**Authors**: Matthew Kerr

**Date**: 31 Jan 2011

**Abstract**: The sensitivity of the Large Area Telescope (LAT) aboard the Fermi Gamma-ray Space Telescope allows detection of thousands of new gamma-ray sources and detailed characterization of the spectra and variability of bright sources. Unsurprisingly, this increased capability leads to increased complexity in data analysis. Likelihood methods are ideal for connecting models with data, but the computational cost of folding the model input through the multi-scale instrument response function is appreciable. Both interactive analysis and large projects — such as analysis of the full gamma-ray sky — can be prohibitive or impossible, reducing the scope of the science possible with the LAT. To improve on this situation, we have developed pointlike, a software package for fast maximum likelihood analysis of LAT data. It is interactive by design and its rapid evaluation of the likelihood facilitates exploratory and large-scale, all-sky analysis. We detail its implementation and validate its performance on simulated data. We demonstrate its capability for interactive analysis and present several all-sky analyses. These include a search for new gamma-ray sources and the selection of LAT sources with pulsar-like characteristics for targeted radio pulsation searches. We conclude by developing sensitive periodicity tests incorporating spectral information obtained from pointlike.

1101.6072
(/preprints)

2011-01-31, 22:25
**[edit]**

**Authors**: C. Skordis, T.G. Zlosnik

**Date**: 31 Jan 2011

**Abstract**: Modified Newtonian Dynamics is an empirical modification to Poisson's equation which has had success in accounting for the ‘gravitational field’ $\Phi$ in a variety of astrophysical systems. The field $\Phi$ may be interpreted in terms of the weak field limit of a variety of spacetime geometries. Here we consider three of these geometries in a more comprehensive manner and look at the effect on timelike and null geodesics. In particular we consider the Aquadratic Lagrangian (AQUAL) theory, Tensor-Vector-Scalar (TeVeS) theory and Generalized Einstein-{\AE}ther (GEA) theory. We uncover a number of novel features, some of which are specific to the theory considered while others are generic. In the case of AQUAL and TeVeS theories, the spacetime exhibits an excess (AQUAL) or deficit (TeVeS) solid angle akin to the case of a Barriola-Vilenkin global monopole. In the case of GEA, a disformal symmetry of the action emerges in the limit of $\grad\Phi\rightarrow 0$. Finally, in all theories studied, massive particles can never reach spatial infinity while photons can do so only after experiencing infinite redshift.

1101.6019
(/preprints)

2011-01-31, 22:25
**[edit]**

**Authors**: Adam Rogers, Jason D. Fiege

**Date**: 30 Jan 2011

**Abstract**: Strong gravitational lensing of an extended object is described by a mapping from source to image coordinates that is nonlinear and cannot generally be inverted analytically. Determining the structure of the source intensity distribution also requires a description of the blurring effect due to a point spread function. This initial study uses an iterative gravitational lens modeling scheme based on the semilinear method to determine the linear parameters (source intensity profile) of a strongly lensed system. Our 'matrix-free' approach avoids construction of the lens and blurring operators while retaining the least squares formulation of the problem. The parameters of an analytical lens model are found through nonlinear optimization by an advanced genetic algorithm (GA) and particle swarm optimizer (PSO). These global optimization routines are designed to explore the parameter space thoroughly, mapping model degeneracies in detail. We develop a novel method that determines the L-curve for each solution automatically, which represents the trade-off between the image chi-square and regularization effects, and allows an estimate of the optimally regularized solution for each lens parameter set. In the final step of the optimization procedure, the lens model with the lowest chi-square is used while the global optimizer solves for the source intensity distribution directly. This allows us to accurately determine the number of degrees of freedom in the problem to facilitate comparison between lens models and enforce positivity on the source profile. In practice we find that the GA conducts a more thorough search of the parameter space than the PSO.

1101.5803
(/preprints)

2011-01-31, 22:25
**[edit]**

**Authors**: Luciano Rezzolla, Bruno Giacomazzo, Luca Baiotti, Jonathan Granot, Chryssa Kouveliotou, Miguel A. Aloy

**Date**: 22 Jan 2011

**Abstract**: Short Gamma-Ray Bursts (SGRBs) are among the most luminous explosions in the universe, releasing in less than one second the energy emitted by our Galaxy over one year. Despite decades of observations, the nature of their "central-engine" remains unknown. Considering a generic binary of magnetized neutron stars and solving Einstein equations, we show that their merger results in a rapidly spinning black hole surrounded by a hot and highly magnetized torus. Lasting over 35 ms and much longer than previous simulations, our study reveals that magnetohydrodynamical instabilities amplify an initially turbulent magnetic field of ~ 10ˆ{12} G to produce an ordered poloidal field of ~ 10ˆ{15} G along the black-hole spin-axis, within a half-opening angle of ~ 30 deg, which may naturally launch a relativistic jet. The broad consistency of our ab-initio calculations with SGRB observations shows that the merger of magnetized neutron stars can provide the basic physical conditions for the central-engine of SGRBs.

1101.4298
(/preprints)

2011-01-31, 22:25
**[edit]**

**Authors**: R. Smits, S.J. Tingay, N. Wex, M. Kramer, B. Stappers

**Date**: 31 Jan 2011

**Abstract**: Parallax measurements of pulsars allow for accurate measurements of the interstellar electron density and contribute to accurate tests of general relativity using binary systems. The Square Kilometre Array (SKA) will be an ideal instrument for measuring the parallax of pulsars, having a very high sensitivity as well as baselines extending up to several thousands of kilometres. We have performed simulations to estimate the number of pulsars for which the parallax can be measured with the SKA and to what distance a parallax can be measured. We compare two different methods. The first method measures the parallax directly by utilising the long baselines of the SKA to form high angular resolution images. The second method uses the arrival times of the radio signals of pulsars to fit a transformation between time coordinates in the terrestrial frame and the comoving pulsar frame which directly yields the parallax. We find that with the first method a parallax with an accuracy of 20% or less can be measured up to a maximum distance of 13 kpc, which would include 9,000 pulsars. By timing pulsars with the most stable arrival times for the radio emission, parallaxes can be measured for about 3,600 millisecond pulsars up to a distance of 9 kpc with an accuracy of 20%.

