## [0901.4696] Searching for numerically-simulated signals of black hole binaries with a phenomenological template family

Authors: Lucia Santamaria, Badri Krishnan, John T. Whelan

Date: 29 Jan 2009

Abstract: Recent progress in numerical relativity now allows computation of the binary black hole merger, whereas post-Newtonian and perturbative techniques can be used to model the inspiral and ringdown phases. So far, most gravitational-wave searches have made use of various post-Newtonian-inspired templates to search for signals arising from the coalescence of compact binary objects. Ajith et al have produced hybrid waveforms for non-spinning binary black-hole systems which include the three stages of the coalescence process, and constructed from them phenomenological templates which capture the features of these waveforms in a parametrized form. As a first step towards extending the present inspiral searches to higher-mass binary black-hole systems, we have used these phenomenological waveforms in a search for numerically-simulated signals injected into synthetic LIGO data as part of the NINJA project.

#### Jan 30, 2009

0901.4696 (/preprints)
2009-01-30, 10:07 

## [0901.4343] Analytic study of mass segregation around a massive black hole

Authors: Uri Keshet, Clovis Hopman, Tal Alexander

Date: 28 Jan 2009

Abstract: We analyze the distribution of stars of arbitrary mass function g(m) around a massive black hole (MBH). Unless g is strongly dominated by light stars, the steady-state distribution function approaches a power-law in specific energy x=-E/(m*sigmaˆ2)<x_max with index p=m/4M_0, where E is the energy, sigma the typical velocity dispersion of unbound stars, and M_0 the mass averaged over m*g*x_{max}ˆp. For light-dominated g, p becomes non-linear in m and can grow as large as 3/2 - much steeper than previously thought. A simple prescription for the stellar density profile around MBHs is provided.

#### Jan 29, 2009

0901.4343 (/preprints)
2009-01-29, 08:13 

## [0901.4399] Testing gravitational-wave searches with numerical relativity waveforms: Results from the first Numerical INJection Analysis (NINJA) project

Authors: Benjamin Aylott, John G. Baker, William D. Boggs, Michael Boyle, Patrick R. Brady, Duncan A. Brown, Bernd Br&#xfc;gmann, Luisa T. Buchman, Alessandra Buonanno, Laura Cadonati, Jordan Camp, Manuela Campanelli, Joan Centrella, Shourov Chatterji, Nelson Christensen, Tony Chu, Peter Diener, Nils Dorband, Zachariah B. Etienne, Joshua Faber, Stephen Fairhurst, Benjamin Farr, Sebastian Fischetti, Gianluca Guidi, Lisa M. Goggin, Mark Hannam, Frank Herrmann, Ian Hinder, Sascha Husa, Vicky Kalogera, Drew Keppel, Lawrence E. Kidder, Bernard J. Kelly, Badri Krishnan, Pablo Laguna, Carlos O. Lousto, Ilya Mandel, Pedro Marronetti, Richard Matzner, Sean T. McWilliams, Keith D. Matthews, R. Adam Mercer, Satyanarayan R. P. Mohapatra, Abdul H. Mrou&#xe9;, Hiroyuki Nakano, Evan Ochsner, Yi Pan, Larne Pekowsky, Harald P. Pfeiffer, Denis Pollney, Frans Pretorius, Vivien Raymond, Christian Reisswig, Luciano Rezzolla, Oliver Rinne, Craig Robinson, Christian R&#xf6;ver, Luc&#xed;a Santamar&#xed;a, Bangalore Sathyaprakash, Mark A. Scheel, Erik Schnetter, Jennifer Seiler, Stuart L. Shapiro, Deirdre Shoemaker, Ulrich Sperhake, Alexander Stroeer, Riccardo Sturani, Wolfgang Tichy, Yuk Tung Liu, Marc van der Sluys, James R. van Meter, Ruslan Vaulin, Alberto Vecchio, John Veitch, Andrea Vicer&#xe9;, John T. Whelan, Yosef Zlochower

Date: 28 Jan 2009

Abstract: The Numerical INJection Analysis (NINJA) project is a collaborative effort between members of the numerical relativity and gravitational-wave data analysis communities. The purpose of NINJA is to study the sensitivity of existing gravitational-wave search algorithms using numerically generated waveforms and to foster closer collaboration between the numerical relativity and data analysis communities. We describe the results of the first NINJA analysis which focused on gravitational waveforms from binary black hole coalescence. Ten numerical relativity groups contributed numerical data which were used to generate a set of gravitational-wave signals. These signals were injected into a simulated data set, designed to mimic the response of the Initial LIGO and Virgo gravitational-wave detectors. Nine groups analysed this data using search and parameter-estimation pipelines. Matched filter algorithms, un-modelled-burst searches and Bayesian parameter-estimation and model-selection algorithms were applied to the data. We report the efficiency of these search methods in detecting the numerical waveforms and measuring their parameters. We describe preliminary comparisons between the different search methods and suggest improvements for future NINJA analyses.

