## [0709.3839] Estimating the final spin of a binary black hole coalescence

Authors: Alessandra Buonanno, Lawrence E. Kidder, Luis Lehner

Date: 24 Sep 2007

Abstract: We present a straightforward approach for estimating the final black hole spin of a binary black hole coalescence with arbitrary initial masses and spins. Making some simple assumptions, we estimate the final angular momentum to be the sum of the individual spins plus the orbital angular momentum of a test particle orbiting at the last stable orbit around a Kerr black hole with a spin parameter of the final black hole. The formula we obtain is able to reproduce with reasonable accuracy the results from available numerical simulations, but, more importantly, it can be used to investigate what configurations might give rise to interesting dynamics. In particular, we discuss scenarios which might give rise to a ‘flip’ in the direction of the total angular momentum of the system. By studying the dependence of the final spin upon the mass ratio and initial spins we find that our simple approach suggests that it is not possible to spin-up a black hole to extremal values through merger scenarios irrespective of the mass ratio of the objects involved.

#### Sep 27, 2007

0709.3839 (/preprints)
2007-09-27, 16:56 

## [0709.3895] Energy Extraction from Black Holes

Authors: Norbert Straumann

Date: 25 Sep 2007

Abstract: In this lecture I give an introduction to the rotational energy extraction of black holes by the electromagnetic Blandford-Znajek process and the generation of relativistic jets. After some basic material on the electrodynamics of black hole magnetospheres, we derive the most important results of Blandford and Znajek by making use of Kerr-Schild coordinates, which are regular on the horizon. In a final part we briefly describe results of recent numerical simulations of accretion flows on rotating black holes, the resulting large-scale outflows, and the formation of collimated relativistic jets with high Lorentz factors.

#### Sep 27, 2007

0709.3895 (/preprints)
2007-09-27, 16:56 

## [0709.3559] Implementation of standard testbeds for numerical relativity

Authors: M. C. Babiuc, S. Husa, I. Hinder, C. Lechner, E. Schnetter, B. Szilagyi, Y. Zlochower, N. Dorband, D. Pollney, J. Winicour

Date: 22 Sep 2007

Abstract: We sharpen our discussion of the design and implementation of the initial round of testbeds for numerical relativity which was presented in the first paper of the Apples with Apples Alliance. We present benchmark results for various codes which provide templates for analyzing the testbeds and to draw conclusions about various features of the codes. This allows us to sharpen the initial test specifications and add theoretical insight.

#### Sep 25, 2007

0709.3559 (/preprints)
2007-09-25, 17:14 

## [0709.2589] A post-Newtonian diagnosis of quasiequilibrium configurations of neutron star-neutron star and neutron star-black hole binaries

Authors: Emanuele Berti, Sai Iyer, Clifford M. Will

Date: 17 Sep 2007

Abstract: We use a post-Newtonian diagnostic tool to examine numerically generated quasiequilibrium initial data sets for non-spinning double neutron star and neutron star-black hole binary systems. The PN equations include the effects of tidal interactions, parametrized by the compactness of the neutron stars and by suitable values of ‘apsidal’ constants, which measure the degree of distortion of stars subjected to tidal forces. We find that the post-Newtonian diagnostic agrees well with the double neutron star initial data, typically to better than half a percent except where tidal distortions are becoming extreme. We show that the differences could be interpreted as representing small residual eccentricity in the initial orbits. In comparing the diagnostic with preliminary numerical data on neutron star-black hole binaries, we find less agreement.

