[1012.5172] Phenomenological gravitational waveforms from spinning coalescing binaries

Authors: R. Sturani, S. Fischetti, L. Cadonati, G. M. Guidi, J. Healy, D. Shoemaker, A. Vicere'

Date: 23 Dec 2010

Abstract: An accurate knowledge of the coalescing binary gravitational waveform is crucial for match filtering techniques, which are currently used in the observational searches performed by the LIGO-Virgo collaboration. Following an earlier paper by the same authors we expose the construction of analytical phenomenological waveforms describing the signal sourced by generically spinning binary systems. The gap between the initial inspiral part of the waveform, described by spin-Taylor approximants, and its final ring-down part, described by damped exponentials, is bridged by a phenomenological phase calibrated by comparison with the dominant spherical harmonic mode of a set of waveforms including both numerical and phenomenological waveforms of a different type. All waveforms considered describe equal mass systems with dimension-less spin magnitudes equal to 0.6. The noise-weighted overlap integral between numerical and phenomenological waveforms ranges between 0.93 and 0.98 for a wide span of mass values.

abs pdf

Dec 24, 2010

1012.5172 (/preprints)
2010-12-24, 14:23 [edit]

[1012.4939] A targeted coherent search for gravitational waves from compact binary coalescences

Authors: Ian Harry, Stephen Fairhurst

Date: 22 Dec 2010

Abstract: We present the details of a method for conducting a targeted, coherent search for compact binary coalescences. The search is tailored to be used as a followup to electromagnetic transients such as Gamma Ray Bursts. We derive the coherent search statistic for Gaussian detector noise and discuss the benefits of a coherent, multi-detector search over coincidence methods. To mitigate the effects of non-stationary data, we introduce a number of signal consistency tests, including the null SNR, amplitude consistency and several $\chiˆ{2}$ tests. We demonstrate the search performance on Gaussian noise and on data from LIGO's fourth science run and verify that the signal consistency tests are capable of removing the majority of noise transients and the search gives an efficiency comparable to that achieved in Gaussian noise.

abs pdf

Dec 23, 2010

1012.4939 (/preprints)
2010-12-23, 16:43 [edit]

[1012.4423] Characterization of the gravitational wave emission of three black holes

Authors: Pablo Galaviz, Bernd Bruegmann

Date: 20 Dec 2010

Abstract: We study the gravitational wave emission of three compact objects using post-Newtonian (PN) equations of motion derived from the ADM-Hamiltonian formulation, where we include (for the first time in this context) terms up to 2.5 PN order. We perform numerical simulations of a hierarchical configuration of three compact bodies in which a binary system is perturbed by a third, lighter body. The relative importance of the different PN orders is examined. We compute the waveform in the linear regime considering mass quadrupole, current quadrupole and mass octupole contributions. Performing a spherical harmonic decomposition of the waveforms we find that from the $l=3$ modes it is possible to extract information about the third body, in particular the period, eccentricity of its orbit, and the inclination angle between the inner and outer binary orbits.

abs pdf

Dec 22, 2010

1012.4423 (/preprints)
2010-12-22, 12:32 [edit]

[1012.4530] Multi-baseline gravitational wave radiometry

Authors: Dipongkar Talukder, Sanjit Mitra, Sukanta Bose

Date: 21 Dec 2010

Abstract: We present a statistic for the detection of stochastic gravitational-wave backgrounds (SGWBs) using radiometry with a network of multiple baselines. We also quantitatively compare the sensitivities of existing baselines, and their network, to SGWBs. We assess how the measurement accuracy of signal parameters, e.g., the sky position of a localized source, can improve when using a network of baselines as compared to any of the single participating baselines. The search statistic itself is derived from the likelihood ratio of the cross-correlation of the data across all possible baselines in a detector network, and is optimal in Gaussian noise. Specifically, it is the likelihood-ratio maximized over the strength of the SGWB, and is called the maximized likelihood ratio (MLR). One of the main advantages of using the MLR over past search strategies for inferring the presence or absence of a signal is that the former does not require the deconvolution of the cross-correlation statistic. Therefore, it does not suffer from errors inherent to the deconvolution procedure and is, especially, useful for detecting weak sources. In the limit of a single baseline, it reduces to the detection statistic studied by Ballmer [Class. Quant. Grav. 23, S179 (2006)] and Mitra et al. [Phys. Rev. D 77, 042002 (2008)]. Unlike past studies, here the MLR statistic enables us to compare quantitatively the performances of a variety of baselines searching for a SGWB signal in (simulated) data. Although we use simulated noise and SGWB signals for making these comparisons, our method can be straightforwardly applied on real data.