#### Jan 29, 2009

0901.4399 (/preprints)
2009-01-29, 08:12 

## [0901.4365] Black holes in general relativity

Authors: Matt Visser (Victoria University of Wellington)

Date: 28 Jan 2009

Abstract: What is going on (as of August 2008) at the interface between theoretical general relativity, string-inspired models, and observational astrophysics? Quite a lot. In this mini-survey I will make a personal choice and focus on four specific questions: Do black holes "exist"? (For selected values of the word "exist".) Is black hole formation and evaporation unitary? Can one mimic a black hole to arbitrary accuracy? Can one detect the presence of a horizon using local physics?

#### Jan 29, 2009

0901.4365 (/preprints)
2009-01-29, 08:11 

## [0901.4162] A Quintet of Black Hole Mass Determinations

Authors: Kayhan Gultekin (1), Douglas O. Richstone (1), Karl Gebhardt (2), Tod R. Lauer (3), Jason Pinkney (4), M. C. Aller (5), Ralf Bender (6), Alan Dressler (7), S. M. Faber (8), Alexei V. Filippenko (9), Richard Green (10), Luis C. Ho (7), John Kormendy (2), Christos Siopis (11) ((1) Dept. of Astronomy, University of Michigan, (2) Department of Astronomy, University of Texas, (3) National Optical Astronomy Observatory, (4) Department of Physics and Astronomy, Ohio Northern University, (5) Department of Physics, Institute of Astronomy, ETH Zurich, (6) Universitaets-Sternwarte der Ludwig-Maximilians-Universit&#xe4;t, (7) Observatories of the Carnegie Institution of Washington, (8) University of California Observatories/Lick Observatory, Board of Studies in Astronomy and Astrophysics, University of California, Santa Cruz, (9) Department of Astronomy, University of California, Berkeley, (10) LBT Observatory, University of Arizona, (11) Institut d&#x27;Astronomie et d&#x27;Astrophysique, Universit&#xe9; Libre de Bruxelles)

Date: 27 Jan 2009

Abstract: We report five new measurements of central black hole masses based on STIS and WFPC2 observations with the Hubble Space Telescope and on axisymmetric, three-integral, Schwarzschild orbit-library kinematic models. We selected a sample of galaxies within a narrow range in velocity dispersion that cover a range of galaxy parameters (including Hubble type and core/power-law surface density profile) where we expected to be able to resolve the galaxy's sphere of influence based on the predicted value of the black hole mass from the M-sigma relation. We find masses in units of 10ˆ8 solar masses for the following galaxies:
NGC 3585, M_BH = 3.4 (+1.5, -0.6);
NGC 3607, M_BH = 1.2 (+0.4, -0.4);
NGC 4026, M_BH = 2.1 (+0.7, -0.4); and
NGC 5576, M_BH = 1.0 (+0.5, -0.3), all significantly excluding M_BH = 0. For
NGC 3945, M_BH = 0.09 (+0.17, -0.21), which is significantly below predictions from M-sigma and M-L relations and consistent with M_BH = 0, though the presence of a double bar in this galaxy may present problems for our axisymmetric code.

#### Jan 28, 2009

0901.4162 (/preprints)
2009-01-28, 08:23 

## [0901.4133] Constraining the Spin-down of the Nearby Isolated Neutron Star RX J2143.0 0654

Authors: D. L. Kaplan, M. H. van Kerkwijk

Date: 26 Jan 2009

Abstract: Magnetic field estimates for nearby isolated neutron stars (INS) help to constrain both the characteristics of the population and the nature of their peculiar X-ray spectra. From a series of XMM-Newton observations of RX J2143.0+0654, we measure a spin-down rate of -4.6e-16 +/- 2.0e-16 Hz/s. While this does not allow a definitive measurement of the dipole magnetic field strength, fields of >1e14 G such as those inferred from the presence of a spectral absorption feature at 0.75keV are excluded. Instead, the field is most likely around 2e13 G, very similar to those of other INS. We not only suggest that this similarity most likely reflects the influence of magnetic field decay on this population, but also discuss a more speculative possibility that it results from peculiar conditions on the neutron-star surface. We find no evidence for spectral variability above the ~2% level. We confirm the presence of the 0.75-keV feature found earlier, and find tentative evidence for an additional absorption feature at 0.4 keV.

#### Jan 28, 2009

0901.4133 (/preprints)
2009-01-28, 08:23 

## [0901.1667] Extreme mass ratio inspiral rates: dependence on the massive black hole mass

Authors: Clovis Hopman (Leiden Observatory)

Date: 12 Jan 2009

Abstract: We study the rate at which stars spiral into a massive black hole (MBH) due to the emission of gravitational waves (GWs), as a function of the mass M of the MBH. In the context of our model, it is shown analytically that the rate approximately depends on the MBH mass as Mˆ{-¼}. Numerical simulations confirm this result, and show that for all MBH masses, the event rate is highest for stellar black holes, followed by white dwarfs, and lowest for neutron stars. The Laser Interferometer Space Antenna (LISA) is expected to see hundreds of these extreme mass ratio inspirals per year. Since the event rate derived here formally diverges as M->0, the model presented here cannot hold for MBHs of masses that are too low, and we discuss what the limitations of the model are.

