˆ{-1}$, which are more than a factor 2 lower the the upper limit inferred from the analysis of the LIGO S5 run\cite{Abadieetal2011}.

abs pdf

Nov 29, 2011

1111.6125 (/preprints)
2011-11-29, 04:43 [edit]


[1106.1616] Measuring neutron-star properties via gravitational waves from binary mergers

Authors: A. Bauswein, H.-Th. Janka (Max Planck Institute for Astrophysics, Garching)

Date: 8 Jun 2011

Abstract: We demonstrate by a large set of merger simulations for symmetric binary neutron stars (NSs) that there is a tight correlation between the frequency peak of the postmerger gravitational-wave (GW) emission and the physical properties of the nuclear equation of state (EoS), e.g. expressed by the radius of the maximum-mass Tolman-Oppenheimer-Volkhoff configuration. Therefore, a single measurement of the peak frequency of the postmerger GW signal will constrain the NS EoS significantly. For plausible optimistic merger-rate estimates a corresponding detection with Advanced LIGO is likely to happen within an operation time of roughly a year.

abs pdf

Nov 23, 2011

1106.1616 (/preprints)
2011-11-23, 23:42 [edit]


[1111.5610] The complete non-spinning effective-one-body metric at linear order in the mass ratio

Authors: Enrico Barausse, Alessandra Buonanno, Alexandre Le Tiec

Date: 23 Nov 2011

Abstract: Using the main result of a companion paper, in which the binding energy of a circular-orbit non-spinning compact binary system is computed at leading-order beyond the test-particle approximation, the exact expression of the effective-one-body (EOB) metric component $gˆ\text{eff}_{tt}$ is obtained through first order in the mass ratio. Combining these results with the recent gravitational self-force calculation of the periastron advance for circular orbits in the Schwarzschild geometry, the EOB metric component $gˆ\text{eff}_{rr}$ is also determined at linear order in the mass ratio. These results assume that the mapping between the real and effective Hamiltonians at the second and third post-Newtonian (PN) orders holds at all PN orders. Our findings also confirm the advantage of resumming the PN dynamics around the test-particle limit if the goal is to obtain a flexible model that can smoothly connect the test-mass and equal-mass limits.

abs pdf

Nov 23, 2011

1111.5610 (/preprints)
2011-11-23, 23:42 [edit]


[1111.5488] Tail terms in gravitational radiation reaction via effective field theory

Authors: S. Foffa, R. Sturani

Date: 23 Nov 2011

Abstract: Gravitational radiation reaction affects the dynamics of gravitationally bound binary systems via "tail" terms which, at the lowest level, modify the conservative dynamics at fourth post-Newtonian order, as it was first computed by Blanchet and Damour. Here we re-produce this result using effective field theory techniques in the framework of the closed-time-path formalism. This tail term is the lowest order example of a short-distance singularity showing up in the conservative dynamics, and it is correctly taken into account within the effective field theory formalism.

abs pdf

Nov 23, 2011

1111.5488 (/preprints)
2011-11-23, 23:41 [edit]


[1111.5609] Gravitational Self-Force Correction to the Binding Energy of Compact Binary Systems

Authors: Alexandre Le Tiec, Enrico Barausse, Alessandra Buonanno

Date: 23 Nov 2011

Abstract: Using the first law of binary black-hole mechanics, we compute the binding energy E and total angular momentum J of two non-spinning compact objects moving on circular orbits with frequency Omega, at leading order beyond the test-particle approximation. By minimizing E(Omega) we recover the exact frequency shift of the Schwarzschild innermost stable circular orbit induced by the conservative piece of the gravitational self-force. Comparing our results for the coordinate invariant relation E(J) to those recently obtained from numerical simulations of comparable-mass non-spinning black-hole binaries, we find a remarkably good agreement, even in the strong-field regime. Our findings confirm that the domain of validity of perturbative calculations may extend well beyond the extreme mass-ratio limit.

abs pdf

Nov 23, 2011

1111.5609 (/preprints)
2011-11-23, 23:41 [edit]


[1111.5378] The First Law of Binary Black Hole Mechanics in General Relativity and Post-Newtonian Theory