abs pdf

Dec 22, 2010

1012.4530 (/preprints)
2010-12-22, 12:30 [edit]

[1012.4695] Blind surveys for radio pulsars and transients

Authors: D.R. Lorimer

Date: 21 Dec 2010

Abstract: The main reasons for searching for pulsars are to: (i) get an accurate census of the neutron star population and its origin and evolution; (ii) connect neutron stars to other stellar populations in the Galaxy and globular clusters; (iii) study Galactic astronomy (the interstellar medium and magnetic field); (iv) find and study new interesting individual objects; (v) study pulsar phenomenology; (vi) find pulsars to add to the sensitivity of pulsar timing arrays. This review focuses on blind (i.e. large area) searches for radio pulsars. I'll summarize the methods we use, some of the challenges they present, look at some of the recent and current efforts going on. I will also look at outreach of this area to groups outside the traditional area of pulsar research, highlight the discoveries of radio transients and look ahead to the future. Pulsars found at other wavelengths will be reviewed elsewhere in this volume.

abs pdf

Dec 22, 2010

1012.4695 (/preprints)
2010-12-22, 12:29 [edit]

[1012.4466] Tidal stellar disruptions by massive black hole pairs: II. Decaying binaries

Authors: Xian Chen, Alberto Sesana, Piero Madau, Fukun K. Liu

Date: 20 Dec 2010

Abstract: Tidal stellar disruptions have traditionally been discussed as a probe of the single, massive black holes (MBHs) that are dormant in the nuclei of galaxies. In Chen et al. (2009), we used numerical scattering experiments to show that three-body interactions between bound stars in a stellar cusp and a non-evolving "hard" MBH binary will also produce a burst of tidal disruptions, caused by a combination of the secular "Kozai effect" and by close resonant encounters with the secondary hole. Here we derive basic analytical scalings of the stellar disruption rates with the system parameters, assess the relative importance of the Kozai and resonant encounter mechanisms as a function of time, discuss the impact of general relativistic (GR) and extended stellar cusp effects, and develop a hybrid model to self-consistently follow the shrinking of an MBH binary in a stellar background, including slingshot ejections and tidal disruptions. In the case of a fiducial binary with primary hole mass M_1=10ˆ7\msun and mass ratio q=M_2/M_1=1/81, embedded in an isothermal cusp, we derive a stellar disruption rate \dot{N_*} ~ 0.2\,yrˆ{-1} lasting ~ 3X10ˆ5 yr. This rate is 3 orders of magnitude larger than the corresponding value for a single MBH fed by two-body relaxation, confirming our previous findings. For q<<0.01, the Kozai/chaotic effect could be quenched due to GR/cusp effects by an order of magnitude, but even in this case the stellar-disruption rate is still two orders of magnitude larger than that given by standard relaxation processes around a single MBH. Our results suggest that >10% of the tidal-disruption events may originate in MBH binaries.

abs pdf

Dec 22, 2010

1012.4466 (/preprints)
2010-12-22, 12:28 [edit]

[1012.4043] Stereoscopic visualization in curved spacetime: seeing deep inside a black hole

Authors: Andrew J. S. Hamilton, Gavin Polhemus

Date: 18 Dec 2010

Abstract: Stereoscopic visualization adds an additional dimension to the viewer's experience, giving them a sense of distance. In a general relativistic visualization, distance can be measured in a variety of ways. We argue that the affine distance, which matches the usual notion of distance in flat spacetime, is a natural distance to use in curved spacetime. As an example, we apply affine distance to the visualization of the interior of a black hole. Affine distance is not the distance perceived with normal binocular vision in curved spacetime. However, the failure of binocular vision is simply a limitation of animals who have evolved in flat spacetime, not a fundamental obstacle to depth perception in curved spacetime. Trinocular vision would provide superior depth perception.