1101.5971
(/preprints)

2011-01-31, 22:25
**[edit]**

**Authors**: S. Klimenko, G. Vedovato, M. Drago, G. Mazzolo, G. Mitselmakher, C. Pankow, G. Prodi, V. Re, F. Salemi, I. Yakushin

**Date**: 27 Jan 2011

**Abstract**: Coincident observations with gravitational wave (GW) detectors and other astronomical instruments are in the focus of the experiments with the network of LIGO, Virgo and GEO detectors. They will become a necessary part of the future GW astronomy as the next generation of advanced detectors comes online. The success of such joint observations directly depends on the source localization capabilities of the GW detectors. In this paper we present studies of the sky localization of transient sources with the future advanced detector networks and describe their fundamental properties. By reconstructing sky coordinates of ad hoc signals injected into simulated detector noise we study the accuracy of the source localization and its dependence on the strength of injected signals, waveforms and network configurations.

1101.5408
(/preprints)

2011-01-31, 13:31
**[edit]**

**Authors**: S. Capozziello, M. De Laurentis, I. De Martino, M. Formisano, D. Vernieri

**Date**: 27 Jan 2011

**Abstract**: We discuss the possibility to obtain an electromagnetic emission accompanying the gravitational waves emitted in the coalescence of a compact binary system. Motivated by the existence of black hole configurations with open magnetic field lines along the rotation axis, we consider a magnetic dipole in the system, the evolution of which leads to (i) electromagnetic radiation, and (ii) a contribution to the gravitational radiation, the luminosity of both being evaluated. Starting from the observations on magnetars, we impose upper limits for both the electromagnetic emission and the contribution of the magnetic dipole to the gravitational wave emission. Adopting this model for the evolution of neutron star binaries leading to short gamma ray bursts, we compare the correction originated by the electromagnetic field to the gravitational waves emission, finding that they are comparable for particular values of the magnetic field and of the orbital radius of the binary system. Finally we calculate the electromagnetic and gravitational wave energy outputs which result comparable for some values of magnetic field and radius.

1101.5306
(/preprints)

2011-01-28, 09:03
**[edit]**

**Authors**: Justin M. Brown (1), Mukremin Kilic (2), Warren R. Brown (2), Scott J. Kenyon (3) ((1) Franklin and Marshall College (2) Smithsonian Astrophysical Observatory)

**Date**: 26 Jan 2011

**Abstract**: We describe spectroscopic observations of 21 low-mass (<0.45 M_sun) white dwarfs (WDs) from the Palomar-Green Survey obtained over four years. We use both radial velocities and infrared photometry to identify binary systems, and find that the fraction of single, low-mass WDs is <30%. We discuss the potential formation channels for these single stars including binary mergers of lower-mass objects. However, binary mergers are not likely to explain the observed number of single low-mass WDs. Thus additional formation channels, such as enhanced mass loss due to winds or interactions with substellar companions, are likely.

1101.5169
(/preprints)

2011-01-28, 09:03
**[edit]**

**Authors**: Kent Yagi, Norihiro Tanahashi, Takahiro Tanaka

**Date**: 26 Jan 2011

**Abstract**: In Randall-Sundrum II (RS-II) braneworld model, it has been conjectured according to the AdS/CFT correspondence that brane-localized black hole (BH) larger than the bulk AdS curvature scale $\ell$ cannot be static, and it is dual to a four dimensional BH emitting the Hawking radiation through some quantum fields. In this scenario, the number of the quantum field species is so large that this radiation changes the orbital evolution of a BH binary. We derived the correction to the gravitational waveform phase due to this effect and estimated the upper bounds on $\ell$ by performing Fisher analyses. We found that DECIGO/BBO can put a stronger constraint than the current table-top result by detecting gravitational waves from small mass BH/BH and BH/neutron star (NS) binaries. Furthermore, DECIGO/BBO is expected to detect 10$ˆ5$ BH/NS binaries per year. Taking this advantage, we found that DECIGO/BBO can actually measure $\ell$ down to $\ell=0.33 \mu$m for 5 year observation if we know that binaries are circular a priori. This is about 40 times smaller than the upper bound obtained from the table-top experiment. On the other hand, when we take eccentricities into binary parameters, the detection limit weakens to $\ell=1.5 \mu$m due to strong degeneracies between $\ell$ and eccentricities. We also derived the upper bound on $\ell$ from the expected detection number of extreme mass ratio inspirals (EMRIs) with LISA and BH/NS binaries with DECIGO/BBO, extending the discussion made recently by McWilliams. We found that these less robust constraints are weaker than the ones from phase differences.

1101.4997
(/preprints)

2011-01-26, 18:37
**[edit]**

**Authors**: Kipp Cannon, Chad Hanna, Drew Keppel

**Date**: 25 Jan 2011

**Abstract**: Gravitational-wave searches for the merger of compact binaries use matched-filtering as the method of detecting signals and estimating parameters. Such searches construct a fine mesh of filters covering a signal parameter space at high density. Previously it has been shown that singular value decomposition can reduce the effective number of filters required to search the data. Here we study how the basis provided by the singular value decomposition changes dimension as a function of template bank density. We will demonstrate that it is sufficient to use the basis provided by the singular value decomposition of a low density bank to accurately reconstruct arbitrary points within the boundaries of the template bank. Since this technique is purely numerical it may have applications to interpolating the space of numerical relativity waveforms.