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

Date: 23 Nov 2011

Abstract: First laws of black hole mechanics, or thermodynamics, come in a variety of different forms. In this paper, from a purely post-Newtonian (PN) analysis, we obtain a first law for binary systems of point masses moving along an exactly circular orbit. Our calculation is valid through 3PN order and includes, in addition, the contributions of logarithmic terms at 4PN and 5PN orders. This first law of binary point-particle mechanics is then derived from first principles in general relativity, and analogies are drawn with the single and binary black hole cases. Some consequences of the first law are explored for PN spacetimes. As one such consequence, a simple relation between the PN binding energy of the binary system and Detweiler's redshift observable is established. Through it, we are able to determine with high precision the numerical values of some previously unknown high order PN coefficients in the circular-orbit binding energy. Finally, we propose new gauge invariant notions for the energy and angular momentum of a particle in a binary system.

abs pdf

Nov 23, 2011

1111.5378 (/preprints)
2011-11-23, 23:40 [edit]


[1111.5274] Towards a generic test of the strong field dynamics of general relativity using compact binary coalescence: Further investigations

Authors: T. G. F. Li, W. Del Pozzo, S. Vitale, C. Van Den Broeck, M. Agathos, J. Veitch, K. Grover, T. Sidery, R. Sturani, A. Vecchio

Date: 22 Nov 2011

Abstract: Coalescences of binary neutron stars and/or black holes are candidate sources for the first direct detection of gravitational waves. These events will also provide us with the very first empirical access to the genuinely strong-field dynamics of General Relativity (GR). We elaborate on a framework based on Bayesian model selection aimed at detecting deviations from GR, subject to the constraints of Advanced Virgo and LIGO detectors, first introduced by Li et al. (2011). The key aspect of the framework is testing the consistency of the post-Newtonian gravitational-wave phase coefficients in the inspiral regime with the predictions made by GR, without relying on any specific alternative theory of gravity. The framework is suitable for low signal-to-noise events through construction of multiple subtests, most of which involving only a limited number of phase coefficients. The framework also naturally allows for the combination of multiple sources to increase the information extracted for GR testing. In our previous work, we conjectured that this framework can detect generic deviations from GR that can in principle not be accomodated by our model waveforms, on condition that the change in phase near frequencies where the detectors are the most sensitive is comparable to that induced by simple shifts in the lower-order phase coefficients of more than a few percent. To further support this claim, we perform additional numerical experiments in Gaussian and stationary noise according to the expected Advanced LIGO/Virgo noise curves, and injecting signals whose phasing differs structurally from the predictions of GR, but with the magnitude of the deviation still being small. We find that even then, a violation of GR can be established with good confidence.

abs pdf

Nov 23, 2011

1111.5274 (/preprints)
2011-11-23, 23:39 [edit]


[1111.3243] Importance of including small body spin effects in the modelling of intermediate mass-ratio inspirals. II Accurate parameter extraction of strong sources using higher-order spin effects

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

Date: 14 Nov 2011

Abstract: We extend the numerical kludge waveform model introduced in [1] in two ways. We extend the equations of motion for spinning black hole binaries derived by Saijo et al. [2] using spin-orbit and spin-spin couplings taken from perturbative and post-Newtonian (PN) calculations at the highest order available. We also include first-order conservative self-force corrections for spin-orbit and spin-spin couplings, which are derived by comparison to PN results. We generate the inspiral evolution using fluxes that include the most recent calculations of small body spin corrections, spin-spin and spin-orbit couplings and higher-order fits to solutions of the Teukolsky equation. Using a simplified version of this model in [1], we found that small body spin effects may be measured through gravitational wave observations from intermediate-mass ratio inspirals (IMRIs) with mass ratio eta ~ 0.001, when both binary components are rapidly rotating. In this paper we study in detail how the spin of the small/big body affects parameter measurement using a variety of mass and spin combinations for typical IMRIs sources. We find that for IMRI events of a moderately rotating intermediate mass black hole (IMBH) of 10ˆ4 solar masses, and a rapidly rotating central supermassive black hole (SMBH) of 10ˆ6 solar masses, gravitational wave observations made with LISA at a fixed signal-to-noise ratio (SNR) of 1000 will be able to determine the inspiralling IMBH mass, the central SMBH mass, the SMBH spin magnitude, and the IMBH spin magnitude to within fractional errors of ~10ˆ{-3}, 10ˆ{-3}, 10ˆ{-4}, and 9%, respectively. LISA can also determine the location of the source in the sky and the SMBH spin orientation to within ~10ˆ{-4} steradians. We show that by including conservative corrections up to 2.5PN order, systematic errors no longer dominate over statistical errors for IMRIs with typical SNR ~1000.

