118385730
Testing general relativity using gravitational waves from binary neutron stars: Effect of spins
We present a Bayesian data analysis pipeline for testing GR using gravitational wave signals from coalescing compact binaries, and in particular binary neutron stars. In this study, we investigate its performance when sources with spins are taken into account.
1506194
TIGER: A data analysis pipeline for testing the strong-field dynamics of general relativity with gravitational wave signals from coalescing compact binaries
The direct detection of gravitational waves with upcoming second-generation gravitational wave observatories such as Advanced LIGO and Advanced Virgo will allow us to probe the genuinely strong-field dynamics of general relativity (GR) for the first time. We have developed a data analysis pipeline called TIGER (test infrastructure for general relativity), which uses signals from compact binary coalescences to perform a model-independent test of GR. In this paper we focus on signals from coalescing binary neutron stars, for which sufficiently accurate waveform models are already available which can be generated fast enough on a computer that they can be used in Bayesian inference. By performing numerical experiments in stationary, Gaussian noise, we show that for such systems, TIGER is robust against a number of unmodeled fundamental, astrophysical, and instrumental effects, such as differences between waveform approximants, a limited number of post-Newtonian phase contributions being known, the effects of neutron star tidal deformability on the orbital motion, neutron star spins, and instrumental calibration errors.
9403518
Measuring the spin of black holes in binary systems using gravitational waves.
Compact binary coalescences are the most promising sources of gravitational waves (GWs) for ground-based detectors. Binary systems containing one or two spinning black holes are particularly interesting due to spin-orbit (and eventual spin-spin) interactions and the opportunity of measuring spins directly through GW observations. In this Letter, we analyze simulated signals emitted by spinning binaries with several values of masses, spins, orientations, and signal-to-noise ratios, as detected by an advanced LIGO-Virgo network. We find that for moderate or high signal-to-noise ratio the spin magnitudes can be estimated with errors of a few percent (5%-30%) for neutron star-black hole (black hole-black hole) systems. Spins' tilt angle can be estimated with errors of 0.04 rad in the best cases, but typical values will be above 0.1 rad. Errors will be larger for signals barely above the threshold for detection. The difference in the azimuth angles of the spins, which may be used to check if spins are locked into resonant configurations, cannot be constrained. We observe that the best performances are obtained when the line of sight is perpendicular to the system's total angular momentum and that a sudden change of behavior occurs when a system is observed from angles such that the plane of the orbit can be seen both from above and below during the time the signal is in band. This study suggests that direct measurement of black hole spin by means of GWs can be as precise as what can be obtained from x-ray binaries.
120094772
Gravitational waves as deformations of embedded Einstein spaces
We show how approximate radiative solutions of Einstein's equations can be constructed using small deformations of Einstein spacetimes embedded into a pseudo-Euclidean flat space of higher dimension. Infinitesimal deformations are seen then as vector fields in EN. All geometrical quantities can be then expressed in terms of embedding functions zA and their deformations . Then we require the deformations to keep Einstein equations satisfied up to a given order in e. The system obtained is then analyzed in particular cases of the Minkowski and Schwarzschild manifolds taken as a starting point, and solutions of deformations of Einstein's equations displaying radiative behavior are found up to the third order of expansion in small parameter e.
59497924
Towards a generic test of the strong field dynamics of general relativity using compact binary coalescence: Further investigations
In this paper we elaborate on earlier work by the same authors in which a novel Bayesian inference framework for testing the strong-field dynamics of General Relativity using coalescing compact binaries was proposed. Unlike methods that were used previously, our technique addresses the question whether one or more 'testing coefficients' (e.g. in the phase) parameterizing deviations from GR are non-zero, rather than all of them differing from zero at the same time. The framework is well-adapted to a scenario where most sources have low signal-to-noise ratio, and information from multiple sources as seen in multiple detectors can readily be combined. In our previous work, we conjectured that this framework can detect generic deviations from GR that can in principle not be accomodated by our model waveforms, on condition that the change in phase near frequencies where the detectors are the most sensitive is comparable to that induced by simple shifts in the lower-order phase coefficients of more than a few percent (~ 5 radians at 150 Hz). To further support this claim, we perform additional numerical experiments in Gaussian and stationary noise according to the expected Advanced LIGO/Virgo noise curves, and coherently injecting signals into the network whose phasing differs structurally from the predictions of GR, but with the magnitude of the deviation still being small. We find that even then, a violation of GR can be established with good confidence.
118465419
Parameter estimation from gravitational waves generated by nonspinning binary black holes with laser interferometers: Beyond the Fisher information
In this paper we apply to gravitational waves from nonspinning binary systems a recently introduced frequentist methodology to calculate analytically the error for a maximum likelihood estimate of physical parameters. While existing literature focuses on using the Cramer Rao Lower bound and Monte Carlo simulations, we use a power expansion of the bias and covariance in inverse powers of the signal to noise ratio. The use of higher order derivatives of the likelihood function in the expansions makes the prediction also sensitive to the secondary lobes of the maximum likelihood estimate probability distribution. We discuss conditions for validity of the Cramer Rao Lower bound and predict new features in regions of the parameter space currently not explored. For example, we see how the bias can become the most important contributor to the parameters' errors for high mass systems (200M(circle dot) and above).