1101.4939
(/preprints)

2011-01-26, 18:37
**[edit]**

**Authors**: Bruny Baret, Imre Bartos, Boutayeb Bouhou, Alessandra Corsi, Irene Di Palma, Corinne Donzaud, Véronique Van Elewyck, Chad Finley, Gareth Jones, Antoine Kouchner, Szabolcs Màrka, Zsuzsa Màrka, Luciano Moscoso, Eric Chassande-Mottin, Maria Alessandra Papa, Thierry Pradier, Peter Raffai, Jameson Rollins, Patrick Sutton

**Date**: 24 Jan 2011

**Abstract**: We derive a conservative coincidence time window for joint searches of gravita-tional-wave (GW) transients and high-energy neutrinos (HENs, with energies above 100GeV), emitted by gamma-ray bursts (GRBs). The last are among the most interesting astrophysical sources for coincident detections with current and near-future detectors. We take into account a broad range of emission mechanisms. We take the upper limit of GRB durations as the 95% quantile of the T90's of GRBs observed by BATSE, obtaining a GRB duration upper limit of ~150s. Using published results on high-energy (>100MeV) photon light curves for 8 GRBs detected by Fermi LAT, we verify that most high-energy photons are expected to be observed within the first ~150s of the GRB. Taking into account the breakout-time of the relativistic jet produced by the central engine, we allow GW and HEN emission to begin up to 100s before the onset of observable gamma photon production. Using published precursor time differences, we calculate a time upper bound for precursor activity, obtaining that 95% of precursors occur within ~250s prior to the onset of the GRB. Taking the above different processes into account, we arrive at a time window of tHEN - tGW ~ [-500s,+500s]. Considering the above processes, an upper bound can also be determined for the expected time window of GW and/or HEN signals coincident with a detected GRB, tGW - tGRB ~ tHEN - tGRB ~ [-350s,+150s].

1101.4669
(/preprints)

2011-01-26, 16:15
**[edit]**

**Authors**: Massimo Tinto

**Date**: 20 Jan 2011

**Abstract**: We estimate the sensitivity to nano-Hertz gravitational waves of pulsar timing experiments in which two highly-stable millisecond pulsars are tracked simultaneously with two neighboring radio telescopes that are referenced to the same time-keeping subsystem (i.e. "the clock"). By taking the difference of the two time-of-arrival residual data streams we can exactly cancel the clock noise in the combined data set, thereby enhancing the sensitivity to gravitational waves. We estimate that, in the band ($10ˆ{-9} - 10ˆ{-8}$) Hz, this "interferometric" pulsar timing technique can potentially improve the sensitivity to gravitational radiation by almost two orders of magnitude over that of single-telescopes. Interferometric pulsar timing experiments could be performed with neighboring pairs of antennas of the forthcoming large arraying projects.

1101.3990
(/preprints)

2011-01-26, 16:14
**[edit]**

**Authors**: Tanja Bode, Tamara Bogdanovic, Roland Haas, James Healy, Pablo Laguna, Deirdre Shoemaker

**Date**: 24 Jan 2011

**Abstract**: Modeling the late inspiral and merger of supermassive black holes is central to understanding accretion processes and the conditions under which electromagnetic emission accompanies gravitational waves. We use fully general relativistic, hydrodynamics simulations to investigate how electromagnetic signatures correlate with black hole spins, mass ratios, and the gaseous environment in this final phase of binary evolution. In all scenarios, we find some form of characteristic electromagnetic variability whose pattern depends on the spins and binary mass ratios. Binaries in hot accretion flows exhibit a flare followed by a sudden drop in luminosity associated with the plunge and merger, as well as quasi-periodic oscillations correlated with the gravitational waves during the inspiral. Conversely, circumbinary disk systems are characterized by a low luminosity of variable emission, suggesting challenging prospects for their detection.

1101.4684
(/preprints)

2011-01-26, 16:14
**[edit]**

**Authors**: John Kormendy, Ralf Bender

**Date**: 24 Jan 2011

**Abstract**: Supermassive black holes have been detected in all galaxies that contain bulge components when the galaxies observed were close enough so that the searches were feasible. Together with the observation that bigger black holes live in bigger bulges, this has led to the belief that black hole growth and bulge formation regulate each other. That is, black holes and bulges "coevolve". Therefore, reports of a similar correlation between black holes and the dark matter halos in which visible galaxies are embedded have profound implications. Dark matter is likely to be nonbaryonic, so these reports suggest that unknown, exotic physics controls black hole growth. Here we show - based in part on recent measurements of bulgeless galaxies - that there is almost no correlation between dark matter and parameters that measure black holes unless the galaxy also contains a bulge. We conclude that black holes do not correlate directly with dark matter. They do not correlate with galaxy disks, either. Therefore black holes coevolve only with bulges. This simplifies the puzzle of their coevolution by focusing attention on purely baryonic processes in the galaxy mergers that make bulges.

1101.4650
(/preprints)

2011-01-26, 16:14
**[edit]**

**Authors**: Kent Yagi, Naoki Seto

**Date**: 20 Jan 2011

**Abstract**: The primary target for the planned space-borne gravitational wave interferometers DECIGO/BBO is a primordial gravitational wave background (PGWB). However there exist astrophysical foregrounds and among them, gravitational waves from neutron star (NS) binaries are the solid and strong component that must be identified and subtracted. In this paper, we discuss the geometry of detector configurations preferable for identifying the NS/NS binary signals. As a first step, we analytically estimate the minimum signal-to-noise ratios (SNRs) of the binaries for several static detector configurations that are characterized by adjustable geometrical parameters, and determine the optimal values for these parameters. Next we perform numerical simulations to take into account the effect of detector motions, and find reasonable agreements with the analytical results. We show that, with the standard network formed by 4 units of triangle detectors, the proposed BBO sensitivity would be sufficient in receiving gravitational waves from all the NS/NS binaries at $z\le 5$ with SNRs higher than 25. We also discuss the minimum sensitivity of DECIGO required for the foreground identification.