abs pdf

Dec 22, 2010

1012.4043 (/preprints)
2010-12-22, 08:27 [edit]

[1012.3894] Full-analytic frequency-domain gravitational wave forms from eccentric compact binaries to 2PN accuracy

Authors: Manuel Tessmer, Gerhard Schaefer

Date: 17 Dec 2010

Abstract: The article provides full-analytical gravitational wave (GW) forms for eccentric nonspinning compact binaries of arbitrary mass ratio in the time Fourier domain. We avoid, for the first time, the semi-analytical property of recent descriptions, i.e. the demand of inverting the higher-order Kepler equation numerically but keeping all other computations analytic.
The article is a completion of a previous article {(Tessmer and Sch\"afer, 2010. arXiv:1006.3714)} to second post-Newtonian (2PN) order in the harmonic GW amplitude and conservative orbital dynamics. The GW amplitudes are given in spherical tensor components. % A fully analytical inversion formula of the Kepler equation in harmonic coordinates is provided, as well as the analytic time Fourier expansion of trigonometric functions of the eccentric anomaly in terms of sines and cosines of the mean anomaly.

abs pdf

Dec 20, 2010

1012.3894 (/preprints)
2010-12-20, 09:24 [edit]

[1012.2879] Tracking the precession of compact binaries from their gravitational-wave signal

Authors: Patricia Schmidt, Mark Hannam, Sascha Husa, P. Ajith

Date: 13 Dec 2010

Abstract: We present a simple method to track the precession of a black-hole-binary system, using only information from the gravitational-wave (GW) signal. Our method consists of locating the frame from which the magnitude of the $(\ell=2,|m|=2)$ modes is maximized, which we denote the "quadrupole-aligned" frame. We demonstrate the efficacy of this method when applied to waveforms from numerical simulations. In the test case of an equal-mass nonspinning binary, our method locates the direction of the orbital angular momentum to within $(\Delta \theta, \Delta \phi) = (0.05ˆ{\circ},0.2ˆ{\circ})$. We then apply the method to a $q = M_2/M_1 = 3$ binary that exhibits significant precession. In general a spinning binary's orbital angular momentum $\mathbf{L}$ is \emph{not} orthogonal to the orbital plane. Evidence that our method locates the direction of $\mathbf{L}$ rather than the normal of the orbital plane is provided by comparison with post-Newtonian (PN) results. Also, we observe that it accurately reproduces similar higher-mode amplitudes to a comparable non-spinning (and therefore non-precessing) binary, and that the frequency of the $(\ell=2,|m|=2)$ modes is consistent with the "total frequency" of the binary's motion. The simple form of the quadrupole-aligned waveform will be useful in attempts to analytically model the inspiral-merger-ringdown (IMR) signal of precessing binaries, and in standardizing the representation of waveforms for studies of accuracy and consistency of source modelling efforts, both numerical and analytical.

abs pdf

Dec 15, 2010

1012.2879 (/preprints)
2010-12-15, 14:27 [edit]

[1012.3144] Effective Gravitational Wave Stress-energy Tensor in Alternative Theories of Gravity

Authors: Leo C. Stein, Nicolas Yunes, Scott A. Hughes

Date: 14 Dec 2010

Abstract: The inspiral of binary systems in vacuum is controlled by the rate of change of the system's energy, angular momentum and Carter constant. In alternative theories, such a change is induced by the effective stress-energy carried away by gravitational radiation and any other propagating degrees of freedom. We employ perturbation theory and the short-wavelength approximation to compute this stress-energy tensor in a wide class of alternative theories. We find that this tensor is generally a modification of that first computed by Isaacson, where the corrections can dominate over the general relativistic term. In a wide class of theories, however, these corrections identically vanish at asymptotically flat, future, null infinity, reducing the stress-energy tensor to Isaacson's. We exemplify this phenomenon by first considering dynamical Chern-Simons modified gravity, which corrects the action via a scalar field and the contraction of the Riemann tensor and its dual. We then consider a wide class of theories with dynamical scalar fields coupled to higher-order curvature invariants, and show that the gravitational wave stress-energy tensor still reduces to Isaacson's. The calculations presented in this paper are crucial to perform systematic tests of such modified gravity theories through the orbital decay of binary pulsars or through gravitational wave observations.