#### Jan 27, 2009

0901.1667 (/preprints)
2009-01-27, 08:36 

## [0901.3779] A Candidate Sub-Parsec Supermassive Binary Black Hole System

Authors: Todd A. Boroson (NOAO), Tod R. Lauer (NOAO)

Date: 23 Jan 2009

Abstract: We identify SDSS J153636.22+044127.0, a QSO discovered in the Sloan Digital Sky Survey, as a promising candidate for a binary black hole system. This QSO has two broad-line emission systems separated by 3500 km/sec. The redder system at z=0.3889 also has a typical set of narrow forbidden lines. The bluer system (z=0.3727) shows only broad Balmer lines and UV Fe II emission, making it highly unusual in its lack of narrow lines. A third system, which includes only unresolved absorption lines, is seen at a redshift, z=0.3878, intermediate between the two emission-line systems. While the observational signatures of binary nuclear black holes remain unclear, J1536+0441 is unique among all QSOs known in having two broad-line regions, indicative of two separate black holes presently accreting gas. The interpretation of this as a bound binary system of two black holes having masses of 10ˆ8.9 and 10ˆ7.3 solar masses, yields a separation of ~ 0.1 parsec and an orbital period of ~100 years. The separation implies that the two black holes are orbiting within a single narrow-line region, consistent with the characteristics of the spectrum. This object was identified as an extreme outlier of a Karhunen-Loeve Transform of 17,500 z < 0.7 QSO spectra from the SDSS. The probability of the spectrum resulting from a chance superposition of two QSOs with similar redshifts is estimated at 2X10ˆ-7, leading to the expectation of 0.003 such objects in the sample studied; however, even in this case, the spectrum of the lower redshift QSO remains highly unusual.

#### Jan 27, 2009

0901.3779 (/preprints)
2009-01-27, 08:35 

## [0901.1778] The Galactic Gravitational wave foreground

Authors: G. Nelemans (Nijmegen)

Date: 13 Jan 2009

Abstract: I present an overview of the Galactic binaries that form the foreground for the ESA/NASA Laser Interferometer Space Antenna (LISA). The currently known population is discussed, as well as current and near-future large-scale surveys that will find new systems. The astrophysics that can be done when the LISA data becomes available is presented, with particular attention to verification binaries, the overall Galactic populations, neutron star and black hole binaries and sources in globular clusters. I discuss the synergy with electro-magnetic observations and correct an error in the estimate of the number of LISA systems that can be found in the optical compared to Nelemans (2006a) and conclude that at least several hundreds of systems should be detectable.

#### Jan 27, 2009

0901.1778 (/preprints)
2009-01-27, 08:34 

## [0901.3861] Comparison of Post-Newtonian and Numerical Evolutions of Black-Hole Binaries

Authors: Hiroyuki Nakano, Manuela Campanelli, Carlos O. Lousto, Yosef Zlochower

Date: 24 Jan 2009

Abstract: In this paper, we compare the waveforms from the post-Newtonian (PN) approach with the numerical simulations of generic black-hole binaries which have mass ratio $q\sim0.8$, arbitrarily oriented spins with magnitudes $S_1/m_1ˆ2\sim0.6$ and $S_2/m_2ˆ2\sim0.4$, and orbit 9 times from an initial orbital separation of $r\approx11M$ prior to merger. We observe a reasonably good agreement between the PN and numerical waveforms, with an overlap of over 98% for the first six cycles of the $(\ell=2,m=\pm2)$ mode and over 90% for the $(\ell=2,m=1)$ and $(\ell=3,m=3)$ modes.

#### Jan 27, 2009

0901.3861 (/preprints)
2009-01-27, 08:33 

## [0901.3511] Proper Star Direction and Physical Reference Frames linked via General Relativistic definition of Astrometric Measurement I. Stellar Aberration

Authors: Mariateresa Crosta (1), Alberto Vecchiato (1) ((1) INAF - Astronomical Observatory of Torino)

Date: 22 Jan 2009

Abstract: The high accuracy of modern space astrometry requires the use of General Relativity to model the propagation of stellar light through the gravitational field encountered from a source to a given observer inside the Solar System. In this sense relativistic astrometry is part of fundamental physics. The general relativistic definition of astrometric measurement needs an appropriate use of the concept of reference frame, which should then be linked to the conventions of the IAU Resolutions (2000), which fix the celestial coordinate system. A consistent definition of the astrometric observables in the context of General Relativity is also essential to find uniquely the stellar coordinates and proper motion, this being the main physical task of the inverse ray tracing problem. Aim of this work is to set the level of reciprocal consistency of two relativistic models, GREM and RAMOD (Gaia, ESA mission), in order to garantee a physically correct definition of light direction to a star, an essential item for deducing the star coordinates and proper motion within the same level of measurement accuracy.