1101.3940
(/preprints)

2011-01-26, 16:14
**[edit]**

**Authors**: Michael Kesden

**Date**: 19 Jan 2011

**Abstract**: A test particle of mass mu on a bound geodesic of a Kerr black hole of mass M >> mu will slowly inspiral as gravitational radiation extracts energy and angular momentum from its orbit. This inspiral can be considered adiabatic when the orbital period is much shorter than the timescale on which energy is radiated, and quasi-circular when the radial velocity is much less than the azimuthal velocity. Although the inspiral always remains adiabatic provided mu << M, the quasi-circular approximation breaks down as the particle approaches the innermost stable circular orbit (ISCO). In this paper, we relax the quasi-circular approximation and solve the radial equation of motion explicitly near the ISCO. We use the requirement that the test particle's 4-velocity remain properly normalized to calculate a new contribution to the difference between its energy and angular momentum. This difference determines how a black hole's spin changes following a test-particle merger, and can be extrapolated to help predict the mass and spin of the final black hole produced in finite-mass-ratio black-hole mergers. Our new contribution is particularly important for nearly maximally spinning black holes, as it can affect whether a merger produces a naked singularity.

1101.3749
(/preprints)

2011-01-20, 09:24
**[edit]**

**Authors**: Scott E. Field, Chad R. Galley, Frank Herrmann, Jan S. Hesthaven, Evan Ochsner, Manuel Tiglio

**Date**: 19 Jan 2011

**Abstract**: We introduce a reduced basis approach as a new paradigm for modeling, representing and searching for gravitational waves. We construct waveform catalogs for non-spinning compact binary coalescences, and we find that for accuracies of $99\%$ and $99.999\%$ the method generates a factor of about $10-10ˆ5$ fewer templates than standard placement methods. The continuum of gravitational waves can be represented by a finite and comparatively compact basis. The method is robust under variations in the noise of detectors, implying that only a single catalog needs to be generated.

1101.3765
(/preprints)

2011-01-20, 09:23
**[edit]**

**Authors**: Fredrick A. Jenet, J.W. Armstrong, Massimo Tinto

**Date**: 19 Jan 2011

**Abstract**: At nanohertz frequencies gravitational waves (GWs) cause variations in time-of-arrival of pulsar signals potentially measurable via precision timing observations. Here we compute very-low-frequency GW sensitivity constrained by instrumental, propagation, and other noises fundamentally limiting pulsar timing observations. Reaching expected GW signal strengths will require estimation and removal of $\simeq$99% of time-of-arrival fluctuations caused by typical interstellar plasma turbulence and a reduction of white rms timing noise to $\sim$100 nsec or less. If these were achieved, single-pulsar signal-to-noise ratio (SNR) = 1 sensitivity is then limited by the best current terrestrial time standards at $h_{rms} \sim$2 $\times 10ˆ{-16}$ [f/(1 cycle/year)]$ˆ{-½}$ for $f < 3 \times 10ˆ{-8}$ Hz, where f is Fourier frequency and a bandwidth of 1 cycle/(10 years) is assumed. This sensitivity envelope may be optimistic in that it assumes negligible intrinsic pulsar rotational noise, perfect time transfer from time standard to observatory, and stable pulse profiles. Nonetheless it can be compared to predicted signal levels for a broadband astrophysical GW background from supermassive black hole binaries. Such a background is comparable to timekeeping-noise only for frequencies lower than about 1 cycle/(10 years), indicating that reliable detections will require substantial improvements in signal-to-noise ratio through pulsar array signal processing.

1101.3759
(/preprints)

2011-01-20, 09:23
**[edit]**

**Authors**: Leor Barack, Norichika Sago

**Date**: 17 Jan 2011

**Abstract**: We study conservative finite-mass corrections to the motion of a particle in a bound (eccentric) strong-field orbit around a Schwarzschild black hole. We assume the particle's mass $\mu$ is much smaller than the black hole mass $M$, and explore post-geodesic corrections of $O(\mu/M)$. Our analysis uses numerical data from a recently developed code that outputs the Lorenz-gauge gravitational self-force (GSF) acting on the particle along the eccentric geodesic. First, we calculate the $O(\mu/M)$ conservative correction to the periastron advance of the orbit, as a function of the (gauge dependent) semi-latus rectum and eccentricity. A gauge-invariant description of the GSF precession effect is made possible in the circular-orbit limit, where we express the correction to the periastron advance as a function of the invariant azimuthal frequency. We compare this relation with results from fully nonlinear numerical-relativistic simulations. In order to obtain a gauge-invariant measure of the GSF effect for fully eccentric orbits, we introduce a suitable generalization of Detweiler's circular-orbit "red shift" invariant. We compute the $O(\mu/M)$ conservative correction to this invariant, expressed as a function of the two invariant frequencies that parametrize the orbit. Our results are in good agreement with results from post-Newtonian calculations in the weak field regime, as we shall report elsewhere. The results of our study can inform the development of analytical models for the dynamics of strongly-gravitating binaries. They also provide an accurate benchmark for future numerical-relativistic simulations.

1101.3331
(/preprints)

2011-01-20, 09:23
**[edit]**

**Authors**: Ryan N. Lang, Scott A. Hughes, Neil J. Cornish

**Date**: 19 Jan 2011

**Abstract**: The future space-based gravitational wave detector LISA will be able to measure parameters of coalescing massive black hole binaries, often to extremely high accuracy. Previous work has demonstrated that the black hole spins can have a strong impact on the accuracy of parameter measurement. Relativistic spin-induced precession modulates the waveform in a manner which can break degeneracies between parameters, in principle significantly improving how well they are measured. Recent studies have indicated, however, that spin precession may be weak for an important subset of astrophysical binary black holes: those in which the spins are aligned due to interactions with gas. In this paper, we examine how well a binary's parameters can be measured when its spins are partially aligned and compare results using waveforms that include higher post-Newtonian harmonics to those that are truncated at leading quadrupole order. We find that the weakened precession can substantially degrade parameter estimation, particularly for the "extrinsic" parameters sky position and distance. Absent higher harmonics, LISA typically localizes the sky position of a nearly aligned binary about an order of magnitude less accurately than one for which the spin orientations are random. Our knowledge of a source's sky position will thus be worst for the gas-rich systems which are most likely to produce electromagnetic counterparts. Fortunately, higher harmonics of the waveform can make up for this degradation. By including harmonics beyond the quadrupole in our waveform model, we find that the accuracy with which most of the binary's parameters are measured can be substantially improved. In some cases, the improvement is such that they are measured almost as well as when the binary spins are randomly aligned.