abs pdf

Nov 22, 2011

1111.3243 (/preprints)
2011-11-22, 15:18 [edit]


[1111.3044] Effect of calibration errors on Bayesian parameter estimation for gravitational wave signals from inspiral binary systems in the Advanced Detectors era

Authors: Salvatore Vitale, Walter Del Pozzo, Tjonnie G. F. Li, Chris Van Den Broeck, Ilya Mandel, Ben Aylott, John Veitch

Date: 13 Nov 2011

Abstract: By 2015 the advanced versions of the gravitational-wave detectors Virgo and LIGO will be online. They will collect data in coincidence with enough sensitivity to potentially deliver multiple detections of gravitation waves from inspirals of compact-object binaries. This work is focused on understanding the effects introduced by uncertainties in the calibration of the interferometers. We consider plausible calibration errors based on estimates obtained during LIGO's fifth and Virgo's third science runs, which include frequency-dependent amplitude errors of $\sim 10%$ and frequency-dependent phase errors of $\sim 3$ degrees in each instrument. We quantify the consequences of such errors estimating the parameters of inspiraling binaries. We find that the systematics introduced by calibration errors on the inferred values of the chirp mass and mass ratio are smaller than 20% of the statistical measurement uncertainties in parameter estimation for 90% of signals in our mock catalog. Meanwhile, the calibration-induced systematics in the inferred sky location of the signal are smaller than $\sim 50%$ of the statistical uncertainty. We thus conclude that calibration-induced errors at this level are not a significant detriment to accurate parameter estimation.

abs pdf

Nov 22, 2011

1111.3044 (/preprints)
2011-11-22, 15:17 [edit]


[1111.3055] Eccentric black hole-neutron star mergers: effects of black hole spin and equation of state

Authors: William E. East, Frans Pretorius, Branson C. Stephens

Date: 13 Nov 2011

Abstract: There is a high level of interest in black hole-neutron star binaries, not only because their mergers may be detected by gravitational wave observatories in the coming years, but also because of the possibility that they could explain a class of short duration gamma-ray bursts. We study black hole-neutron star mergers that occur with high eccentricity as may arise from dynamical capture in dense stellar regions such as nuclear or globular clusters. We perform general relativistic simulations of binaries with a range of impact parameters, three different initial black hole spins (zero, aligned and anti-aligned with the orbital angular momentum), and neutron stars with three different equations of state. We find a rich diversity across these parameters in the resulting gravitational wave signals and matter dynamics, which should also be reflected in the consequent electromagnetic emission. Before tidal disruption, the gravitational wave emission is significantly larger than perturbative predictions suggest for periapsis distances close to effective innermost stable separations, exhibiting features reflecting the zoom-whirl dynamics of the orbit there. Guided by the simulations, we develop a simple model for the change in orbital parameters of the binary during close encounters. Depending upon the initial parameters of the system, we find that mass transfer during non-merging close encounters can range from essentially zero to a sizable fraction of the initial neutron star mass. The same holds for the amount of material outside the black hole post-merger, and in some cases roughly half of this material is estimated to be unbound. We also see that non-merging close encounters generically excite large oscillations in the neutron star that are qualitatively consistent with f-modes.

abs pdf

Nov 22, 2011

1111.3055 (/preprints)
2011-11-22, 15:17 [edit]