#### Jan 26, 2009

0901.3511 (/preprints)
2009-01-26, 08:36 

## [astro-ph/0605637] Gravitational polarization and the phenomenology of MOND

Authors: Luc Blanchet

Date: 24 May 2006

Abstract: The modified Newtonian dynamics (MOND) has been proposed as an alternative to the dark matter paradigm; the philosophy behind is that there is no dark matter and we witness a violation of the Newtonian law of dynamics. In this article, we interpret differently the phenomenology sustaining MOND, as resulting from an effect of "gravitational polarization", of some cosmic fluid made of dipole moments, aligned in the gravitational field, and representing a new form of dark matter. We invoke an internal force, of non-gravitational origin, in order to hold together the microscopic constituents of the dipole. The dipolar particles are weakly influenced by the distribution of ordinary matter; they are accelerated not by the gravitational field, but by its gradient, or tidal gravitational field.

#### Jan 26, 2009

0605637 (/preprints/astro-ph)
2009-01-26, 08:34 

## [astro-ph/0507692] Gravitational Recoil of Inspiralling Black-Hole Binaries to Second Post-Newtonian Order

Authors: Luc Blanchet, Moh&#x27;d S. S. Qusailah, Clifford M. Will

Date: 29 Jul 2005

Abstract: The loss of linear momentum by gravitational radiation and the resulting gravitational recoil of black-hole binary systems may play an important role in the growth of massive black holes in early galaxies. We calculate the gravitational recoil of non-spinning black-hole binaries at the second post-Newtonian order (2PN) beyond the dominant effect, obtaining, for the first time, the 1.5PN correction term due to tails of waves and the next 2PN term. We find that the maximum value of the net recoil experienced by the binary due to the inspiral phase up to the innermost stable circular orbit (ISCO) is of the order of 22 km/s. We then estimate the kick velocity accumulated during the plunge from the ISCO up to the horizon by integrating the momentum flux using the 2PN formula along a plunge geodesic of the Schwarzschild metric. We find that the contribution of the plunge dominates over that of the inspiral. For a mass ratio m_2/m_1=1/8, we estimate a total recoil velocity (due to both adiabatic and plunge phases) of 100 +/- 20 km/s. For a ratio 0.38, the recoil is maximum and we estimate it to be 250 +/- 50 km/s. In the limit of small mass ratio, we estimate V/c to be approximately 0.043 (1 +/- 20%)(m_2/m_1)ˆ2. Our estimates are consistent with, but span a substantially narrower range than, those of Favata et al. (2004).

#### Jan 26, 2009

0507692 (/preprints/astro-ph)
2009-01-26, 08:34 

## [0901.1661] General Properties of the Gravitational Wave Spectrum from Phase Transitions

Authors: Chiara Caprini, Ruth Durrer, Thomas Konstandin, Geraldine Servant

Date: 12 Jan 2009

Abstract: In this paper we discuss some general aspects of the gravitational wave background arising from post-inflationary short-lasting cosmological events such as phase transitions. We concentrate on the physics which determines the shape and the peak frequency of the gravitational wave spectrum. We then apply our general findings to the case of bubble collisions during a first order phase transition and compare different results in the recent literature.

#### Jan 26, 2009

0901.1661 (/preprints)
2009-01-26, 08:33 

## [0901.3762] Enhancing the capabilities of LIGO time-frequency plane searches through clustering

Authors: Rubab Khan, Shourov Chatterji

Date: 23 Jan 2009

Abstract: One class of gravitational wave signals LIGO is searching for consists of short duration bursts of unknown waveforms. Potential sources include core collapse supernovae, gamma ray burst progenitors, and the merger of binary black holes or neutron stars. We present a density-based clustering algorithm to improve the performance of time-frequency searches for the such gravitational-wave bursts when they are extended in time and/or frequency. We have implemented this algorithm as an extension to the QPipeline search for bursts, which currently determines the statistical significance of events based solely on the peak significance observed in minimum uncertainty regions of the time-frequency plane. Density based clustering improves the performance of such a search by considering the aggregate significance of arbitrarily shaped regions in the time-frequency plane and rejecting the isolated minimum uncertainty features expected from the background detector noise. In this paper, we present test results for simulated signals and demonstrate that density based clustering improves the performance of the QPipeline for signals that are extended in time and/or frequency.

#### Jan 26, 2009

0901.3762 (/preprints)
2009-01-26, 08:32 

## [0812.4063] Relativistic orbits with gravitomagnetic corrections

Authors: S. Capozziello, M. De Laurentis, F. Garufi, L. Milano

Date: 20 Dec 2008

Abstract: Corrections to the relativistic orbits are studied considering higher order approximations induced by gravitomagnetic effects. We discuss in details how such corrections come out taking into account magnetic components in the weak field limit of gravitational field and then the theory of orbits is developed starting from the Newtonian one, the lowest order in the approximation. Finally, the orbital structure and the stability conditions are discussed giving numerical examples. Beside the standard periastron corrections of General Relativity, a new nutation effect is due to the cˆ{-3} corrections. The transition to a chaotic behavior strictly depends on the initial conditions. The orbital phase space portrait is discussed.