1101.3591
(/preprints)

2011-01-20, 09:19
**[edit]**

**Authors**: Nora Elisa Chisari, Matias Zaldarriaga

**Date**: 18 Jan 2011

**Abstract**: On large scales, comparable to the horizon, the observable clustering properties of galaxies are affected by various General Relativistic effects. To calculate these effects one needs to consistently solve for the metric, densities and velocities in a specific coordinate system or gauge. The method of choice for simulating large scale structure is numerical N-body simulations which are performed in the Newtonian limit. Even though one might worry that the use of the Newtonian approximation would make it impossible to use these simulations to compute properties on very large scales we show that the simulations are still solving the dynamics correctly even for long modes and give formulas to obtain the position of particles in the Newtonian gauge given the positions computed in the simulation. We also give formulas to convert from the output coordinates of N-body simulations to the observable coordinates of the particles.

1101.3555
(/preprints)

2011-01-20, 09:18
**[edit]**

**Authors**: Christian Knigge (University of Southampton)

**Date**: 14 Jan 2011

**Abstract**: The last few years have seen tremendous progress in our understanding of cataclysmic variable stars. As a result, we are finally developing a much clearer picture of their evolution as binary systems, the physics of the accretion processes powering them, and their relation to other compact accreting objects. In this review, I will highlight some of the most exciting recent breakthroughs. Several of these have opened up completely new avenues of research that will probably lead to additional major advances over the next decade.

1101.2901
(/preprints)

2011-01-18, 12:31
**[edit]**

**Authors**: Tania Regimbau

**Date**: 14 Jan 2011

**Abstract**: A gravitational wave stochastic background of astrophysical origin may have resulted from the superposition of a large number of unresolved sources since the beginning of stellar activity. Its detection would put very strong constrains on the physical properties of compact objects, the initial mass function or the star formation history. On the other hand, it could be a 'noise' that would mask the stochastic background of cosmological origin. We review the main astrophysical processes able to produce a stochastic background and discuss how it may differ from the primordial contribution by its statistical properties. Current detection methods are also presented.

1101.2762
(/preprints)

2011-01-18, 12:31
**[edit]**

**Authors**: P. M. Saz Parkinson (for the Fermi-LAT Collaboration)

**Date**: 16 Jan 2011

**Abstract**: Blind Searches of Fermi Large Area Telescope (LAT) data have resulted in the discovery of 24 gamma-ray pulsars in the first year of survey operations, most of which remain undetected in radio, despite deep radio follow-up searches. I summarize the latest Fermi LAT blind search efforts and results, including the discovery of a new Geminga-like pulsar, PSR J0734-1559. Finally, I discuss some of the challenges faced in carrying out these searches into the future, as well as the prospects for finding additional pulsars among the large number of LAT unassociated sources.

1101.3096
(/preprints)

2011-01-18, 12:31
**[edit]**

**Authors**: Yu.G. Ignatyev

**Date**: 17 Jan 2011

**Abstract**: The effect of an excitation of a gravitational wave (GW) on shock waves in a highly magnetized plasma, GMSW, is studied as an effective means for the detection of GW radiated by neutron stars. It is shown that there is every reason to identify the giant impulses of the pulsar NP 0532 with GMSW.

1101.3242
(/preprints)

2011-01-18, 12:30
**[edit]**

**Authors**: Jeffrey E. McClintock, Ramesh Narayan, Shane W. Davis, Lijun Gou, Akshay Kulkarni, Jerome A. Orosz, Robert F. Penna, Ronald A. Remillard, James F. Steiner

**Date**: 4 Jan 2011

**Abstract**: A typical galaxy is thought to contain tens of millions of stellar-mass black holes, the collapsed remnants of once massive stars, and a single nuclear supermassive black hole. Both classes of black holes accrete gas from their environments. The accreting gas forms a flattened orbiting structure known as an accretion disk. During the past several years, it has become possible to obtain measurements of the spins of the two classes of black holes by modeling the X-ray emission from their accretion disks. Two methods are employed, both of which depend upon identifying the inner radius of the accretion disk with the innermost stable circular orbit (ISCO), whose radius depends only on the mass and spin of the black hole. In the Fe K method, which applies to both classes of black holes, one models the profile of the relativistically-broadened iron line with a special focus on the gravitationally redshifted red wing of the line. In the continuum-fitting method, which has so far only been applied to stellar-mass black holes, one models the thermal X-ray continuum spectrum of the accretion disk. We discuss both methods, with a strong emphasis on the continuum-fitting method and its application to stellar-mass black holes. Spin results for eight stellar-mass black holes are summarized. These data are used to argue that the high spins of at least some of these black holes are natal, and that the presence or absence of relativistic jets in accreting black holes is not entirely determined by the spin of the black hole.

1101.0811
(/preprints)

2011-01-18, 12:30
**[edit]**

**Authors**: Nicolas Yunes, Leo C. Stein

**Date**: 14 Jan 2011

**Abstract**: We study two large classes of alternative theories, modifying the action through algebraic, quadratic curvature invariants coupled to scalar fields. We find one class that admits solutions that solve the vacuum Einstein equations and another that does not. In the latter, we find a deformation to the Schwarzschild metric that solves the modified field equations in the small coupling approximation. We calculate the event horizon shift, the innermost stable circular orbit shift, and corrections to gravitational waves, mapping them to the parametrized post-Einsteinian framework.