[1111.4009] Cosmic Black-Hole Hair Growth and Quasar OJ287

Authors: M. W. Horbatsch, C. P. Burgess

Date: 17 Nov 2011

Abstract: An old result ({\tt astro-ph/9905303}) by Jacobson implies that a black hole with Schwarzschild radius $r_s$ acquires scalar hair, $Q \propto r_sˆ2 \mu$, when the (canonically normalized) scalar field in question is slowly time-dependent far from the black hole, $\partial_t \phi \simeq \mu M_p$ with $\mu r_s \ll 1$ time-independent. Such a time dependence could arise in scalar-tensor theories either from cosmological evolution, or due to the slow motion of the black hole within an asymptotic spatial gradient in the scalar field. Most remarkably, the amount of scalar hair so induced is independent of the strength with which the scalar couples to matter. We argue that Jacobson's Miracle Hair-Growth Formula${}ˆ\copyright$ implies, in particular, that an orbiting pair of black holes can radiate {\em dipole} radiation, provided only that the two black holes have different masses. Quasar OJ 287, situated at redshift $z \simeq 0.306$, has been argued to be a double black-hole binary system of this type, whose orbital decay recently has been indirectly measured and found to agree with the predictions of General Relativity to within 6%. We argue that the absence of observable scalar dipole radiation in this system yields the remarkable bound $|\,\mu| < (16 \, \hbox{days})ˆ{-1}$ on the instantaneous time derivative at this redshift (as opposed to constraining an average field difference, $\Delta \phi$, over cosmological times), provided only that the scalar is light enough to be radiated — i.e. $m \lsim 10ˆ{-23}$ eV — independent of how the scalar couples to matter. This can also be interpreted as constraining (in a more model-dependent way) the binary's motion relative to any spatial variation of the scalar field within its immediate vicinity within its host galaxy.

abs pdf

Nov 22, 2011

1111.4009 (/preprints)
2011-11-22, 15:15 [edit]


[1111.4014] Gravitational Waves from Global Second Order Phase Transitions

Authors: John T. Giblin Jr, Larry R. Price, Xavier Siemens, Brian Vlcek

Date: 17 Nov 2011

Abstract: Global second-order phase transitions are expected to produce scale-invariant gravitational wave spectra. In this manuscript we explore the dynamics of a symmetry-breaking phase transition using lattice simulations. We explicitly calculate the stochastic gravitational wave background produced during the transition and subsequent self-ordering phase. We comment on this signal as it compares to the scale-invariant spectrum produced during inflation.

abs pdf

Nov 22, 2011

1111.4014 (/preprints)
2011-11-22, 15:15 [edit]


[1111.4516] The Critical Coupling Likelihood Method: A new approach for seamless integration of environmental and operating conditions of gravitational wave detectors into gravitational wave searches

Authors: Cesar A. Costa, Cristina V. Torres

Date: 18 Nov 2011

Abstract: As part of the current LIGO search for gravitational waves (GWs) we find ourselves trying to determine if and when noise is coupling into the instrument. The Critical Coupling Likelihood (CCL) method has been developed to directly fold information about the potential influence of instrument noise sources into GW search efforts. By using the CCL functions of uncoupled (background) and coupled (foreground) instrumental noise sources, CCL should be able to identify undesirable coupled instrumental noise from potential GW candidates. Our preliminary results show that CCL can associate up to ~80% of observed artifacts with SNR>=8, to local noise sources. That reduces the duty cycle of the instrument by less than 15%. An approach like CCL will become increasingly important as we move into the Advanced LIGO era, going from a first GW detection to gravitational wave astronomy.

abs pdf

Nov 22, 2011

1111.4516 (/preprints)
2011-11-22, 15:12 [edit]


[1111.3737] Analytical meets numerical relativity - status of complete gravitational waveform models

Authors: Frank Ohme

Date: 16 Nov 2011

Abstract: Models of gravitational waveforms from coalescing black-hole binaries play a crucial role in the efforts to detect and interpret those signatures in the data of large-scale interferometers. Here we summarize recent models that combine information both from analytical approximations and numerical relativity. We briefly lay out and compare the strategies employed to build such complete models and we recapitulate the errors associated with various aspects of the modelling process.

abs pdf

Nov 21, 2011

1111.3737 (/preprints)
2011-11-21, 19:05 [edit]


[1111.3484] The 2005 - 2010 multiwavelength campaign of OJ287

Authors: Mauri Valtonen, Aimo Sillanp&#xe4;&#xe4;