#### Jan 22, 2009

0812.4063 (/preprints)
2009-01-22, 07:30 

## [0901.3258] Measuring the neutron star equation of state with gravitational wave observations

Authors: Jocelyn S. Read, Charalampos Markakis, Masaru Shibata, Koji Uryu, Jolien D. E. Creighton, John L. Friedman

Date: 21 Jan 2009

Abstract: We report the results of a first study that uses numerical simulations to estimate the accuracy with which one can use gravitational wave observations of double neutron star inspiral to measure parameters of the neutron-star equation of state. The simulations use the evolution and initial-data codes of Shibata and Uryu to compute the last several orbits and the merger of neutron stars, with matter described by a parametrized equation of state. Previous work suggested the use of an effective cutoff frequency to place constraints on the equation of state. We find, however, that greater accuracy is obtained by measuring departures from the point-particle limit of the gravitational waveform produced during the late inspiral.
As the stars approach their final plunge and merger, the gravitational wave phase accumulates more rapidly for smaller values of the neutron star compactness (the ratio of the mass of the neutron star to its radius). We estimate that realistic equations of state will lead to gravitational waveforms that are distinguishable from point particle inspirals at an effective distance (the distance to an optimally oriented and located system that would produce an equivalent waveform amplitude) of 100 Mpc or less. As Lattimer and Prakash observed, neutron-star radius is closely tied to the pressure at density not far above nuclear. Our results suggest that broadband gravitational wave observations at frequencies between 500 and 1000 Hz will constrain this pressure, and we estimate the accuracy with which it can be measured. Related first estimates of radius measurability show that the radius can be determined to an accuracy of ~1 km at 100 Mpc.

#### Jan 22, 2009

0901.3258 (/preprints)
2009-01-22, 07:09 

## [0901.2958] Gravitational-wave confusion background from cosmological compact binaries: Implications for future terrestrial detectors

Authors: Tania Regimbau, Scott A. Hughes

Date: 19 Jan 2009

Abstract: Increasing the sensitivity of a gravitational-wave (GW) detector improves our ability to measure the characteristics of detected sources. It also increases the number of weak signals that contribute to the data. Because GW detectors have nearly all-sky sensitivity, they can be subject to a confusion limit: Many sources which cannot be distinguished may be measured simultaneously, defining a stochastic noise floor to the sensitivity. For GW detectors operating at present and for their planned upgrades, the projected event rate is sufficiently low that we are far from the confusion-limited regime. However, some detectors currently under discussion may have large enough reach to binary inspiral that they enter the confusion-limited regime. In this paper, we examine the binary inspiral confusion limit for terrestrial detectors. We consider a broad range of inspiral rates in the literature, several planned advanced gravitational-wave detectors, and the highly advanced "Einstein Telescope" design. Though most advanced detectors will not be impacted by this limit, the Einstein Telescope with a very low frequency "seismic wall" may be subject to confusion noise. At a minimum, careful data analysis will be require to separate signals which will appear confused. This result should be borne in mind when designing highly advanced future instruments.

#### Jan 21, 2009

0901.2958 (/preprints)
2009-01-21, 06:33 

## [0901.2931] Status of black-hole-binary simulations for gravitational-wave detection

Authors: Mark Hannam

Date: 19 Jan 2009

Abstract: It is now possible to theoretically calculate the gravitational-wave signal from the inspiral, merger and ringdown of a black-hole-binary system. The late inspiral, merger and ringdown can be calculated in full general relativity using numerical methods. The numerical waveforms can then be either stitched to inspiral waveforms predicted by approximation techniques (in particular post-Newtonian calculations) that start at an arbitrarily low frequency, or used to calibrate free parameters in analytic models of the full waveforms. In this review I summarize the status of numerical-relativity (NR) waveforms that include at least ten cycles of the dominant mode of the GW signal before merger, which should be long enough to produce accurate, complete waveforms for GW observations.

#### Jan 21, 2009

0901.2931 (/preprints)
2009-01-21, 06:32 

## [0901.2437] The Samurai Project: verifying the consistency of black-hole-binary waveforms for gravitational-wave detection

Authors: Mark Hannam, Sascha Husa, John G. Baker, Michael Boyle, Bernd Bruegmann, Tony Chu, Nils Dorband, Frank Herrmann, Ian Hinder, Bernard J. Kelly, Lawrence E. Kidder, Pablo Laguna, Keith D. Matthews, James R. van Meter, Harald P. Pfeiffer, Denis Pollney, Christian Reisswig, Mark A. Scheel, Deirdre Shoemaker

Date: 16 Jan 2009

Abstract: We quantify the consistency of numerical-relativity black-hole-binary waveforms for use in gravitational-wave (GW) searches with current and planned ground-based detectors. We compare previously published results for the $(\ell=2,| m | =2)$ mode of the gravitational waves from an equal-mass nonspinning binary, calculated by five numerical codes. We focus on the 1000M (about six orbits, or 12 GW cycles) before the peak of the GW amplitude and the subsequent ringdown. We find that the phase and amplitude agree within each code's uncertainty estimates. The mismatch between the $(\ell=2,| m| =2)$ modes is better than $10ˆ{-3}$ for binary masses above $60 M_{\odot}$ with respect to the Enhanced LIGO detector noise curve, and for masses above $180 M_{\odot}$ with respect to Advanced LIGO, Virgo and Advanced Virgo. Between the waveforms with the best agreement, the mismatch is below $2 \times 10ˆ{-4}$. We find that the waveforms would be indistinguishable in all ground-based detectors (and for the masses we consider) if detected with a signal-to-noise ratio of less than $\approx25$.