1101.2921
(/preprints)

2011-01-18, 12:29
**[edit]**

**Authors**: Ian Vega, Barry Wardell, Peter Diener

**Date**: 14 Jan 2011

**Abstract**: Numerical evaluation of the self-force on a point particle is made difficult by the use of delta functions as sources. Recent methods for self-force calculations avoid delta functions altogether, using instead a finite and extended "effective source" for a point particle. We provide a review of the general principles underlying this strategy, using the specific example of a scalar point charge moving in a black hole spacetime. We also report on two new developments: (i) the construction and evaluation of an effective source for a scalar charge moving along a generic orbit of an arbitrary spacetime, and (ii) the successful implementation of hyperboloidal slicing that significantly improves on previous treatments of boundary conditions used for effective-source-based self-force calculations. Finally, we identify some of the key issues related to the effective source approach that will need to be addressed by future work.

1101.2925
(/preprints)

2011-01-18, 12:29
**[edit]**

**Authors**: Sean T. McWilliams, Janna Levin

**Date**: 10 Jan 2011

**Abstract**: The coalescence of black hole-neutron star binaries is expected to be a principal source of gravitational waves for the next generation of detectors, Advanced LIGO and Advanced Virgo. Ideally, these and other gravitational wave sources would have a distinct electromagnetic counterpart, as significantly more information could be gained through two separate channels. In addition, since these detectors will probe distances with non-negligible redshift, a coincident observation of an electromagnetic counterpart to a gravitational wave signal would facilitate a novel measurement of dark energy [1]. For black hole masses not much larger than the neutron star mass, the tidal disruption and subsequent accretion of the neutron star by the black hole provides one avenue for generating an electromagnetic counterpart [2]. However, in this work, we demonstrate that, for all black hole-neutron star binaries observable by Advanced LIGO/Virgo, the interaction of the black hole with the magnetic field of the neutron star will drive a Poynting flux. This Poynting flux generates synchrotron/curvature radiation as the electron-positron plasma in the neutron star magnetosphere is accel- erated, and thermal radiation as the plasma is focused onto the neutron star magnetic poles, creating a "hot spot" on the neutron star surface. This novel effect will gener- ate copious luminosity, comparable to supernovae and active galactic nuclei, so that black hole-neutron star coalescences detectable with gravitational waves by Advanced LIGO/Virgo could also potentially be detectable electromagnetically.

1101.1969
(/preprints)

2011-01-15, 12:10
**[edit]**

**Authors**: Jose Luis Jaramillo (1 and 2), Carlos F. Sopuerta (3), Priscilla Canizares (3) ((1) AEI, (2) LUTH, (3) ICE, CSIC-IEEC)

**Date**: 12 Jan 2011

**Abstract**: The modeling of the gravitational-wave emission from extreme-mass-ratio inspirals is crucial for their detection and analysis with the future space-based observatory LISA. The inspiral can be described as the action of a local force, the self-force, determined by the gravitational perturbations created by the small object, described as a point mass, on the background geometry. The calculation of the self-force is a challenging task that requires the control of sources of error such as spurious modes or numerical noise. Here we address the question of the possible emergence of a persistent spurious solution in time-domain schemes, referred to as a Jost junk solution in the literature, that may contaminate self-force calculations. Previous studies suggested that Jost solutions are due to the use of zero initial data, which is inconsistent with the singular sources associated with the point mass. However, in this work we show that the specific origin is an inconsistency in the translation of the singular sources into jump conditions. More importantly, we identify the correct implementation of the sources at late times as the sufficient condition guaranteeing the absence of Jost junk solutions.

1101.2324
(/preprints)

2011-01-15, 12:09
**[edit]**

**Authors**: Priscilla Canizares, Carlos F. Sopuerta (ICE, CSIC-IEEC)

**Date**: 13 Jan 2011

**Abstract**: The computation of the self-force constitutes one of the main challenges for the construction of precise theoretical waveform templates in order to detect and analyze extreme-mass-ratio inspirals with the future space-based gravitational-wave observatory LISA. Since the number of templates required is quite high, it is important to develop fast algorithms both for the computation of the self-force and the production of waveforms. In this article we show how to tune a recent time-domain technique for the computation of the self-force, what we call the Particle without Particle scheme, in order to make it very precise and at the same time very efficient. We also extend this technique in order to allow for highly eccentric orbits.

1101.2526
(/preprints)

2011-01-15, 12:08
**[edit]**

**Authors**: Justin Vines, Tanja Hinderer, Éanna É. Flanagan

**Date**: 9 Jan 2011

**Abstract**: The gravitational wave signal from an inspiralling binary neutron star system will contain detailed information about tidal coupling in the system, and thus, about the internal physics of the neutron stars. To extract this information will require highly accurate models for the gravitational waveform. We present here a calculation of the gravitational wave signal from a binary with quadrupolar tidal interactions which includes all post-1-Newtonian-order effects in both the conservative dynamics and wave generation. We consider stars with adiabatically induced quadrupoles moving in circular orbits, and work to linear in the stars' quadrupole moments. We find that post-1-Newtonian corrections increase the tidal signal by approximately 20% at gravitational wave frequencies of 400 Hz.

1101.1673
(/preprints)

2011-01-11, 13:40
**[edit]**

**Authors**: Ian Harry, Stephen Fairhurst

**Date**: 7 Jan 2011

**Abstract**: In this paper we present a method for conducting a coherent search for single spin compact binary coalescences in gravitational wave data and compare this search to the existing coincidence method for single spin searches. We propose a method to characterize the regions of the parameter space where the single spin search, both coincident and coherent, will increase detection efficiency over the existing non-precessing search. We also show example results of the coherent search on a stretch of data from LIGO's fourth science run but note that a set of signal based vetoes will be needed before this search can be run to try to make detections.