#### Sep 25, 2007

0709.2589 (/preprints)
2007-09-25, 17:12 

## [0709.1915] Constraining neutron star tidal Love numbers with gravitational wave detectors

Authors: Eanna E. Flanagan, Tanja Hinderer

Date: 12 Sep 2007

Abstract: We quantify the ability of ground-based gravitational wave detectors to constrain the nuclear equation of state using the early, low frequency portion of the signal of detected neutron star - neutron star (NS-NS) inspirals. In this early adiabatic regime, the influence of a NS's internal structure on the phase of the waveform depends only on a single parameter lambda of the star related to its tidal Love number, namely the ratio of the induced quadrupole moment to the perturbing tidal gravitational field. We restrict attention to gravitational wave frequencies smaller than a cutoff frequency of 400 Hz. In this domain, f-mode frequency dependent corrections to the internal-structure signal are less than 3%, and higher order multipole corrections are less than 5%, for NS models with f-mode frequencies greater than 1 kHz. For an inspiral of two non-spinning 1.4 solar mass NSs at a signal-to-noise ratio of 20, LIGO I (LIGO II) detectors will be able to constrain lambda to lambda < 1.3 (3.3) 10ˆ(37) g cmˆ2 sˆ2 with 90% confidence. Fully relativistic NS models show that the corresponding constraint on radius for LIGO I would be R < 12.5 km (14.1 km) for a n=0.5 (n=1.0) polytrope, for 1.4 solar mass NSs.

#### Sep 25, 2007

0709.1915 (/preprints)
2007-09-25, 17:10 

## [0709.2160] High-spin binary black hole mergers

Authors: Pedro Marronetti (1), Wolfgang Tichy (1), Bernd Br&#xfc;gmann (2), Jose Gonz&#xe1;lez (2), Ulrich Sperhake (2) ((1) Florida Atlantic University, (2) University of Jena)

Date: 13 Sep 2007

Abstract: We study identical mass black hole binaries with spins perpendicular to the binary's orbital plane. These binaries have individual spins ranging from $s/mˆ2=-0.90$ to 0.90, ($s_1 = s_2$ in all cases) which is near the limit possible with standard Bowen-York puncture initial data. The extreme cases correspond to the largest initial spin simulations to date. Our results expand the parameter space covered by Rezzolla {\it et al.} and, when combining both data sets, we obtain estimations for the minimum and maximum values for the intrinsic angular momenta of the remnant of binary black hole mergers of $J/Mˆ2=0.341 \pm 0.004$ and $0.951 \pm 0.004$ respectively.

#### Sep 25, 2007

0709.2160 (/preprints)
2007-09-25, 17:10 

## [0709.1139] Cosmic String Detection via Microlensing of Stars

Authors: David F. Chernoff, S.-H. Henry Tye

Date: 7 Sep 2007

Abstract: Cosmic superstrings are produced towards the end of the brane inflation. If the string tension is low enough, loops tend to be relatively long-lived. The resultant string network is expected to contain many loops which are smaller than typical Galactic scales. Cosmic expansion damps the center of mass motion of the loops which then cluster like cold dark matter. Loops will lens stars within the galaxy and local group. We explore microlensing of stars as a tool to detect and to characterize some of the fundamental string and string network properties, including the dimensionless string tension $G \mu/cˆ2$ and the density of string loops within the Galaxy. As $G \mu \to 0$ the intrinsic microlensing rate diverges as $1/\sqrt{G \mu}$ but experimental detection will be limited by shortness of the lensing timescale and/or smallness of the bending angle which each vary $\propto G \mu$. We find that detection is feasible for a range of tensions. As an illustration, the planned optical astrometric survey mission, Gaia, should be able to detect numerous microlensing events for string networks with tensions $10ˆ{-10} \simless G \mu \simless 10ˆ{-6}$. A null result for optical microlensing implies $G \mu \simless 10ˆ{-10}$. If lensing of a given source is observed it will repeat because the internal motions of the loop are relativistic but the center of mass motion may be much smaller, of order the halo velocity. This distinctive hallmark $\sim 1000$ repetitions, suggests a useful method for confirmation of a potential lensing detection.

#### Sep 11, 2007

0709.1139 (/preprints)
2007-09-11, 09:45 

## [0709.1050] A template bank to search for gravitational waves from inspiralling compact binaries: II. Phenomenological model

Authors: Thomas Cokelaer

Date: 7 Sep 2007

Abstract: Matched filtering is used to search for gravitational waves emitted by inspiralling compact binaries in data from ground-based interferometers. One of the key aspects of the detection process is the deployment of a set of templates, also called a template bank, to cover the astrophysically interesting region of the parameter space. In a companion paper, we described the template-bank algorithm used in the analysis of LIGO data to search for signals from non-spinning binaries made of neutron star and/or stellar-mass black holes; this template bank is based upon physical template families. In this paper, we describe the phenomenological template bank that was used to search for gravitational waves from non-spinning black hole binaries (from stellar mass formation) in the second, third and fourth LIGO science runs. We briefly explain the design of the bank, whose templates are based on a phenomenological detection template family. We show that this template bank gives matches greater than 95% with the physical template families that are expected to be captured by the phenomenological templates.

