## [1207.7176] Einstein@Home all-sky search for periodic gravitational waves in LIGO S5 data

Date: 31 Jul 2012

Abstract: This paper presents results of an all-sky searches for periodic gravitational waves in the frequency range [50, 1190] Hz and with frequency derivative ranges of [-2 \times 10ˆ-9, 1.1 \times 10ˆ-10] Hz/s for the fifth LIGO science run (S5). The novelty of the search lies in the use of a non-coherent technique based on the Hough-transform to combine the information from coherent searches on timescales of about one day. Because these searches are very computationally intensive, they have been deployed on the Einstein@Home distributed computing project infrastructure. The search presented here is about a factor 3 more sensitive than the previous Einstein@Home search in early S5 LIGO data. The post-processing has left us with eight surviving candidates. We show that deeper follow-up studies rule each of them out. Hence, since no statistically significant gravitational wave signals have been detected, we report upper limits on the intrinsic gravitational wave amplitude h0. For example, in the 0.5 Hz-wide band at 152.5 Hz, we can exclude the presence of signals with h0 greater than 7.6 \times 10ˆ-25 with a 90% confidence level.

#### Jul 31, 2012

1207.7176 (/preprints)
2012-07-31, 20:57 

## [1207.6961] Aligned Spins: Orbital Elements, Decaying Orbits, and Last Stable Circular Orbit to high post-Newtonian Orders

Authors: Manuel Tessmer, Johannes Hartung, Gerhard Sch&#xe4;fer

Date: 30 Jul 2012

Abstract: In this article the quasi-Keplerian parameterisation for the case that spins and orbital angular momentum in a compact binary system are aligned or anti-aligned with the orbital angular momentum vector is extended to 3PN point-mass, next-to-next-to-leading order spin-orbit, next-to-next-to-leading order spin(1)-spin(2), and next-to-leading order spin-squared dynamics in the conservative regime. In a further step, we use the expressions for the radiative multipole moments with spin to leading order linear and quadratic in both spins to compute radiation losses of the orbital binding energy and angular momentum. Orbital averaged expressions for the decay of energy and eccentricity are provided. An expression for the last stable circular orbit is given in terms of the angular velocity type variable $x$.

#### Jul 30, 2012

1207.6961 (/preprints)
2012-07-30, 20:47 

## [1207.6755] Galactic Center Research: Manifestations of the Central Black Hole

Authors: Mark Morris, Leo Meyer, Andrea Ghez

Date: 29 Jul 2012

Abstract: This review summarizes a few of the frontiers of Galactic center research that are currently the focus of considerable activity and attention. It is aimed at providing a necessarily incomplete sketch of some of the timely work being done on phenomena taking place in, or originating in, the central few parsecs of the Galaxy, with particular attention to topics related to the Galactic black hole (GBH). We have chosen to expand on the following exciting topics: 1) the characterization and the implications for the variability of emission from the GBH, 2) the strong evidence for a powerful X-ray flare in the Galactic center within the past few hundred years, and the likelihood that the GBH is implicated in that event, 3) the prospects for detecting the "shadow" of the GBH, 4) an overview of the current state of research on the central S-star cluster, and what has been learned from the stellar orbits within that cluster, and 5) the current hypotheses for the origin of the G2 dust cloud that is projected to make a close passage by the GBH in 2013.

#### Jul 30, 2012

1207.6755 (/preprints)
2012-07-30, 20:46 

## [1207.6406] Detecting binary neutron star systems with spin in advanced gravitational-wave detectors

Authors: Duncan A. Brown, Ian Harry, Andrew Lundgren, Alexander H. Nitz

Date: 26 Jul 2012

Abstract: The detection of gravitational waves from binary neutron stars is a major goal of the gravitational-wave observatories Advanced LIGO and Advanced Virgo. Previous searches for binary neutron stars with LIGO and Virgo neglected the component stars' angular momentum (spin). We demonstrate that neglecting spin in matched-filter searches causes advanced detectors to lose more than 3% of the possible signal-to-noise ratio for 59% (6%) of sources, assuming that neutron star dimensionless spins, $cJ/GMˆ2$, are uniformly distributed with magnitudes between 0 and 0.4 (0.05) and that the neutron stars have isotropically distributed spin orientations. We present a new method of constructing filter banks for advanced-detector searches, which can create template banks of signals with non-zero spins that are (anti-)aligned with the orbital angular momentum. We show that this search loses more than 3% of the maximium signal-to-noise for only 9% (0.2%) of BNS sources with dimensionless spins between 0 and 0.4 (0.05) and isotropic spin orientations. Use of this template bank will prevent selection bias in gravitational-wave searches and allow a more accurate exploration of the distribution of spins in binary neutron stars.