1101.1459
(/preprints)

2011-01-09, 23:00
**[edit]**

**Authors**: Walter Del Pozzo, John Veitch, Alberto Vecchio

**Date**: 7 Jan 2011

**Abstract**: Second generation interferometric gravitational wave detectors, such as Advanced LIGO and Advanced Virgo, are expected to begin operation by 2015. Such instruments plan to reach sensitivities that will offer the unique possibility to test General Relativity in the dynamical, strong field regime and investigate departures from its predictions, in particular using the signal from coalescing binary systems. We introduce a statistical framework based on Bayesian model selection in which the Bayes factor between two competing hypotheses measures which theory is favored by the data. Probability density functions of the model parameters are then used to quantify the inference on individual parameters. We also develop a method to combine the information coming from multiple independent observations of gravitational waves, and show how much stronger inference could be. As an introduction and illustration of this framework - and a practical numerical implementation through the Monte Carlo integration technique of nested sampling - we apply it to gravitational waves from the inspiral phase of coalescing binary systems as predicted by General Relativity and a very simple alternative theory in which the graviton has a non-zero mass. This method can trivially (and should) be extended to more realistic and physically motivated theories.

1101.1391
(/preprints)

2011-01-09, 23:00
**[edit]**

**Authors**: Jonathan R. Gair, Eanna E. Flanagan, Steve Drasco, Tanja Hinderer, Stanislav Babak

**Date**: 22 Dec 2010

**Abstract**: We present two methods for integrating forced geodesic equations in the Kerr spacetime, which can accommodate arbitrary forces. As a test case, we compute inspirals under a simple drag force, mimicking the presence of gas. We verify that both methods give the same results for this simple force. We find that drag generally causes eccentricity to increase throughout the inspiral. This is a relativistic effect qualitatively opposite to what is seen in gravitational-radiation-driven inspirals, and similar to what is observed in hydrodynamic simulations of gaseous binaries. We provide an analytic explanation by deriving the leading order relativistic correction to the Newtonian dynamics. If observed, an increasing eccentricity would provide clear evidence that the inspiral was occurring in a non-vacuum environment. Our two methods are especially useful for evolving orbits in the adiabatic regime. Both use the method of osculating orbits, in which each point on the orbit is characterized by the parameters of the geodesic with the same instantaneous position and velocity. Both methods describe the orbit in terms of the geodesic energy, axial angular momentum, Carter constant, azimuthal phase, and two angular variables that increase monotonically and are relativistic generalizations of the eccentric anomaly. The two methods differ in their treatment of the orbital phases and the representation of the force. In one method the geodesic phase and phase constant are evolved together as a single orbital phase parameter, and the force is expressed in terms of its components on the Kinnersley orthonormal tetrad. In the second method, the phase constants of the geodesic motion are evolved separately and the force is expressed in terms of its Boyer-Lindquist components. This second approach is a generalization of earlier work by Pound and Poisson for planar forces in a Schwarzschild background.

1012.5111
(/preprints)

2011-01-07, 22:18
**[edit]**

**Authors**: Kipp Cannon, Chad Hanna, Drew Keppel, Antony C. Searle

**Date**: 3 Jan 2011

**Abstract**: The detection of gravitational waves from compact binaries relies on a computationally burdensome processing of gravitational-wave detector data. The parameter space of compact-binary-coalescence gravitational waves is large and optimal detection strategies often require nearly redundant calculations. Previously, it has been shown that singular value decomposition of search filters removes redundancy. Here we will demonstrate the use of singular value decomposition for a composite detection statistic. This can greatly improve the prospects for a computationally feasible rapid detection scheme across a large compact binary parameter space.

1101.0584
(/preprints)

2011-01-07, 22:18
**[edit]**

**Authors**: Alexander E. Rodin

**Date**: 30 Dec 2010

**Abstract**: We suggest a new approach to the detection of gravitational waves using observations of a group of millisecond pulsars. In contrast to the usual method, based on increasing the accuracy of the arrival times of pulses by excluding possible distorting factors, our method supposes that the additive phase noise that is inevitably present even in the most accurate observational data has various spectral components, which have characteristic amplitudes and begin to appear on different time scales. We use the "Caterpillar" (Singular Spectral Analysis, SSA) method to decompose the signal into its components. Our initial data are the residuals of the pulse arrival times for six millisecond pulsars. We constructed the angular correlation function for components of the decomposition of a given number, whose theoretical form for the case of an isotropic and homogeneous gravitational-wave background is known. The individual decomposition components show a statistically significant agreement with the theoretical expectations (correlation coefficient $\rho=0.92\pm 0.10$).

1101.0063
(/preprints)

2011-01-07, 22:18
**[edit]**

**Authors**: Elise Jennings, Carlton M. Baugh, Silvia Pascoli

**Date**: 12 Nov 2010

**Abstract**: Future galaxy surveys hope to distinguish between the dark energy and modified gravity scenarios for the accelerating expansion of the Universe using the distortion of clustering in redshift space. The aim is to model the form and size of the distortion to infer the rate at which large scale structure grows. We test this hypothesis and assess the performance of current theoretical models for the redshift space distortion using large volume N-body simulations of the gravitational instability process. We simulate competing cosmological models which have identical expansion histories - one is a quintessence dark energy model with a scalar field and the other is a modified gravity model with a time varying gravitational constant - and demonstrate that they do indeed produce different redshift space distortions. This is the first time this approach has been verified using a technique that can follow the growth of structure at the required level of accuracy. Our comparisons show that theoretical models for the redshift space distortion based on linear perturbation theory give a surprisingly poor description of the simulation results. Furthermore, the application of such models can give rise to catastrophic systematic errors leading to incorrect interpretation of the observations. We show that an improved model is able to extract the correct growth rate. Further enhancements to theoretical models of redshift space distortions, calibrated against simulations, are needed to fully exploit the forthcoming high precision clustering measurements.