#### Sep 09, 2007

0709.1050 (/preprints)
2007-09-09, 22:12 

## [0709.0940] Coherent network analysis for triggered gravitational wave burst searches

Authors: Kazuhiro Hayama, Soumya D. Mohanty, Malik Rakhmanov, Shantanu Desai

Date: 6 Sep 2007

Abstract: Searches for gravitational wave bursts that are triggered by the observation of astronomical events require a different mode of analysis than all-sky, blind searches. For one, much more prior information is usually available in a triggered search which can and should be used in the analysis. Second, since the data volume is usually small in a triggered search, it is also possible to use computationally more expensive algorithms for tasks such as data pre-processing that can consume significant computing resources in a high data-volume un-triggered search. From the statistical point of view, the reduction in the parameter space search volume leads to higher sensitivity than an un-triggered search. We describe here a data analysis pipeline for triggered searches, called {\tt RIDGE}, and present preliminary results for simulated noise and signals.

#### Sep 07, 2007

0709.0940 (/preprints)
2007-09-07, 13:13 

## [0709.0685] Not Only Because of Theory: Dyson, Eddington and the Competing Myths of the 1919 Eclipse Expedition

Authors: Daniel Kennefick

Date: 5 Sep 2007

Abstract: The 1919 Eclipse Expedition to test the light-bending prediction of General Relativity remains one of the most famous physics experiments of the 20th century. However, in recent decades it has been increasingly often alleged that the data-analysis of the expedition's leaders was faulty and biased in favor of Einstein's theory. Arthur Stanley Eddington is particularly alleged to have been prejudiced in favor of general relativity. Specifically it is claimed that some of the data, which would have favored the so-called Newtonian prediction, was thrown out on dubious grounds. This paper argues that a close examination of the views of the expedition's organizers, and of their data analysis, suggests that they had good grounds for acting as they did, and that the key people involved, in particular the astronomer Frank Watson Dyson, were not biased in favor of Einstein. It also draws attention to a modern re-analysis of the most important eclipse plates which, though overlooked until now, tends to strongly support the thesis of this paper.

#### Sep 05, 2007

0709.0685 (/preprints)
2007-09-05, 22:11 

## [0709.0403] Unstable g-modes in Proto-Neutron Stars

Authors: V. Ferrari, L. Gualtieri, J. A. Pons

Date: 4 Sep 2007

Abstract: In this article we study the possibility that, due to non-linear couplings, unstable g-modes associated to convective motions excite stable oscillating g-modes. This problem is of particular interest, since gravitational waves emitted by a newly born proto-neutron star pulsating in its stable g-modes would be in the bandwidth of VIRGO and LIGO. Our results indicate that nonlinear saturation of unstable modes occurs at relatively low amplitudes, and therefore, even if there exists a coupling between stable and unstable modes, it does not seem to be sufficiently effective to explain, alone, the excitation of the oscillating g-modes found in hydrodynamical simulations.

#### Sep 05, 2007

0709.0403 (/preprints)
2007-09-05, 22:11 

## [0709.0657] Quasi-Normal Modes and Gravitational Wave Astronomy

Authors: V. Ferrari, L. Gualtieri

Date: 5 Sep 2007

Abstract: We review the main results obtained in the literature on quasi-normal modes of compact stars and black holes, in the light of recent exciting developments of gravitational wave detectors. Quasi-normal modes are a fundamental feature of the gravitational signal emitted by compact objects in many astrophysical processes; we will show that their eigenfrequencies encode interesting information on the nature and on the inner structure of the emitting source and we will discuss whether we are ready for a gravitational wave asteroseismology.