122404463
Calibration data diagnostic and data validation
This is a brief introductory overview to papers devoted to key steps in preparing data from Gravitational Wave detectors in view of a confident signal extraction.
122176893
Space-Time Metrology for the LISA Gravitational Wave Observatory, and Its Demonstration on LISA Pathfinder
The paper describes the key instrumental features of LISA, and discusses its limiting sources of uncertainty. It is shown how the basic element of LISA is a “Doppler link” where the frequency of a laser beam is compared by two far apart, free falling “observers”. These observers are two of the six LISA free falling test-masses. Each of the three LISA arms carries two such Doppler links, propagating along opposite directions. It is shown that a link like this acts as a time-delayed, differential accelerometer. Its performance is limited by three main sources of disturbance. Parasitic forces accelerate the test masses relative to their geodetic trajectories. Interferometry measurement noise is interpreted as relative motion of test-masses. Finally, because of intervening optical components fixed to spacecraft, the measurement is also corrupted by the relative acceleration of spacecraft and the test mass. We analyze these sources within a unifying picture, and show that LISA has a large “science margin”. Even with a sensitivity substantially poorer of what has been calculated, LISA remains a powerful astrophysics observatory.
84846704
LISA Pathfinder
M Armanoa, H Audleyb, J Bairdc, P Binetruy d,∗, M Bornb, D Bortoluzzie, E Castellif , A Cavallerif , A Cesarinig , A M Cruiseh, K Danzmannb, M de Deus Silvaa, I Diepholzb, G Dixonh, R Dolesif , L Ferraiolii, V Ferronif , E D Fitzsimonsj , M Freschia, L Gesak, F Gibertf , D Giardinii, R Giusterif , C Grimanig , J Grzymischl, I Harrisonm, G Heinzelb, M Hewitsonb, D Hollingtonc, D Hoylandh, M Huellerf , H Inchauspéd, O Jennrichl, P Jetzern, N Karnesisb, B Kauneb, N Korsakovao, C J Killowo, J A Lobok,†, I Llorok, L Liuf , J P López-Zaragozak, R Maarschalkerweerdm, D Mancei N Meshskari, V Mart́ınk, L Martin-Poloa, J Martinod, F Martin-Porquerasa, I Mateosk, P W McNamaral, J Mendesm, L Mendesa, M Nofrariask, S Paczkowskib?, M Perreur-Lloydo, A Petiteaud, P Pivatof , E Plagnold, J Ramos-Castrop, J Reicheb, D I Robertsono, F Rivask, G Russanof , J Slutskyq , C F Sopuertak, T Sumnerc, D Texiera, J I Thorpeq , D Vetrugnof , S Vitalef , G Wannerb, H Wardo, P Wassc,r, W J Weberf , L Wisselb, A Wittchenb, and P Zweifeli a European Space Astronomy Centre, European Space Agency, Villanueva de la Cañada, 28692 Madrid, Spain
118459662
Bayesian parameter estimation in the second LISA Pathfinder mock data challenge
A main scientific output of the LISA Pathfinder mission is to provide a noise model that can be extended to the future gravitational wave observatory, LISA. The success of the mission depends thus upon a deep understanding of the instrument, especially the ability to correctly determine the parameters of the underlying noise model. In this work we estimate the parameters of a simplified model of the LISA Technology Package instrument. We describe the LISA Technology Package by means of a closed-loop model that is used to generate the data, both injected signals and noise. Then, parameters are estimated using a Bayesian framework, and it is shown that this method reaches the optimal attainable error, the Cramer-Rao bound. We also address an important issue for the mission: how to efficiently combine the results of different experiments to obtain a unique set of parameters describing the instrument.
122288230
LISA Pathfinder test mass injection in geodesic motion: status of the on-ground testing
The LISA Technology Package (LTP) onboard the LISA Pathfinder mission aims to demonstrate, in orbit, several critical technology milestones for LISA, including the purest geodesic motion ever achieved for a macroscopic body. The gravitational reference sensor in the LTP hosts a heavy test mass (TM) surrounded by electrodes, at a relatively large 'gap' distance of several mm, which are used to measure and control the TM position and attitude. The large gaps-–necessary to minimize the force noise acting on the TM-–limit the available level of electrostatic actuation force that can be applied to the TM and thus the authority to control its position and velocity. Due to the large mass and gaps, a caging mechanism is required to securely hold the TM during the launch phase, when the whole payload endures large accelerations. Later in orbit, the TM must be injected into its geodesic trajectory, through the release from the caging mechanism and subsequent capture by the electrostatic actuation. During the release phase, the constraining device must limit adhesion forces that exert a net impulse upon rupture, such that the required forces needed to control the TM do not exceed the actuation authority. The TM injection into geodesic motion, and most critically the release phase, constitutes a potential point of failure for the mission. The on-ground verification of this phase is performed by measuring the momentum transferred between TM-representative surfaces and the release device, reproducing the dynamics that will take place in flight. This paper reports on the testing activities performed at the Department of Mechanical and Structural Engineering of the University of Trento.