#### Jan 19, 2009

0901.2437 (/preprints)
2009-01-19, 07:43 

## [0901.1680] Detecting gravitational waves from accreting neutron stars

Authors: Anna L. Watts (University of Amsterdam), Badri Krishnan (AEI/MPG)

Date: 12 Jan 2009

Abstract: The gravitational waves emitted by neutron stars carry unique information about their structure and composition. Direct detection of these gravitational waves, however, is a formidable technical challenge. In a recent study we quantified the hurdles facing searches for gravitational waves from the known accreting neutron stars, given the level of uncertainty that exists regarding spin and orbital parameters. In this paper we reflect on our conclusions, and issue an open challenge to the theoretical community to consider how searches should be designed to yield the most astrophysically interesting upper limits. With this in mind we examine some more optimistic emission scenarios involving spin-down, and show that there are technically feasible searches, particularly for the accreting millisecond pulsars, that might place meaningful constraints on torque mechanisms. We finish with a brief discussion of prospects for indirect detection.

#### Jan 15, 2009

0901.1680 (/preprints)
2009-01-15, 09:00 

## [0901.1628] Comparison of high-accuracy numerical simulations of black-hole binaries with stationary phase post-Newtonian template waveforms for Initial and Advanced LIGO

Authors: Michael Boyle, Duncan A. Brown, Larne Pekowsky

Date: 12 Jan 2009

Abstract: We study the effectiveness of stationary-phase approximated post-Newtonian waveforms currently used by ground-based gravitational-wave detectors to search for the coalescence of binary black holes by comparing them to an accurate waveform obtained from numerical simulation of an equal-mass non-spinning binary black hole inspiral, merger and ringdown. We perform this study for the Initial- and Advanced-LIGO detectors. We find that overlaps between the templates and signal can be improved by integrating the match filter to higher frequencies than used currently. We propose simple analytic frequency cutoffs for both Initial and Advanced LIGO, which achieve nearly optimal matches, and can easily be extended to unequal-mass, spinning systems. We also find that templates that include terms in the phase evolution up to 3.5 pN order are nearly always better, and rarely significantly worse, than 2.0 pN templates currently in use. For Initial LIGO we recommend a strategy using templates that include a recently introduced pseudo-4.0 pN term in the low-mass ($M \leq 35 \MSun$) region, and 3.5 pN templates allowing unphysical values of the symmetric reduced mass $\eta$ above this. This strategy always achieves overlaps within 0.3% of the optimum, for the data used here. For Advanced LIGO we recommend a strategy using 3.5 pN templates up to $M=12 \MSun$, 2.0 pN templates up to $M=21 \MSun$, pseudo-4.0 pN templates up to $65 \MSun$, and 3.5 pN templates with unphysical $\eta$ for higher masses. This strategy always achieves overlaps within 0.7% of the optimum for Advanced LIGO.

#### Jan 13, 2009

0901.1628 (/preprints)
2009-01-13, 08:37 

## [0812.4395] Numerical modeling of black holes as sources of gravitational waves in a nutshell

Authors: Sascha Husa

Date: 23 Dec 2008

Abstract: These notes summarize basic concepts underlying numerical relativity and in particular the numerical modeling of black hole dynamics as a source of gravitational waves. Main topics are the 3+1 decomposition of general relativity, the concept of a well-posed initial value problem, the construction of initial data for general relativity, trapped surfaces and gravitational waves. Also, a brief summary is given of recent progress regarding the numerical evolution of black hole binary systems.

#### Jan 09, 2009

0812.4395 (/preprints)
2009-01-09, 12:13 

## [0812.4413] Recoil velocity at 2PN order for spinning black hole binaries

Authors: Etienne Racine, Alessandra Buonanno, Lawrence E. Kidder

Date: 23 Dec 2008

Abstract: We compute the flux of linear momentum carried by gravitational waves emitted from spinning binary black holes at 2PN order for generic orbits. In particular we provide explicit expressions of three new types of terms, namely next-to-leading order spin-orbit terms at 1.5 PN order, spin-orbit tail terms at 2PN order, and spin-spin terms at 2PN order. Restricting ourselves to quasi-circular orbits, we integrate the linear momentum flux over time to obtain the recoil velocity as function of orbital frequency. We find that in the so-called superkick configuration the higher-order spin corrections can increase the recoil velocity up to about a factor 3 with respect to the leading-order PN prediction. Furthermore, we provide expressions valid for generic orbits, and accurate at 2PN order, for the energy and angular momentum carried by gravitational waves emitted from spinning binary black holes. Specializing to quasi-circular orbits we compute the spin-spin terms at 2PN order in the expression for the evolution of the orbital frequency and found agreement with Mik\'{o}czi, Vas\'{u}th and Gergely. We also verified that in the limit of extreme mass ratio our expressions for the energy and angular momentum fluxes match the ones of Tagoshi, Shibata, Tanaka and Sasaki obtained in the context of black hole perturbation theory.