abs pdf

Dec 15, 2010

1012.3144 (/preprints)
2010-12-15, 14:27 [edit]

[1012.2150] Long gravitational-wave transients and associated detection strategies for a network of terrestrial interferometers

Authors: Eric Thrane, Shivaraj Kandhasamy, Christian D Ott, Warren G Anderson, Nelson L Christensen, Michael W Coughlin, Steven Dorsher, Stefanos Giampanis, Vuk Mandic, Antonis Mytidis, Tanner Prestegard, Peter Raffai, Bernard Whiting

Date: 10 Dec 2010

Abstract: Searches for gravitational waves (GWs) traditionally focus on persistent sources (e.g., pulsars or the stochastic background) or on transients sources (e.g., compact binary inspirals or core-collapse supernovae), which last for timescales of milliseconds to seconds. We explore the possibility of long GW transients with unknown waveforms lasting from many seconds to weeks. We propose a novel analysis technique to bridge the gap between short O(s) burst analyses and persistent stochastic analyses. Our technique utilizes frequency-time maps of GW strain cross-power between two spatially separated terrestrial GW detectors. The application of our cross-power statistic to searches for GW transients is framed as a pattern recognition problem, and we discuss several pattern-recognition techniques. We demonstrate these techniques by recovering simulated GW signals in simulated detector noise. We also recover environmental noise artifacts, thereby demonstrating a novel technique for the identification of such artifacts in GW interferometers. We compare the efficiency of this framework to other techniques such as matched filtering.

abs pdf

Dec 15, 2010

1012.2150 (/preprints)
2010-12-15, 14:27 [edit]

[1012.2456] Binary black hole coalescence in the extreme-mass-ratio limit: testing and improving the effective-one-body multipolar waveform

Authors: Sebastiano Bernuzzi, Alessandro Nagar, Anil Zenginoglu

Date: 11 Dec 2010

Abstract: We discuss the properties of the effective-one-body (EOB) multipolar gravitational waveform emitted by nonspinning black-hole binaries of masses $\mu$ and $M$ in the extreme-mass-ratio limit, $\mu/M=\nu\ll 1$. We focus on the transition from quasicircular inspiral to plunge, merger and ringdown.We compare the EOB waveform to a Regge-Wheeler-Zerilli (RWZ) waveform computed using the hyperboloidal layer method and extracted at null infinity. Because the EOB waveform keeps track analytically of most phase differences in the early inspiral, we do not allow for any arbitrary time or phase shift between the waveforms. The dynamics of the particle, common to both wave-generation formalisms, is driven by leading-order ${\cal O}(\nu)$ analytically--resummed radiation reaction. The EOB and the RWZ waveforms have an initial dephasing of about $5\times 10ˆ{-4}$ rad and maintain then a remarkably accurate phase coherence during the long inspiral ($\sim 33$ orbits), accumulating only about $-2\times 10ˆ{-3}$ rad until the last stable orbit, i.e. $\Delta\phi/\phi\sim -5.95\times 10ˆ{-6}$. We obtain such accuracy without calibrating the analytically-resummed EOB waveform to numerical data, which indicates the aptitude of the EOB waveform for LISA-oriented studies. We then improve the behavior of the EOB waveform around merger by introducing and tuning next-to-quasi-circular corrections both in the gravitational wave amplitude and phase. For each multipole we tune only four next-to-quasi-circular parameters by requiring compatibility between EOB and RWZ waveforms at the light-ring. The resulting phase difference around merger time is as small as $\pm 0.015$ rad, with a fractional amplitude agreement of $2.5%$. This suggest that next-to-quasi-circular corrections to the phase can be a useful ingredient in comparisons between EOB and numerical relativity waveforms.

abs pdf

Dec 14, 2010

1012.2456 (/preprints)
2010-12-14, 14:04 [edit]

[1012.1853] Dynamics and Gravitational Wave Signature of Collapsar Formation

Authors: C. D. Ott (1), C. Reisswig (1), E. Schnetter (2), E. O&#x27;Connor (1), U. Sperhake (3), F. Loeffler (2), P. Diener (2), E. Abdikamalov (2), I. Hawke (4), A. Burrows (5) ((1) Caltech, (2) LSU, (3) CSIC-IEEC Barcelona, (4) Southampton, (5) Princeton)