#### Jul 29, 2012

1207.6406 (/preprints)
2012-07-29, 23:25 

## [1207.6401] Black-Hole Spin Dependence in the Light Curves of Tidal Disruption Events

Authors: Michael Kesden

Date: 26 Jul 2012

Abstract: A star orbiting a supermassive black hole can be tidally disrupted if the black hole's gravitational tidal field exceeds the star's self gravity at pericenter. Some of stellar tidal debris can become gravitationally bound to the black hole and be subsequently accreted, leading to a bright electromagnetic flare. In the Newtonian limit, this flare will have a light curve that scales as tˆ-5/3 if the tidal debris has a flat distribution in binding energy. We investigate the time dependence of the black-hole mass accretion rate when tidal disruption occurs close enough the black hole that relativistic effects are significant. We find that for orbits with pericenters comparable to the radius of the marginally bound circular orbit, relativistic effects can double the peak accretion rate and halve the time it takes to reach this peak accretion rate. The accretion rate depends on both the magnitude of the black-hole spin and its orientation with respect to the stellar orbit; for orbits with a given pericenter radius in Boyer-Lindquist coordinates, a maximal black-hole spin anti-aligned with the orbital angular momentum leads to the largest peak accretion rate.

#### Jul 29, 2012

1207.6401 (/preprints)
2012-07-29, 23:25 

## [1207.5595] EMRI corrections to the angular velocity and redshift factor of a mass in circular orbit about a Kerr black hole

Authors: Abhay G. Shah, John L. Friedman, Tobias S. Keidl

Date: 24 Jul 2012

Abstract: This is the first of two papers on computing the self-force in a radiation gauge for a particle moving in circular, equatorial orbit about a Kerr black hole. In the EMRI (extreme-mass-ratio inspiral) framework, with mode-sum renormalization, we compute the renormalized value of the quantity $h_{\alpha\beta}uˆ\alpha uˆ\beta$, gauge-invariant under gauge transformations generated by a helically symmetric gauge vector; and we find the related order $\frak{m}$ correction to the particle's angular velocity at fixed renormalized redshift (and to its redshift at fixed angular velocity). The radiative part of the perturbed metric is constructed from the Hertz potential which is extracted from the Weyl scalar by an algebraic inversion\cite{sf2}. We then write the spin-weighted spheroidal harmonics as a sum over spin-weighted spherical harmonics and use mode-sum renormalization to find the renormalization coefficients by matching a series in $L=\ell+½$ to the large-$L$ behavior of the expression for $H := \frac12 h_{\alpha\beta}uˆ\alpha uˆ\beta$. The non-radiative parts of the perturbed metric associated with changes in mass and angular momentum are calculated in the Kerr gauge.

#### Jul 28, 2012

1207.5595 (/preprints)
2012-07-28, 09:44 

## [1207.5645] Observing the dynamics of super-massive black hole binaries with Pulsar Timing Arrays

Authors: C. M. F. Mingarelli, K. Grover, T. Sidery, R. J. E. Smith, A. Vecchio

Date: 24 Jul 2012

Abstract: Pulsar Timing Arrays are a prime tool to study unexplored astrophysical regimes with gravitational waves. Here we show that the detection of gravitational radiation from individually resolvable super-massive black hole binary systems can yield direct information about the masses and spins of the black holes, provided that the gravitational-wave induced timing fluctuations both at the pulsar and at the Earth are detected. This in turn provides a map of the non-linear dynamics of the gravitational field and a new avenue to tackle open problems in astrophysics connected to the formation and evolution of super-massive black holes. We discuss the potential, the challenges and the limitations of these observations.