#### Jan 09, 2009

0812.4413 (/preprints)
2009-01-09, 12:13 

## [0812.4339] Gravitational wave background as a probe of the primordial black hole abundance

Authors: Ryo Saito, Jun&#x27;ichi Yokoyama

Date: 23 Dec 2008

Abstract: Formation of primordial black holes (PBHs) requires a large root-mean-square amplitude of density fluctuations, which generate second-order tensor perturbations that can be compared with observational constraints. We show that pulsar timing data essentially rules out PBHs with $10ˆ{2-4}\msolar$ which were previously considered as a candidate of intermediate-mass black hoes and that PBHs with mass range $10ˆ{20-26}$ g may be probed by future space-based laser interferometers.

#### Jan 09, 2009

0812.4339 (/preprints)
2009-01-09, 12:13 

## [0812.4302] Degeneracies in Sky Localisation Determination from a Spinning Coalescing Binary through Gravitational Wave Observations: a Markov-Chain Monte-Carlo Analysis for two Detectors

Authors: V. Raymond, M.V. van der Sluys, I. Mandel, V. Kalogera, C. Roever, N. Christensen

Date: 22 Dec 2008

Abstract: Gravitational-wave signals from inspirals of binary compact objects (black holes and neutron stars) are primary targets of the ongoing searches by ground-based gravitational-wave interferometers (LIGO, Virgo, and GEO-600). We present parameter-estimation simulations for inspirals of black-hole--neutron-star binaries using Markov-chain Monte-Carlo methods. As a specific example of the power of these methods, we consider source localisation in the sky and analyse the degeneracy in it when data from only two detectors are used. We focus on the effect that the black-hole spin has on the localisation estimation. We also report on a comparative Markov-chain Monte-Carlo analysis with two different waveform families, at 1.5 and 3.5 post-Newtonian order.

#### Jan 09, 2009

0812.4302 (/preprints)
2009-01-09, 12:13 

## [gr-qc/0507083] Lunar Laser Ranging Tests of the Equivalence Principle with the Earth and Moon

Authors: James G. Williams, Slava G. Turyshev, Dale H. Boggs

Date: 19 Jul 2005

Abstract: A primary objective of the Lunar Laser Ranging (LLR) experiment is to provide precise observations of the lunar orbit that contribute to a wide range of science investigations. Time series of the highly accurate measurements of the distance between the Earth and Moon provide unique information used to determine whether, in accordance with the Equivalence Principle (EP), both of these celestial bodies are falling towards the Sun at the same rate, despite their different masses, compositions, and gravitational self-energies. Current LLR solutions give $(-1.0 \pm 1.4) \times 10ˆ{-13}$ for any possible inequality in the ratios of the gravitational and inertial masses for the Earth and Moon, $\Delta(M_G/M_I)$. This result, in combination with laboratory experiments on the weak equivalence principle, yields a strong equivalence principle (SEP) test of $\Delta(M_G/M_I)_{\tt SEP} = (-2.0 \pm 2.0) \times 10ˆ{-13}$. Such an accurate result allows other tests of gravitational theories. The result of the SEP test translates into a value for the corresponding SEP violation parameter $\eta$ of $(4.4 \pm 4.5)\times10ˆ{-4}$, where $\eta = 4\beta -\gamma -3$ and both $\gamma$ and $\beta$ are parametrized post-Newtonian (PPN) parameters. The PPN parameter $\beta$ is determined to be $\beta - 1 = (1.2 \pm 1.1) \times 10ˆ{-4}$. Focusing on the tests of the EP, we discuss the existing data, and characterize the modeling and data analysis techniques. The robustness of the LLR solutions is demonstrated with several different approaches that are presented in the text. We emphasize that near-term improvements in the LLR ranging accuracy will further advance the research of relativistic gravity in the solar system, and, most notably, will continue to provide highly accurate tests of the Equivalence Principle.