1011.2842
(/preprints)

2011-01-07, 22:18
**[edit]**

**Authors**: P. G. Komorowski, S. R. Valluri, M. Houde

**Date**: 5 Jan 2011

**Abstract**: In an extreme mass ratio binary black hole system, a non-equatorial orbit will list (i.e. increase its angle of inclination, ${\iota}$) as it evolves in Kerr spacetime. The abutment, a set of evolving near-polar retrograde orbits for which the instantaneous Carter constant (${Q)}$ is at its maximum value (${Q}_{X}$), for given values of latus rectum (${\tilde{l}}$) and eccentricity (${e}$), has been introduced as a device by which the consistency of $dQ/dt$ with corresponding evolution equations for $d\tilde{l}% /dt$ and $de/dt$ might be tested, and as a means of elucidating second-order effects on the listing rate of the orbital angle of inclination, $\partial {% \iota}/\partial {t}$ (independently of a specific radiation back-reaction model). Our present work expands upon these two uses.

1101.0996
(/preprints)

2011-01-07, 22:18
**[edit]**

**Authors**: L. G. Althaus, A. H. Corsico, S. Torres, P. Loren-Aguilar, J. Isern, E. Garcia-Berro

**Date**: 5 Jan 2011

**Abstract**: Within the theoretical framework of some modern unification theories the constants of nature are functions of cosmological time. White dwarfs offer the possibility of testing a possible variation of G and, thus, to place constraints to these theories. We present full white dwarf evolutionary calculations in the case that G decreases with time. White dwarf evolution is computed in a self-consistent way, including the most up-to-date physical inputs, non-gray model atmospheres and a detailed core chemical composition that results from the calculation of the full evolution of progenitor stars. We find that the mechanical structure and the energy balance of white dwarfs are strongly modified by the presence of a varying G. In particular, for certain values of the rate of change of G, the evolution of cool white dwarfs is markedly affected. The impact of a varying G is more notorious in the case of more massive white dwarfs. In view of the recent results reporting that a very accurate white dwarf cooling age can be derived for the old and metal-rich open cluster NGC 6791, our study suggests that this cluster could be a potential target to constrain or detect a ypothetical secular variation of G.

1101.0986
(/preprints)

2011-01-07, 22:18
**[edit]**

**Authors**: F Antonucci, M Armano, H Audley, G Auger, M Benedetti, P Binetruy, C Boatella, J Bogenstahl, D Bortoluzzi, P Bosetti, N Brandt, M Caleno, A Cavalleri, M Cesa, M Chmeissani, G Ciani, A Conchillo, G Congedo, I Cristofolini, M Cruise, K Danzmann, F De Marchi, M Diaz-Aguilo, I Diepholz, G Dixon, R Dolesi, N Dunbar, J Fauste, L Ferraioli, D Fertin, W Fichter, E Fitzsimons, M Freschi, A García Marin, C García Marirrodriga, R Gerndt, L Gesa, D Giardini, F Gibert, C Grimani, A Grynagier, B Guillaume, F Guzmán, I Harrison, G Heinzel, M Hewitson, D Hollington, J Hough, D Hoyland, M Hueller, J Huesler, O Jeannin, O Jennrich, P Jetzer, B Johlander, C Killow, X Llamas, I Lloro, A Lobo, R Maarschalkerweerd, S Madden, D Mance, I Mateos, P W McNamara, J Mendestì, E Mitchell, A Monsky, D Nicolini, D Nicolodi, M Nofrarias, F Pedersen, M Perreur-Lloyd, A Perreca, E Plagnol, P Prat, G D Racca, B Rais, J Ramos-Castro, J Reiche, J A Romera Perez, D Robertson, H Rozemeijer, J Sanjuan, A Schleicher, M Schulte, D Shaul, L Stagnaro, S Strandmoe, F Steier, T J Sumner, A Taylor, D Texier, C Trenkel, D Tombolato, S Vitale, G Wanner, H Ward, S Waschke, P Wass, W J Weber, P Zweifel

**Date**: 29 Dec 2010

**Abstract**: This paper presents a quantitative assessment of the performance of the upcoming LISA Pathfinder geodesic explorer mission. The findings are based on the results of extensive ground testing and simulation campaigns using flight hardware and flight control and operations algorithms. The results show that, for the central experiment of measuring the stray differential acceleration between the LISA test masses, LISA Pathfinder will be able to verify the overall acceleration noise to within a factor two of the LISA requirement at 1 mHz and within a factor 10 at 0.1 mHz. We also discuss the key elements of the physical model of disturbances, coming from LISA Pathfinder and ground measurement, that will guarantee the LISA performance.

1012.5968
(/preprints)

2011-01-04, 13:34
**[edit]**

**Authors**: Sarp Akcay

**Date**: 29 Dec 2010

**Abstract**: Fast, reliable orbital evolutions of compact objects around massive black holes will be needed as input for gravitational wave search algorithms in the data stream generated by the planned Laser Interferometer Space Antenna (LISA). Currently, the state of the art is a time-domain code by [Phys. Rev. D{\bf 81}, 084021, (2010)] that computes the gravitational self-force on a point-particle in an eccentric orbit around a Schwarzschild black hole. Currently, time-domain codes take up to a few days to compute just one point in parameter space. In a series of articles, we advocate the use of a frequency-domain approach to the problem of gravitational self-force (GSF) with the ultimate goal of orbital evolution in mind. Here, we compute the GSF for a particle in a circular orbit in Schwarzschild spacetime. We solve the linearized Einstein equations for the metric perturbation in Lorenz gauge. Our frequency-domain code reproduces the time-domain results for the GSF up to $\sim 1000$ times faster for small orbital radii. In forthcoming companion papers, we will generalize our frequency-domain methods to include bound (eccentric) orbits in Schwarzschild and (eventually) Kerr spacetimes for computing the GSF, where we will employ the method of extended homogeneous solutions [Phys. Rev. D {\bf 78}, 084021 (2008)].

1012.5860
(/preprints)

2011-01-04, 13:32
**[edit]**

© M. Vallisneri 2012 — last modified on 2010/01/29

*Tantum in modicis, quantum in maximis*