#### Jul 28, 2012

1207.5645 (/preprints)
2012-07-28, 09:44 

## [1207.6304] Black Hole-Neutron Star Mergers: Disk Mass Predictions

Authors: Francois Foucart

Date: 26 Jul 2012

Abstract: Determining the final result of black hole-neutron star mergers, and in particular the amount of matter remaining outside the black hole at late times, has been one of the main motivations behind the numerical simulation of these systems. Black hole-neutron star binaries are amongst the most likely progenitors of short gamma-ray bursts — as long as they result in the formation of massive (at least ~0.1 solar mass) accretion disks around the black hole. Whether this actually happens strongly depends on the physical characteristics of the system, and in particular on the mass ratio, the spin of the black hole, and the radius of the neutron star. We present here a simple two-parameter model, fitted to existing numerical results, for the determination of the mass remaining outside the black hole a few milliseconds after a black hole-neutron star merger. This model predicts the remnant mass within a few percents of the mass of the neutron star, at least for remnant masses up to 20% of the neutron star mass. Results across the range of parameters deemed to be the most likely astrophysically are presented here. We find that, for 10 solar mass black holes, massive disks are only possible for fairly large neutron stars (R>12km), or quasi-extremal black hole spins (a/M>0.9). We also use our model to discuss how the equation of state of the neutron star affects the final remnant, and the strong influence that this can have on the rate of short gamma-ray bursts produced by black hole-neutron star mergers.

#### Jul 26, 2012

1207.6304 (/preprints)
2012-07-26, 23:38 

## [1207.5410] Testing gravitational theories using Eccentric Eclipsing Detached Binaries

Authors: Mariafelicia De Laurentis, Rosario De Rosa, Fabio Garufi, Leopoldo Milano

Date: 23 Jul 2012

Abstract: In this paper we compare the effects of different theories of gravitation on the apsidal motion of a sample of Eccentric Eclipsing Detached Binary stars. The comparison is performed by using the formalism of the Post-Newtonian parametrization to calculate the theoretical advance at periastron and compare it to the observed one, after having considered the effects of the structure and rotation of the involved stars. A variance analysis on the results of this comparison, shows that no significant difference can be found due to the effect of the different theories under test with respect to the standard General Relativity. It will be possible to observe differences, as we would expect, by checking the observed period variation on a much larger lapse of time. It can also be noticed from our results, that f(R) theory is the nearest to GR with respect to the other tested theories.

#### Jul 23, 2012

1207.5410 (/preprints)
2012-07-23, 23:09 

## [1207.5359] Gravitational wave energy spectrum of hyperbolic encounters

Authors: Lorenzo De Vittori, Philippe Jetzer, Antoine Klein

Date: 23 Jul 2012

Abstract: The emission of gravitational waves is studied for a system of massive objects interacting on hyperbolic orbits within the quadrupole approximation following the work of Capozziello et al. Here we focus on the derivation of an analytic formula for the energy spectrum of the emitted waves. We checked numerically that our formula is in agreement with the two limiting cases for which results were already available: for the eccentricity {\epsilon} = 1, the parabolic case whose spectrum was computed by Berry and Gair, and the large {\epsilon} limit with the formula given by Turner.

#### Jul 23, 2012

1207.5359 (/preprints)
2012-07-23, 23:09 

## [1207.5448] Towards the 4th post-Newtonian Hamiltonian for two-point-mass systems

Authors: Piotr Jaranowski, Gerhard Sch&#xe4;fer

Date: 23 Jul 2012

Abstract: The article presents the conservative dynamics of gravitationally interacting two-point-mass systems up to the eight order in the inverse power of the velocity of light, i.e.\ 4th post-Newtonian (4PN) order, and up to quadratic order in Newton's gravitational constant. Additionally, all logarithmic terms at the 4PN order are given as well as terms describing the test-mass limit. With the aid of the Poincaré algebra additional terms are obtained. The dynamics is presented in form of an autonomous Hamiltonian derived within the formalism of Arnowitt, Deser and Misner. Out of the 57 different terms of the 4PN Hamiltonian in the center-of-mass frame, the coefficients of 45 of them are derived. Reduction of the obtained results to circular orbits is performed resulting in the 4PN-accurate formula for energy expressed in terms of angular frequency in which two coefficients are obtained for the first time.