Date: 15 Nov 2011

Abstract: The light curve of quasar OJ287 extends from 1891 up today without major gaps. This is partly due to extensive studies of historical plate archives by Rene Hudec and associates, and partly due to several observing campaigns in recent times. Here we summarize the results of the 2005 - 2010 observing campaign, in which several hundred scientists and amateur astronomers took part. The main results are the following: (1) The 2005 October optical outburst came at the expected time, thus confirming the General Relativistic precession in the binary black hole system. At the same time, this result disproved the model of a single black hole system with accretion disk oscillations, as well as several toy models of binaries without relativistic precession. (2) The nature of the radiation of the 2005 October outburst was expected to be bremsstrahlung from hot gas at a temperature of 3 10ˆ5 degrees K. This was confirmed by combined ground based and ultraviolet observations using the XMM-Newton X-ray telescope. (3) A secondary outburst of the same nature was expected at 2007 September 13. Within the accuracy of the observations (about 6 hours), it started at the correct time. Due to the bremsstrahlung nature of the outburst, the radiation was unpolarized, as expected. (4) Further synchrotron outbursts were expected following the two bremsstrahlung outbursts. They came as scheduled between 2007 October and 2009 December. (5) Due to the effect of the secondary on the overall direction of the jet, the parsec scale jet is expected to rotate in the sky by a large angle, which has been confirmed. The OJ287 binary black hole system is currently our best laboratory for testing theories of gravitation. Using OJ287, the correctness of General Relativity has now been demonstrated up to the second Post-Newtonian order, higher than has been possible using binary pulsars.

abs pdf

Nov 21, 2011

1111.3484 (/preprints)
2011-11-21, 19:05 [edit]


[1111.3621] Performance of a Chirplet-based analysis for gravitational waves from binary black hole mergers

Authors: Satya Mohapatra, Zachary Nemtzow, Eric Chassande-Mottin, Laura Cadonati

Date: 15 Nov 2011

Abstract: The gravitational wave (GW) signature of a binary black hole (BBH) coalescence is characterized by rapid frequency evolution in the late inspiral and merger phases. For a system with total mass larger than 100 M_sun, ground based GW detectors are sensitive to the merger phase, and the in-band whitened waveform is a short-duration transient lasting about 10-30 ms. For a symmetric mass system with total mass between 10 and 100 M_sun, the detector is sensitive instead to the inspiral phase and the in-band signal has a longer duration, between 30 ms - 3 s. Omega is a search algorithm for GW bursts that, with the assumption of locally stationary frequency evolution, uses sine-Gaussian wavelets as a template bank to decompose interferometer strain data. The local stationarity of sine-Gaussians induces a performance loss for the detection of lower mass BBH signatures, due to the mismatch between template and signal. We present the performance of a modified version of the Omega algorithm, Chirplet Omega, which allows a linear variation of frequency, to target BBH coalescences. The use of Chirplet-like templates enhances the measured signal-to-noise ratio due to less mismatch between template and data, and increases the detectability of lower mass BBH coalescences. We present the results of a performance study of Chirplet Omega in colored Gaussian noise at initial LIGO sensitivity.

abs pdf

Nov 17, 2011

1111.3621 (/preprints)
2011-11-17, 08:02 [edit]


[1111.3605] Resonances in Extreme Mass-Ratio Inspirals: Asymptotic and Hyperasymptotic Analysis

Authors: Jonathan R Gair, Nicolas Yunes, Carl M Bender

Date: 15 Nov 2011

Abstract: An expected source of gravitational waves for future detectors in space are the inspirals of small compact objects into much more massive black holes. These sources have the potential to provide a wealth of information about astronomy and fundamental physics. On short timescales the orbit of the small object is approximately geodesic. Generic geodesics for a Kerr black hole spacetime have a complete set of integrals and can be characterized by three frequencies of the motion. Over the course of an inspiral, a typical system will pass through resonances where two of these frequencies become commensurate. The effect of the resonance will be to alter significantly the rate of inspiral for the duration of the resonance. Understanding the impact of these resonances on gravitational wave phasing is important to detect and exploit these signals for astrophysics and fundamental physics. Two differential equations that might describe the passage of an inspiral through such a resonance are investigated. These differ depending on whether it is the phase or the frequency components of a Fourier expansion of the motion that are taken to be continuous through the resonance. Asymptotic and hyperasymptotic analysis are used to find the late-time analytic behavior of the solution for a system that has passed through a resonance. Linearly growing (weak resonances) or linearly decaying (strong resonances) solutions are found depending on the strength of the resonance. In the weak-resonance case, frequency resonances leave an imprint (a resonant memory) on the gravitational frequency evolution. The transition between weak and strong resonances is characterized by a square-root singularity, and as one approaches this transition from above, the solutions to the frequency resonance equation bunch up into families exponentially fast.