#### Jan 09, 2009

0507083 (/preprints/gr-qc)
2009-01-09, 12:12 

## [0812.4870] Gravitational wave burst search in the Virgo C7 data

Authors: The Virgo Collaboration: F. Acernese, et al

Date: 29 Dec 2008

Abstract: A search for gravitational wave burst events has been performed with the Virgo C7 commissioning run data that have been acquired in September 2005 over five days. It focused on un-modeled short duration signals in the frequency range 150 Hz to 2 kHz. A search aimed at detecting the GW emission from the merger and ringdown phases of binary black hole coalescences was also carried out. An extensive understanding of the data was required to be able to handle a burst search using the output of only one detector. A 90% confidence level upper limit on the number of expected events given the Virgo C7 sensitivity curve has been derived as a function of the signal strength, for un-modeled gravitational wave search. The sensitivity of the analysis presented is, in terms of the root sum square strain amplitude, $h_{rss} \simeq 10ˆ{-20} / \sqrt{Hz}$. This can be interpreted in terms of a frequentist upper limit on the rate ${\cal{R}}_{90%}$ of detectable gravitational wave bursts at the level of 1.1 events per day at 90% confidence level. From the binary black hole search, we obtained the distance reach at 50% and 90% efficiency as a function of the total mass of the final black hole. The maximal detection distance for non-spinning high and equal mass black hole binary system obtained by this analysis in C7 data is $\simeq$ 2.9 $\pm$ 0.1 Mpc for a detection efficiency of 50% for a binary of total mass $80 M_{\odot}$.

#### Jan 09, 2009

0812.4870 (/preprints)
2009-01-09, 12:12 

## [0901.0302] Search for Gravitational Waves from Low Mass Binary Coalescences in the First Year of LIGO's S5 Data

Authors: LIGO Scientific Collaboration

Date: 5 Jan 2009

Abstract: We have searched for gravitational waves from coalescing low mass compact binary systems with a total mass between 2 and 35 Msun and a minimum component mass of 1 Msun using data from the first year of the fifth science run (S5) of the three LIGO detectors, operating at design sensitivity. Depending on mass, we are sensitive to coalescences as far as 150 Mpc from the Earth. No gravitational wave signals were observed above the expected background. Assuming a compact binary objects population with a Gaussian mass distribution representing binary neutron star systems, black hole-neutron star binary systems, and binary black hole systems, we calculate the 90%-confidence upper limit on the rate of coalescences to be 3.8 \times 10ˆ{-2} yrˆ{-1} L_{10}ˆ{-1}, 1.6 \times 10ˆ{-2} yrˆ{-1} L_{10}ˆ{-1}, and 2.2 \times 10ˆ{-3} yrˆ{-1} L_{10}ˆ{-1} respectively, where $L_{10}$ is $10ˆ{10}$ times the blue solar luminosity. We also set improved upper limits on the rate of compact binary coalescences per unit blue-light luminosity, as a function of mass.

#### Jan 09, 2009

0901.0302 (/preprints)
2009-01-09, 12:11 

## [0806.2125] An Atomic Gravitational Wave Interferometric Sensor (AGIS)

Authors: Savas Dimopoulos, Peter W. Graham, Jason M. Hogan, Mark A. Kasevich, Surjeet Rajendran

Date: 12 Jun 2008

Abstract: We propose two distinct atom interferometer gravitational wave detectors, one terrestrial and another satellite-based, utilizing the core technology of the Stanford 10 m atom interferometer presently under construction. Each configuration compares two widely separated atom interferometers run using common lasers. The signal scales with the distance between the interferometers, which can be large since only the light travels over this distance, not the atoms. The terrestrial experiment with baseline ~1 km can operate with strain sensitivity ~10ˆ(-19) / Hzˆ(½) in the 1 Hz - 10 Hz band, inaccessible to LIGO, and can detect gravitational waves from solar mass binaries out to megaparsec distances. The satellite experiment with baseline ~1000 km can probe the same frequency spectrum as LISA with comparable strain sensitivity ~10ˆ(-20) / Hzˆ(½). The use of ballistic atoms (instead of mirrors) as inertial test masses improves systematics coming from vibrations, acceleration noise, and significantly reduces spacecraft control requirements. We analyze the backgrounds in this configuration and discuss methods for controlling them to the required levels.

#### Jan 09, 2009

0806.2125 (/preprints)
2009-01-09, 12:06 

## [0901.0993] Numerical black hole initial data with low eccentricity based on post-Newtonian orbital parameters

Authors: Benny Walther, Bernd Bruegmann, Doreen Mueller

Date: 8 Jan 2009

Abstract: Black hole binaries on non-eccentric orbits form an important subclass of gravitational wave sources, but it is a non-trivial issue to construct numerical initial data with minimal initial eccentricity for numerical simulations. We compute post-Newtonian orbital parameters for quasi-spherical orbits using the method of Buonanno, Chen and Damour (2006) and examine the resulting eccentricity in numerical simulations. Four different methods are studied resulting from the choice of Taylor-expanded or effective-one-body Hamiltonians, and from two choices for the energy flux. The eccentricity increases for unequal masses and for spinning black holes, but remains smaller than that obtained from previous post-Newtonian approaches. The effective-one-body Hamiltonian offers advantages for decreasing initial separation as expected, but in the context of this study also performs significantly better than the Taylor-expanded Hamiltonian for binaries with spin.

#### Jan 09, 2009

0901.0993 (/preprints)
2009-01-09, 12:05