#### Jul 23, 2012

1207.5448 (/preprints)
2012-07-23, 23:08 

## [1207.3361] Systematic errors in measuring parameters of non-spinning compact binary coalescences with post-Newtonian templates

Authors: Sukanta Bose, Shaon Ghosh, Ajith Parameswaran

Date: 13 Jul 2012

Abstract: We study the astrophysical impact of inaccurate and incomplete modeling of the gravitational waveforms from compact binary coalescences (CBCs). We do so by the matched filtering of complete inspiral-merger-ringdown (IMR) signals with a bank of inspiral-phase templates modeled after the 3.5 post-Newtonian TaylorT1 approximant. The rationale for the choice of the templates is threefold: (1) The inspiral phase of the Phenomenological signals, which are an example of complete IMR signals, is modeled on the same TaylorT1 approximant. (2) In the low-mass limit, where the merger and ringdown phases last much shorter than the inspiral phase, the errors should tend to vanishingly small values and, thus, provide an important check on the numerical aspects of our simulations. (3) Since the binary black hole (BBH) signals are not yet known for mass-ratios above ten and since signals from CBCs involving neutron stars are affected by uncertainties in the knowledge of their equation of state, inspiral templates are still in use in searches for those signals. The results from our numerical simulations are compared with analytical calculations of the systematic errors using the Fisher matrix on the template parameter space. We find that the loss in signal-to-noise ratio (SNR) can be as large as 60% even for binary black holes with component masses m1 = 13M\odot and m2 = 20M\odot. Also, the estimated total-mass for the same pair can be off by as much as 20%. Both of these are worse for some higher-mass combinations. Even the estimation of the symmetric mass-ratio {\eta} suffers a nearly 20% error for this example, and can be worse than 50% for the mass ranges studied here. These errors significantly dominate their statistical counterparts (at a nominal SNR of 10). It may, however, be possible to mitigate the loss in SNR by allowing for templates with unphysical values of {\eta}.

#### Jul 23, 2012

1207.3361 (/preprints)
2012-07-23, 11:53 

## [1207.4956] EMRI data analysis with a phenomenological waveform

Authors: Yan Wang, Yu Shang, Stanislav Babak

Date: 20 Jul 2012

Abstract: Extreme mass ratio inspirals (EMRIs) (capture and inspiral of a compact stellar mass object into a Massive Black Hole (MBH)) are among the most interesting objects for the gravitational wave astronomy. It is a very challenging task to detect those sources with the accurate estimation parameters of binaries primarily due to a large number of the secondary maxima on the likelihood surface. Search algorithms based on the matched filtering require computation of the gravitational waveform hundreds of thousands of times, which is currently not feasible with the most accurate (faithful) models of EMRIs. Here we propose to use a phenomenological template family which covers a large range of EMRIs parameter space. We use these phenomenological templates to detect the signal in the simulated data and then, assuming a particular EMRI model, estimate the physical parameters of the binary. We have separated the detection problem, which is done in a model-independent way, from the parameter estimation. For the latter one, we need to adopt the model for inspiral in order to map phenomenological parameters onto the physical parameter characterizing EMRIs.

#### Jul 23, 2012

1207.4956 (/preprints)
2012-07-23, 08:26 

## [1207.4848] Prospects for observing ultra-compact binaries with space-based gravitational wave interferometers and optical telescopes

Authors: Tyson B. Littenberg, Shane L. Larson, Gijs Nelemans, Neil J. Cornish

Date: 20 Jul 2012

Abstract: Space-based gravitational wave interferometers are sensitive to the galactic population of ultra-compact binaries. An important subset of the ultra-compact binary population are those stars that can be individually resolved by both gravitational wave interferometers and electromagnetic telescopes. The aim of this paper is to quantify the multi-messenger potential of space-based interferometers with arm-lengths between 1 and 5 Gm. The Fisher Information Matrix is used to estimate the number of binaries from a model of the Milky Way which are localized on the sky by the gravitational wave detector to within 1 deg$ˆ2$ and bright enough to be detected by a magnitude limited survey. We find, depending on the choice of GW detector characteristics, limiting magnitude, and observing strategy, that up to a few hundred gravitational wave sources could be detected in electromagnetic follow-up observations.