Date: 8 Dec 2010

Abstract: We perform 3+1 general relativistic simulations of rotating core collapse in the context of the collapsar model for long gamma-ray bursts. We employ a realistic progenitor, rotation based on results of stellar evolution calculations, and a simplified equation of state. Our simulations track self-consistently collapse, bounce, the postbounce phase, black hole formation, and the subsequent early hyperaccretion phase. We extract gravitational waves from the spacetime curvature and identify a unique gravitational wave signature associated with the early phase of collapsar formation.

abs pdf

Dec 10, 2010

1012.1853 (/preprints)
2010-12-10, 11:45 [edit]

[1012.1602] Sgr A*: The Optimal Testbed of Strong-Field Gravity

Authors: Dimitrios Psaltis, Tim Johannsen (Arizona)

Date: 7 Dec 2010

Abstract: The black hole in the center of the Milky Way has been observed and modeled intensely during the last decades. It is also the prime target of a number of new experiments that aim to zoom into the vicinity of its horizon and reveal the inner working of its spacetime. In this review we discuss our current understanding of the gravitational field of Sgr A* and the prospects of testing the Kerr nature of its spacetime via imaging, astrometric, and timing observations.

abs pdf

Dec 09, 2010

1012.1602 (/preprints)
2010-12-09, 10:43 [edit]

[1012.1656] Are There Echoes From The Pre-Big Bang Universe? A Search for Low Variance Circles in the CMB Sky

Authors: Amir Hajian

Date: 8 Dec 2010

Abstract: The existence of concentric low variance circles in the CMB sky, generated by black-hole encounters in an aeon preceding our big bang, is a prediction of the Conformal Cyclic Cosmology. Detection of three families of such circles in WMAP data was recently reported by Gurzadyan & Penrose (2010). We reassess the statistical significance of those circles by comparing with Monte Carlo simulations of the CMB sky with realistic modeling of the anisotropic noise in WMAP data. We find that the circles are not anomalous and that all three groups are consistent at 3sigma level with a Gaussian CMB sky as predicted by inflationary cosmology model.

abs pdf

Dec 09, 2010

1012.1656 (/preprints)
2010-12-09, 10:42 [edit]

[1012.1549] Reducing orbital eccentricity in quasi-circular binary black-hole evolutions in presence of spins

Authors: Alessandra Buonanno, Lawrence E. Kidder, Abdul H. Mrou&#xe9;, Harald P. Pfeiffer, Andrea Taracchini

Date: 7 Dec 2010

Abstract: Building initial conditions for generic binary black-hole evolutions without initial spurious eccentricity remains a challenge for numerical-relativity simulations. This problem can be overcome by applying an eccentricity-removal procedure which consists in evolving the binary for a couple of orbits, estimating the eccentricity, and then correcting the initial conditions. The presence of spins can complicate this procedure. As predicted by post-Newtonian theory, spin-spin interactions and precession prevent the binary from moving along an adiabatic sequence of spherical orbits, inducing oscillations in the radial separation and in the orbital frequency. However, spin-induced oscillations occur at approximately twice the orbital frequency, therefore they can be distinguished from the initial spurious eccentricity, which occurs at approximately the orbital frequency. We develop a new removal procedure based on the derivative of the orbital frequency and find that it is successful in reducing the eccentricity measured in the orbital frequency to less than 0.0001 when moderate spins are present. We test this new procedure using numerical-relativity simulations of binary black holes with mass ratios 1.5 and 3, spin magnitude 0.5 and various spin orientations. The numerical simulations exhibit spin-induced oscillations in the dynamics at approximately twice the orbital frequency. Oscillations of similar frequency are also visible in the gravitational-wave phase and frequency of the dominant mode.

abs pdf

Dec 08, 2010

1012.1549 (/preprints)
2010-12-08, 08:59 [edit]

[1012.1194] Does an atom interferometer test the gravitational redshift at the Compton frequency ?