abs pdf

Nov 17, 2011

1111.3605 (/preprints)
2011-11-17, 08:02 [edit]


[1111.2655] Superconducting Antenna Concept for Gravitational Wave Radiation

Authors: A. Gulian, J. Foreman, V. Nikoghosyan, S. Nussinov, L. Sica, J. Tollaksen

Date: 11 Nov 2011

Abstract: A new concept for detectors of gravitational wave radiation is discussed. Estimates of its sensitivity suggest that these devices will be able to detect gravitational waves with amplitudes as low as h0~10-26. Such sensitivity could be obtained at spatial scales as small as 10 meters. Devices based on this concept require operational temperatures below the critical temperatures of their superconducting components.

abs pdf

Nov 14, 2011

1111.2655 (/preprints)
2011-11-14, 08:28 [edit]


[1111.2816] Cosmological distance indicators by coalescing binaries

Authors: Mariafelicia De Laurentis, Salvatore Capozziello, Ivan De Martino, Michelangelo Formisano

Date: 11 Nov 2011

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.

abs pdf

Nov 14, 2011

1111.2816 (/preprints)
2011-11-14, 08:27 [edit]


[1111.0005] Towards improving the prospects for coordinated gravitational-wave and electromagnetic observations

Authors: Ilya Mandel, Luke Z. Kelley, Enrico Ramirez-Ruiz

Date: 31 Oct 2011

Abstract: We discuss two approaches to searches for gravitational-wave (GW) and electromagnetic (EM) counterparts of binary neutron star mergers. The first approach relies on triggering archival searches of GW detector data based on detections of EM transients. We introduce a quantitative approach to evaluate the improvement to GW detector reach due to the extra information gained from the EM transient and the increased confidence in the presence of a signal from a binary merger. We also advocate utilizing other transients in addition to short gamma ray bursts. The second approach involves following up GW candidates with targeted EM observations. We argue for the use of slower but optimal parameter-estimation techniques to localize the source on the sky, and for a more sophisticated use of astrophysical prior information, including galaxy catalogs, to find preferred followup locations.

abs pdf

Nov 14, 2011

1111.0005 (/preprints)
2011-11-14, 08:27 [edit]


[1111.2701] The 2.5PN linear momentum flux and associated recoil from inspiralling compact binaries in quasi-circular orbits: Nonspinning case

Authors: Chandra Kant Mishra (RRI & IISc, India), K. G. Arun (CMI, India), Bala R. Iyer (RRI, India)

Date: 11 Nov 2011

Abstract: Anisotropic emission of gravitational-waves (GWs) from inspiralling compact binaries leads to the loss of linear momentum and hence gravitational recoil of the system. The loss rate of linear momentum in the far-zone of the source (a nonspinning binary system of black holes in quasi-circular orbit) is investigated at the 2.5 post-Newtonian (PN) order and used to provide an analytical expression in harmonic coordinates for the 2.5PN accurate recoil velocity of the binary accumulated in the inspiral phase. The maximum recoil velocity of the binary system at the end of its inspiral phase (i.e at the innermost stable circular orbit (ISCO)) estimated by the 2.5PN formula is of the order of 4 km/s which is smaller than the 2PN estimate of 22 km/s and indicates the importance of higher order post-Newtonian (PN) corrections. Going beyond inspiral, we also provide an estimate of the more important contribution to the recoil velocity from the plunge phase. The maximum recoil velocity at the end of the plunge, involving contributions both from inspiral and plunge phase, for a binary with symmetric mass ratio $\nu=0.2$ is of the order of 182 km/s.

abs pdf

Nov 14, 2011

1111.2701 (/preprints)
2011-11-14, 08:27 [edit]


[1111.1677] Black hole-neutron star mergers for 10 solar mass black holes

Authors: Francois Foucart, Matthew D. Duez, Lawrence E. Kidder, Mark A. Scheel, Bela Szilagyi, Saul A. Teukolsky