#### Jul 23, 2012

1207.4848 (/preprints)
2012-07-23, 08:26 

## [1207.4759] Testing general relativity with gravitational waves: a reality check

Authors: Michele Vallisneri

Date: 19 Jul 2012

Abstract: The observations of gravitational-wave signals from astrophysical sources such as binary inspirals will be used to test general relativity for self consistency and against alternative theories of gravity. I describe a simple formula that can be used to characterize the prospects of such tests, by estimating the matched-filtering signal-to-noise ratio required to detect non-general-relativistic corrections of a given magnitude. The formula is valid for sufficiently strong signals; it requires the computation of a single number (the fitting factor between the general-relativistic and corrected waveform families); and it can be applied to all tests that embed general-relativity in a larger theory, including tests of individual theories such as Brans--Dicke gravity, as well as the phenomenological schemes that introduce corrections and extra terms in the post-Newtonian phasing expressions of inspiral waveforms. Using the formula, I show on very general grounds that the volume-limited gravitational-wave searches performed with second-generation ground-based detectors would detect alternative-gravity corrections to general-relativistic waveforms as small as 1--10% (i.e., fitting factors of 0.9 to 0.99).

#### Jul 19, 2012

1207.4759 (/preprints)
2012-07-19, 21:45 

## [1207.4253] Quasinormal-mode spectrum of Kerr black holes and its geometric interpretation

Authors: Huan Yang, David A. Nichols, Fan Zhang, Aaron Zimmerman, Zhongyang Zhang, Yanbei Chen

Date: 18 Jul 2012

Abstract: There is a well-known, intuitive geometric correspondence between high-frequency QNMs of Schwarzschild black holes and null geodesics that reside on the light-ring : the real part of the mode's frequency relates to the geodesic's orbital frequency, and the imaginary part of the frequency corresponds to the Lyapunov exponent of the orbit. For slowly rotating black holes, the QNM real frequency is a linear combination of a the orbit's precessional and orbital frequencies, but the correspondence is otherwise unchanged. In this paper, we find a relationship between the QNM frequencies of Kerr black holes of arbitrary (astrophysical) spins and general spherical photon orbits, which is analogous to the relationship for slowly rotating holes. To derive this result, we first use the WKB approximation to compute accurate algebraic expressions for large-l QNM frequencies. Comparing our WKB calculation to the leading-order, geometric-optics approximation to scalar-wave propagation in the Kerr spacetime, we then draw a correspondence between the real parts of the parameters of a QNM and the conserved quantities of spherical photon orbits. At next-to-leading order in this comparison, we relate the imaginary parts of the QNM parameters to coefficients that modify the amplitude of the scalar wave. With this correspondence, we find a geometric interpretation to two features of the QNM spectrum of Kerr black holes: First, for Kerr holes rotating near the maximal rate, a large number of modes have nearly zero damping; we connect this characteristic to the fact that a large number of spherical photon orbits approach the horizon in this limit. Second, for black holes of any spins, the frequencies of specific sets of modes are degenerate; we find that this feature arises when the spherical photon orbits corresponding to these modes form closed (as opposed to ergodically winding) curves.

#### Jul 18, 2012

1207.4253 (/preprints)
2012-07-18, 18:55 

## [1207.3805] Gravitational Waves from Fallback Accretion onto Neutron Stars

Authors: Anthony L. Piro (Caltech), Eric Thrane (University of Minnesota)

Date: 16 Jul 2012

Abstract: Massive stars generally end their lives as neutron stars (NSs) or black holes (BHs), with NS formation typically occurring at the low mass end and collapse to a BH more likely at the high mass end. In an intermediate regime, with a mass range that depends on the uncertain details of rotation and mass loss during the star's life, a NS is initially formed which then experiences fallback accretion and collapse to a BH. The electromagnetic consequence of such an event is not clear. Depending on the progenitor's structure, possibilities range from a long gamma-ray burst to a Type II supernova (that may or may not be jet-powered) to a collapse with a weak electromagnetic signature. Gravitational waves (GWs) provide the exciting opportunity to peer through the envelope of a dying massive star and directly probe what is occurring inside. We explore whether fallback onto young NSs can be detected by ground-based interferometers. When the incoming material has sufficient angular momentum to form a disk, the accretion spins up the NS sufficiently to produce non-axisymmetric instabilities and gravitational radiation at frequencies of ~700-2400 Hz for ~30-3000 s until collapse to a BH occurs. Using a realistic excess cross-power search algorithm, we show that such events are detectable by Advanced LIGO out to ~17 Mpc. From the rate of nearby core-collapse supernovae, we estimate that there will be ~1-2 events each year that are worth checking for fallback GWs. The observation of these unique GW signatures coincident with electromagnetic detections would identify the transient events that are associated with this channel of BH formation, while providing information about the protoneutron star progenitor.