Authors: Peter Wolf, Luc Blanchet, Christian J. Bord&#xe9;, Claude Cohen-Tannoudji, Christophe Salomon, Serge Reynaud

Date: 6 Dec 2010

Abstract: Atom interferometers allow the measurement of the acceleration of freely falling atoms with respect to an experimental platform at rest on Earth's surface. Such experiments have been used to test the universality of free fall by comparing the acceleration of the atoms to that of a classical freely falling object. In a recent paper, M\"uller, Peters and Chu [Nature {\bf 463}, 926-929 (2010)] argued that atom interferometers also provide a very accurate test of the gravitational redshift when considering the atom as a clock operating at the Compton frequency associated with the rest mass. We analyze this claim in the frame of general relativity and of different alternative theories. We show that the difference of "Compton phases" between the two paths of the interferometer is actually zero in a large class of theories, including general relativity, all metric theories of gravity, most non-metric theories and most theoretical frameworks used to interpret the violations of the equivalence principle. Therefore, in most plausible theoretical frameworks, there is no redshift effect and atom interferometers only test the universality of free fall. We also show that frameworks in which atom interferometers would test the redshift pose dreadful problems, such as (i) violation of the Schiff conjecture, (ii) violation of the Feynman path integral formulation of quantum mechanics and of the principle of least action for matter waves, (iii) violation of energy conservation, and more generally (iv) violation of the particle-wave duality in quantum mechanics. Standard quantum mechanics is no longer valid in such frameworks, so that a consistent interpretation of the experiment would require an alternative formulation of quantum mechanics. As such an alternative has not been proposed to date, we conclude that the interpretation of atom interferometers as testing the gravitational redshift is unsound.

abs pdf

Dec 06, 2010

1012.1194 (/preprints)
2010-12-06, 19:23 [edit]

[1012.0908] Sensitivity Studies for Third-Generation Gravitational Wave Observatories

Authors: S. Hild, M. Abernathy, F. Acernese, P. Amaro-Seoane, N. Andersson, K. Arun, F. Barone, B. Barr, M. Barsuglia, M. Beker, N. Beveridge, S. Birindelli, S. Bose, L. Bosi, S. Braccini, C. Bradaschia, T. Bulik, E. Calloni, G. Cella, E. Chassande Mottin, S. Chelkowski, A. Chincarini, J. Clark, E. Coccia, C. Colacino, J. Colas, A. Cumming, L. Cunningham, E. Cuoco, S. Danilishin, K. Danzmann, R. De Salvo, T. Dent, R. De Rosa, L. Di Fiore, A. Di Virgilio, M. Doets, V. Fafone, P. Falferi, R. Flaminio, J. Franc, F. Frasconi, A. Freise, D. Friedrich, P. Fulda, J. Gair, G. Gemme, E. Genin, A. Gennai, A. Giazotto, K. Glampedakis, C. Gr&#xe4;f, M. Granata, H. Grote, G. Guidi, A. Gurkovsky, G. Hammond, M. Hannam, J. Harms, D. Heinert, M. Hendry, I. Heng, E. Hennes, J. Hough, S. Husa, S. Huttner, G. Jones, F. Khalili, K. Kokeyama, K. Kokkotas, B. Krishnan, T.G.F. Li, M. Lorenzini, H. L&#xfc;ck, E. Majorana, I. Mandel, V. Mandic, M. Mantovani, I. Martin, C. Michel, Y. Minenkov, N. Morgado, S. Mosca, B Mours, H. M&#xfc;ller-Ebhardt, P. Murray, R. Nawrodt, J. Nelson, R. Oshaughnessy, C. D. Ott, C. Palomba, A. Paoli, G. Parguez, A. Pasqualetti, R. Passaquieti, D. Passuello, L. Pinard, W. Plastino, R. Poggiani1, P. Popolizio, M. Prato, M. Punturo, P. Puppo, D. Rabeling, P. Rapagnani, J. Read, T. Regimbau, H. Rehbein, S. Reid, F. Ricci, F. Richard, A. Rocchi, S. Rowan, A. R&#xfc;diger, L. Santamar&#xed;a, B. Sassolas, B. Sathyaprakash, R. Schnabel, C. Schwarz, P. Seidel, A. Sintes, K. Somiya, F. Speirits, K. Strain, S Strigin, P. Sutton, S. Tarabrin, A. Th&#xfc;ring, J. van den Brand, M. van Veggel, C. van den Broeck, A. Vecchio, J. Veitch, F. Vetrano, A. Vicere, S. Vyatchanin, B. Willke, G. Woan, K. Yamamoto