#### Sep 05, 2007

0709.0657 (/preprints)
2007-09-05, 22:10 

## [0709.0660] Oscillations of General Relativistic Multi-fluid/Multi-layer Compact Stars

Authors: Lap-Ming Lin, N. Andersson, G. L. Comer

Date: 5 Sep 2007

Abstract: We develop the formalism for determining the quasinormal modes of general relativistic multi-fluid compact stars in such a way that the impact of superfluid gap data can be assessed. Our results represent the first attempt to study true multi-layer dynamics, an important step towards considering realistic superfluid/superconducting compact stars. We combine a relativistic model for entrainment with model equations of state that explicity incorporate the symmetry energy. Our analysis emphasises the many different parameters that are required for this kind of modelling, and the fact that standard tabulated equations of state are grossly incomplete in this respect. To make progress, future equations of state need to provide the energy density as a function of the various nucleon number densities, the temperature (i.e. entropy), and the entrainment among the various components.

#### Sep 05, 2007

0709.0660 (/preprints)
2007-09-05, 22:10 

## [0709.0299] Binary black hole merger: symmetry and the spin expansion

Authors: Latham Boyle, Michael Kesden, Samaya Nissanke

Date: 4 Sep 2007

Abstract: We regard binary black hole (BBH) merger as a map from a simple initial state (two well separated Kerr black holes, with dimensionless spins {\bf a} and {\bf b}) to a simple final state (a single Kerr black hole with mass m, dimensionless spin {\bf s}, and kick velocity {\bf k}). By Taylor expanding this map around {\bf a} = {\bf b} = 0 and systematically applying symmetry constraints, we obtain a formalism that is simple, yet remarkably successful at explaining existing BBH simulations. Our formalism also makes a host of detailed quantitative predictions for future BBH simulations, and suggests a much more efficient way of mapping out the parameter space of BBH mergers. Since we rely on symmetry rather than dynamics, our expansion remains valid through all stages of the merger (inspiral, plunge, ringdown), and hence complements previous analytical techniques like the post-Newtonian approximation.

#### Sep 05, 2007

0709.0299 (/preprints)
2007-09-05, 08:49 

## [0708.4202] Gravitational waves from black-hole mergers

Authors: John G. Baker, William D. Boggs, Joan M. Centrella, Bernard J. Kelly, Sean T. McWilliams, James R. van Meter

Date: 30 Aug 2007

Abstract: Coalescing black-hole binaries are expected to be the strongest sources of gravitational waves for ground-based interferometers as well as the space-based interferometer LISA. Recent progress in numerical relativity now makes it possible to calculate the waveforms from the strong-field dynamical merger and is revolutionizing our understanding of these systems. We review these dramatic developments, emphasizing applications to issues in gravitational wave observations. These new capabilities also make possible accurate calculations of the recoil or kick imparted to the final remnant black hole when the merging components have unequal masses, or unequal or unaligned spins. We highlight recent work in this area, focusing on results of interest to astrophysics.

#### Sep 02, 2007

0708.4202 (/preprints)
2007-09-02, 22:14 

## [0708.4242] Gaussianity of LISA's confusion backgrounds

Authors: Etienne Racine, Curt Cutler

Date: 30 Aug 2007

Abstract: Data analysis for the proposed Laser Interferometer Space Antenna (LISA) will be complicated by the huge number of sources in the LISA band. Throughout much of the band, galactic white dwarf binaries (GWDBs) are sufficiently dense in frequency space that it will be impossible to resolve most of them, and "confusion noise" from the unresolved Galactic binaries will dominate over instrumental noise in determining LISA's sensitivity to other sources in that band. Confusion noise from unresolved extreme-mass-ratio inspirals (EMRIs) could also contribute significantly to LISA's total noise curve. To date, estimates of the effect of LISA's confusion noise on matched-filter searches and their detection thresholds have generally approximated the noise as Gaussian, based on the Central Limit Theorem. However in matched-filter searches, the appropriate detection threshold for a given class of signals may be located rather far out on the tail of the signal-to-noise probability distribution, where a priori it is unclear whether the Gaussian approximation is reliable. Using the Edgeworth expansion and the theory of large deviations, we investigate the probability distribution of the usual matched-filter detection statistic, far out on the tail of the distribution. We apply these tools to four somewhat idealized versions of specific LISA searches.

#### Sep 02, 2007

0708.4242 (/preprints)
2007-09-02, 22:13