Date: 7 Nov 2011

Abstract: General relativistic simulations of black hole-neutron star mergers have currently been limited to low-mass black holes (less than 7 solar mass), even though population synthesis models indicate that a majority of mergers might involve more massive black holes (10 solar mass or more). We present the first general relativistic simulations of black hole-neutron star mergers with 10 solar mass black holes. For massive black holes, the tidal forces acting on the neutron star are usually too weak to disrupt the star before it reaches the innermost stable circular orbit of the black hole. Varying the spin of the black hole in the range a/M = 0.5-0.9, we find that mergers result in the disruption of the star and the formation of a massive accretion disk only for large spins a/M>0.7-0.9. From these results, we obtain updated constraints on the ability of BHNS mergers to be the progenitors of short gamma-ray bursts as a function of the mass and spin of the black hole. We also discuss the dependence of the gravitational wave signal on the black hole parameters, and provide waveforms and spectra from simulations beginning 7-8 orbits before merger.

abs pdf

Nov 14, 2011

1111.1677 (/preprints)
2011-11-14, 08:27 [edit]


[1111.2802] Jets from Tidal Disruptions of Stars by Black Holes

Authors: Julian H. Krolik, Tsvi Piran

Date: 11 Nov 2011

Abstract: Tidal disruption of main sequence stars by black holes has generally been thought to lead to a signal dominated by UV emission. If, however, the black hole spins rapidly and the poloidal magnetic field intensity on the black hole horizon is comparable to the inner accretion disk pressure, a powerful jet may form whose luminosity can easily exceed the thermal UV luminosity. When the jet beam points at Earth, its non-thermal luminosity can dominate the emitted spectrum. The thermal and non-thermal components decay differently with time. In particular, the thermal emission should remain roughly constant for a significant time after the period of maximum accretion, beginning to diminish only after a delay, whereas after the peak accretion rate, the non-thermal jet emission decays, but then reaches a plateau. When the newly-found flare source Swift J2058 is analyzed in terms of this model, it is found to be consistent with an event in which a main sequence solar-type star is disrupted by a black hole of mass at least $\sim 10ˆ7 M_{\odot}$. Swift may have already observed the beginning of the flat phase in the non-thermal emission from this source. Optical photometry over the first $\simeq 40$ d of this flare is also consistent with this picture, but there is a large uncertainty in the bolometric correction. We suggest that future searches for main sequence tidal disruptions use methods sensitive to jet radiation as well as to thermal UV radiation.

abs pdf

Nov 14, 2011

1111.2802 (/preprints)
2011-11-14, 08:27 [edit]


[1111.1383] The speed of gravitational wave: could larger than the speed of light

Authors: Xin Li, Zhe Chang

Date: 6 Nov 2011

Abstract: By making use of the weak gravitational field approximation, we obtain the linearized solution of the gravitational vacuum field equation in Finsler spacetime. The plane-waves solution and dispersion relation of gravitational wave in Finsler spacetime is given. It implies that the speed of gravitational wave could larger than the speed of light. It is compatible with the very recent results of OPERA collaboration, which found that the speed of neutrinos is faster than the speed of light. The wave vector of gravitational wave is null in Finsler spacetime, it would not lose energy via gravitational Cherenkov radiation. The results of OPERA collaboration hint that spacetime may be Finslerian.

abs pdf

Nov 14, 2011

1111.1383 (/preprints)
2011-11-14, 08:27 [edit]


[1111.2576] A Geostationary Gravitational Wave Interferometer (GEOGRAWI)

Authors: Massimo Tinto, J. C. N. de Araujo, Odylio D. Aguiar, Eduardo da Silva Alves

Date: 10 Nov 2011

Abstract: We propose a Geostationary Gravitational Wave Interferometer (GEOGRAWI) mission concept for making observations in the sub-Hertz band. GEOGRAWI is expected to meet some of LISA's science goals in the lower part of its accessible frequency band ($10ˆ{-4} - 2 \times 10ˆ{-2}$ Hz), and to outperform them by a large margin in the higher-part of it ($2 \times 10ˆ{-2} - 10$ Hz). As a consequence of its Earth-bound orbit, GEOGRAWI is significantly less expensive than the interplanetary LISA mission and could be either an entirely US mission or managed and operated by NASA in partnership with the Brazilian Space Agency.

abs pdf

Nov 11, 2011

1111.2576 (/preprints)
2011-11-11, 23:42 [edit]


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