Date: 4 Dec 2010

Abstract: Advanced gravitational wave detectors, currently under construction, are expected to directly observe gravitational wave signals of astrophysical origin. The Einstein Telescope, a third-generation gravitational wave detector, has been proposed in order to fully open up the emerging field of gravitational wave astronomy. In this article we describe sensitivity models for the Einstein Telescope and investigate potential limits imposed by fundamental noise sources. A special focus is set on evaluating the frequency band below 10Hz where a complex mixture of seismic, gravity gradient, suspension thermal and radiation pressure noise dominates. We develop the most accurate sensitivity model, referred to as ET-D, for a third-generation detector so far, including the most relevant fundamental noise contributions.

abs pdf

Dec 06, 2010

1012.0908 (/preprints)
2010-12-06, 19:23 [edit]

[1012.0886] Hybrid black-hole binary initial data

Authors: Bruno C. Mundim, Bernard J. Kelly, Yosef Zlochower, Hiroyuki Nakano, Manuela Campanelli

Date: 4 Dec 2010

Abstract: Traditional black-hole binary puncture initial data is conformally flat. This unphysical assumption is coupled with a lack of radiation signature from the binary's past life. As a result, waveforms extracted from evolutions of this data display an abrupt jump. In Kelly et al. [Class.Quant.Grav.27:114005,2010], a new binary black-hole initial data with radiation contents derived in the post-Newtonian (PN) calculation was adapted to puncture evolutions in numerical relativity. This data satisfies the constraint equations to the 2.5PN order, and contains a transverse-traceless "wavy" metric contribution, violating the standard assumption of conformal flatness. Although the evolution contained less spurious radiation, there were undesired features; the unphysical horizon mass loss and the large initial orbital eccentricity. Introducing a hybrid approach to the initial data evaluation, we significantly reduce these undesired features.

abs pdf

Dec 06, 2010

1012.0886 (/preprints)
2010-12-06, 19:23 [edit]

[1011.4322] Accelerating Compact Object Mergers in Triple Systems with the Kozai Resonance: A Mechanism for "Prompt'' Type Ia Supernovae, Gamma-Ray Bursts, and Other Exotica

Authors: Todd A. Thompson

Date: 18 Nov 2010

Abstract: The mechanism of Type Ia supernovae and gamma-ray bursts (GRBs) is unknown, but a subset of both may be due to white dwarf-white dwarf (WD-WD) and neutron star-neutron star (NS-NS) mergers, respectively. A general problem with this picture is the production of binaries with semi-major axes small enough to merge via gravitational wave (GW) emission in significantly less than the Hubble time (t_H), and thus accommodate the observation that these events closely follow episodes of star formation in time. I explore the possibility that such systems are not binaries at all, but actually coeval, or dynamical formed, hierarchical triple systems. The tertiary induces Kozai oscillations in the inner binary, driving it to high eccentricity, and dramatically reducing its GW merger timescale. This effect significantly increases the allowed range of binary period P such that the merger time is t_merge < t_H. I find that Chandrasehkar mass binaries with P as large as ~300 days can in fact merge in < t_H if they contain a prograde solar-mass tertiary at high enough inclination. For systems with retrograde tertiaries, the allowed range of P such that t_merge < t_H is yet larger. In contrast, P < 0.3 days is required in the absence of a tertiary. I discuss implications of these findings for the production of Ia supernovae via WD-WD mergers, as well as GRBs formed via binary mergers composed of NSs, black holes, and WDs. Based on the statistics of solar-type binaries, I argue that nearly many tight WD-WD binaries should be in triple systems affected by the Kozai resonance. In analogy, the tightest NS-NS binaries may also have formed in triples. If true, expectations for the mHz GW signal from individual sources, the diffuse background, and the foreground for GW experiments like LISA are modified. This work motivates future studies of the triple fraction of intermediate mass A/B stars and massive O stars.

abs pdf

Dec 06, 2010

1011.4322 (/preprints)
2010-12-06, 15:52 [edit]

[1011.4518] Gravitational Pulse Astronomy

Authors: Andrew Gould (Ohio State)