#### Jul 17, 2012

1207.3805 (/preprints)
2012-07-17, 18:49 

## [1207.3088] Towards models of gravitational waveforms from generic binaries: A simple approximate mapping between precessing and non-precessing inspiral signals

Authors: Patricia Schmidt, Mark Hannam, Sascha Husa

Date: 12 Jul 2012

Abstract: One of the greatest theoretical challenges in the build-up to the era of second-generation gravitational-wave detectors is the modeling of generic binary waveforms. We introduce an approximation that has the potential to significantly simplify this problem. We show that generic precessing-binary inspiral waveforms (covering a seven-dimensional parameter space) can be mapped to only a two-dimensional space of non-precessing binaries, characterized by the mass ratio and a single effective total spin. The mapping consists of a time-dependent rotation of the waveforms into the quadrupole-aligned frame, and is extremely accurate (matches $> 0.99$ with parameter biases in the total spin of $\Delta \chi \leq 0.04$), even in the case of transitional precession. In addition, we demonstrate a simple method to construct hybrid post-Newtonian--numerical-relativity precessing-binary waveforms in the quadrupole-aligned frame, and provide evidence that our approximate mapping can be used all the way to the merger. Finally, based on these results, we outline a general proposal for the construction of generic waveform models, which will be the focus of future work.

#### Jul 16, 2012

1207.3088 (/preprints)
2012-07-16, 00:34 

## [1207.2839] Self Force Orbit-Integrated gravitational waveforms for E(I)MRIs

Authors: Lior M. Burko, Kristen A. Lackeos

Date: 12 Jul 2012

Abstract: We present the first orbit-integrated self force effects for an IMRI or EMRI source, specifically the effects of its conservative piece on the orbit and on the waveform. We consider the quasi-circular motion of a particle in the spacetime of a Schwarzschild black hole, find the orbit and the corresponding gravitational waveform, and discuss the importance of the conservative piece of the self force in detection and parameter estimation. We also show the effect of the conservative piece of the self force on gauge invariant quantities, specifically $uˆt$ as a function of the angular frequency $\Omega$. For long templates the inclusion of the conservative piece is crucial for gravitational-wave astronomy, yet may be ignored for short templates with little effect on detection rate.

#### Jul 12, 2012

1207.2839 (/preprints)
2012-07-12, 23:10 

## [1207.2497] Constraining Intermediate-Mass Black Holes in Globular Clusters

Authors: Stefan Umbreit, Frederic A. Rasio

Date: 10 Jul 2012

Abstract: Decades after the first predictions of intermediate-mass black holes (IMBHs) in globular clusters (GCs) there is still no unambiguous observational evidence for their existence. The most promising signatures for IMBHs are found in the cores of GCs, where the evidence now comes from the stellar velocity distribution, the surface density profile, and, for very deep observations, the mass-segregation profile near the cluster center. However, interpretation of the data, and, in particular, constraints on central IMBH masses, require the use of detailed cluster dynamical models. Here we present results from Monte Carlo cluster simulations of GCs that harbor IMBHs. As an example of application, we compare velocity dispersion, surface brightness and mass-segregation profiles with observations of the GC M10, and constrain the mass of a possible central IMBH in this cluster. We find that, although M10 does not seem to possess a cuspy surface density profile, the presence of an IMBH with a mass up to 0.75% of the total cluster mass, corresponding to about 600 Msun, cannot be excluded. This is also in agreement with the surface brightness profile, although we find it to be less constraining, as it is dominated by the light of giants, causing it to fluctuate significantly. We also find that the mass-segregation profile cannot be used to discriminate between models with and without IMBH. The reason is that M10 is not yet dynamically evolved enough for the quenching of mass segregation to take effect. Finally, detecting a velocity dispersion cusp in clusters with central densities as low as in M10 is extremely challenging, and has to rely on only 20-40 bright stars. It is only when stars with masses down to 0.3 Msun are included that the velocity cusp is sampled close enough to the IMBH for a significant increase above the core velocity dispersion to become detectable.