Date: 19 Nov 2010

Abstract: Thompson has recently argued that the Kozai mechanism is primarily responsible for driving white-dwarf binary mergers and so generating type Ia supernovae (SNe). If this is the case, the gravitational wave signal from these systems will be characterized by isolated repeating pulses that are well approximated by parabolic encounters. I show that standard Fourier-based searches would do a very poor job of digging these sources out of the noise, and propose a new type matched filter search, which can improve sensitivity by up to a factor ~30 relative to Fourier. If these eccentric binaries account for even a modest fraction of the observed SN rate, then there should be of order 1 pulse every 20 seconds coming from within 1 kpc, and there should be of order a thousand detectable sources in this same volume. I outline methods of identifying these sources both to remove this very pernicious background to other signals, and to find candidate SN Ia progenitors, and I sketch practical methods to find optical counterparts to these sources and so measure their masses and distances.

abs pdf

Dec 06, 2010

1011.4518 (/preprints)
2010-12-06, 15:52 [edit]

[1012.0497] Feasibility and performances of compressed-sensing and sparse map-making with Herschel/PACS data

Authors: Nicolas Barbey, Marc Sauvage, Jean-Luc Starck, Roland Ottensamer, Pierre Chanial

Date: 2 Dec 2010

Abstract: The Herschel Space Observatory of ESA was launched in May 2009 and is in operation since. From its distant orbit around L2 it needs to transmit a huge quantity of information through a very limited bandwidth. This is especially true for the PACS imaging camera which needs to compress its data far more than what can be achieved with lossless compression. This is currently solved by including lossy averaging and rounding steps on board. Recently, a new theory called compressed-sensing emerged from the statistics community. This theory makes use of the sparsity of natural (or astrophysical) images to optimize the acquisition scheme of the data needed to estimate those images. Thus, it can lead to high compression factors.
A previous article by Bobin et al. (2008) showed how the new theory could be applied to simulated Herschel/PACS data to solve the compression requirement of the instrument. In this article, we show that compressed-sensing theory can indeed be successfully applied to actual Herschel/PACS data and give significant improvements over the standard pipeline. In order to fully use the redundancy present in the data, we perform full sky map estimation and decompression at the same time, which cannot be done in most other compression methods. We also demonstrate that the various artifacts affecting the data (pink noise, glitches, whose behavior is a priori not well compatible with compressed-sensing) can be handled as well in this new framework. Finally, we make a comparison between the methods from the compressed-sensing scheme and data acquired with the standard compression scheme. We discuss improvements that can be made on ground for the creation of sky maps from the data.

abs pdf

Dec 02, 2010

1012.0497 (/preprints)
2010-12-02, 21:14 [edit]

[1010.1302] LISA Sensitivities to Gravitational Waves from Relativistic Metric Theories of Gravity

Authors: Massimo Tinto, M&#xe1;rcio Eduardo da Silva Alves

Date: 6 Oct 2010

Abstract: The direct observation of gravitational waves will provide a unique tool for probing the dynamical properties of highly compact astrophysical objects, mapping ultra-relativistic regions of space-time, and testing Einstein's general theory of relativity. LISA (Laser Interferometer Space Antenna), a joint NASA-ESA mission to be launched in the next decade, will perform these scientific tasks by detecting and studying low-frequency cosmic gravitational waves through their influence on the phases of six modulated laser beams exchanged between three remote spacecraft. By directly measuring the polarization components of the waves LISA will detect, we will be able to test Einstein's theory of relativity with good sensitivity. Since a gravitational wave signal predicted by the most general relativistic metric theory of gravity accounts for {\it six} polarization modes (the usual two Einstein's tensor polarizations as well as two vector and two scalar wave components), we have derived the LISA Time-Delay Interferometric responses and estimated their sensitivities to vector- and scalar-type waves. We find that (i) at frequencies larger than roughly the inverse of the one-way light time ($\approx 6 \times 10ˆ{-2} $ Hz.) LISA is more than ten times sensitive to scalar-longitudinal and vector signals than to tensor and scalar-transverse waves, and (ii) in the low part of its frequency band is equally sensitive to tensor and vector waves and somewhat less sensitive to scalar signals.

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Dec 01, 2010

1010.1302 (/preprints)
2010-12-01, 13:38 [edit]

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