#### Jul 11, 2012

1207.2497 (/preprints)
2012-07-11, 23:12 

## [1207.0769] Horizon-absorption effects in coalescing black-hole binaries: An effective-one-body study of the non-spinning case

Authors: Sebastiano Bernuzzi, Alessandro Nagar, Anil Zenginoglu

Date: 3 Jul 2012

Abstract: We study the horizon absorption of gravitational waves in coalescing, circularized, nonspinning black hole binaries. The horizon absorbed fluxes of a binary with a large mass ratio (q=1000) obtained by numerical perturbative simulations are compared with an analytical, effective-one-body (EOB) resummed expression recently proposed. The perturbative method employs an analytical, linear in the mass ratio, effective-one-body (EOB) resummed radiation reaction, and the Regge-Wheeler-Zerilli (RWZ) formalism for wave extraction. Hyperboloidal (transmitting) layers are employed for the numerical solution of the RWZ equations to accurately compute horizon fluxes up to the late plunge phase. The horizon fluxes from perturbative simulations and the EOB-resummed expression agree at the level of a few percent down to the late plunge. An upgrade of the EOB model for nonspinning binaries that includes horizon absorption of angular momentum as an additional term in the resummed radiation reaction is then discussed. The effect of this term on the waveform phasing for binaries with mass ratios spanning 1 to 1000 is investigated. We confirm that for comparable and intermediate-mass-ratio binaries horizon absorbtion is practically negligible for detection with advanced LIGO and the Einstein Telescope (faithfulness greater than or equal to 0.997).

#### Jul 05, 2012

1207.0769 (/preprints)
2012-07-05, 09:27 

## [1207.0001] Gravitational waves from spinning eccentric binaries

Authors: P&#xe9;ter Csizmadia, Gergely Debreczeni, Istv&#xe1;n R&#xe1;cz, M&#xe1;ty&#xe1;s Vas&#xfa;th

Date: 29 Jun 2012

Abstract: This paper is to introduce a new software called CBwaves which provides a fast and accurate computational tool to determine the gravitational waveforms yielded by generic spinning binaries of neutron stars and/or black holes on eccentric orbits. This is done within the post-Newtonian (PN) framework by integrating the equations of motion and the spin precession equations while the radiation field is determined by a simultaneous evaluation of the analytic waveforms. In applying CBwaves various physically interesting scenarios have been investigated. In particular, we have studied the appropriateness of the adiabatic approximation, and justified that the energy balance relation is indeed insensitive to the specific form of the applied radiation reaction term. By studying eccentric binary systems it is demonstrated that circular template banks are very ineffective in identifying binaries even if they possess tiny residual orbital eccentricity. In addition, by investigating the validity of the energy balance relation we show that, on contrary to the general expectations, the post-Newtonian approximation should not be applied once the post-Newtonian parameter gets beyond the critical value $\sim 0.08-0.1$. Finally, by studying the early phase of the gravitational waves emitted by strongly eccentric binary systems — which could be formed e.g. in various many-body interactions in the galactic halo — we have found that they possess very specific characteristics which may be used to identify these type of binary systems.

#### Jul 02, 2012

1207.0001 (/preprints)
2012-07-02, 22:10 

## [1206.7087] The dynamics of the gravitational two-body problem in the post-Newtonian approximation at quadratic order in the Newton's constant

Authors: Stefano Foffa, Riccardo Sturani

Date: 29 Jun 2012

Abstract: We derive the conservative part of the Lagrangian and the energy of a gravitationally bound two-body system at fourth post-Newtonian order, up to terms quadratic in the Newton's constant. We also show that such terms are compatible with Lorentz invariance and we write an ansatz for the center-of mass position. The remaining terms carrying higher powers of the Newton constant are currently under investigation.

#### Jul 01, 2012

1206.7087 (/preprints)
2012-07-01, 22:40