120915791
Stochastic background detection with gravitational-wave resonant detectors
A linearized version of the standard Wiener filter theory is used to calculate the sensitivity to an isotropic stochastic gravitational-wave background of the AURIGA - NAUTILUS pair of ultra-low-temperature bar detectors, near to operating in coincidence in Italy, obtaining a sensitivity of . The addition of the VIRGO interferometric detector under construction in Italy improves the figure to . We also consider the pair formed by VIRGO and one large mass spherical detector located in a nearby available site in Italy and a pair of spherical detectors located at the AURIGA and NAUTILUS sites that promise to achieve sensitivities of .
119128106
Thermal gradient-induced forces on geodesic reference masses for LISA
The low frequency sensitivity of space-borne gravitational wave observatories will depend critically on the geodesic purity of the trajectories of orbiting test masses. Fluctuations in the temperature difference across the enclosure surrounding the free-falling test mass can produce noisy forces through several processes, including the radiometric effect, radiation pressure, and outgassing. We present here a detailed experimental investigation of thermal gradient-induced forces for the Laser Interferometer Space Antenna (LISA) gravitational wave mission and the LISA Pathfinder, employing high resolution torsion pendulum measurements of the torque on a LISA-like test mass suspended inside a prototype of the LISA gravitational reference sensor that will surround the test mass in orbit. The measurement campaign, accompanied by numerical simulations of the radiometric and radiation pressure effects, allows a more accurate and representative characterization of thermal-gradient forces in the specific geometry and environment relevant to LISA free-fall. The pressure dependence of the measured torques allows clear identification of the radiometric effect, in quantitative agreement with the model developed. In the limit of zero gas pressure, the measurements are most likely dominated by outgassing, but at a low level that does not threaten the current LISA noise estimate, which assumes a maximum net force per degreemore » of temperature difference of 100(pN/K) for the overall thermal gradient-induced effects.« less
36133266
From laboratory experiments to LISA Pathfinder: achieving LISA geodesic motion
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, 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 2 of the LISA requirement at 1 mHz and within a factor 6 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.
55218371
Brownian force noise from molecular collisions and the sensitivity of advanced gravitational wave observatories
We present an analysis of Brownian force noise from residual gas damping of reference test masses as a fundamental sensitivity limit in small force experiments. The resulting acceleration noise increases significantly when the distance of the test mass to the surrounding experimental apparatus is smaller than the dimension of the test mass itself. For the Advanced LIGO interferometric gravitational wave observatory, where the relevant test mass is a suspended 340 mm diameter cylindrical end mirror, the force noise power is increased by roughly a factor 40 by the presence of a similarly shaped reaction mass at a nominal separation of 5 mm. The force noise, of order 20 fN\rthz\ for $2 \times 10^{-6}$ Pa of residual H$_2$ gas, rivals quantum optical fluctuations as the dominant noise source between 10 and 30 Hz. We present here a numerical and analytical analysis for the gas damping force noise for Advanced LIGO, backed up by experimental evidence from several recent measurements. Finally, we discuss the impact of residual gas damping on the gravitational wave sensitivity and possible mitigation strategies.
63844509
The LISA Pathfinder interferometry-hardware and system testing
Preparations for the LISA Pathfinder mission have reached an exciting stage. Tests of the engineering model (EM) of the optical metrology system have recently been completed at the Albert Einstein Institute, Hannover, and flight model tests are now underway. Significantly, they represent the first complete integration and testing of the space-qualified hardware and are the first tests on an optical system level. The results and test procedures of these campaigns will be utilized directly in the ground-based flight hardware tests, and subsequently during in-flight operations. In addition, they allow valuable testing of the data analysis methods using the MATLAB-based LTP data analysis toolbox. This paper presents an overview of the results from the EM test campaign that was successfully completed in December 2009.
117102512
Towards an Ultracryogenic Bar Observatory for Gravitational Wave Bursts
122803437
Effect of calibration errors on Bayesian parameter estimation for gravitational wave signals from inspiral binary systems in the advanced detectors era: Further investigations
By 2015, the advanced versions of the gravitational wave detectors Virgo and LIGO will be online. They will collect data in coincidence with enough sensitivity to potentially deliver multiple detections of gravitational waves from inspirals of compact-object binaries. In a previous work, we have studied the effects introduced in the estimation of the physical parameters of the source by uncertainties in the calibration of the interferometers. Our bias estimator for parameter errors introduced by calibration uncertainties consisted of two terms: A genuine bias due to the calibration errors, and a contribution coming from the limited number of samples used to explore the parameter space. In this article, we have focused on this second term, and we have shown how it is smaller than the former (about 10 times smaller), and how it decreases as the signal-to-noise ratio increases.
17415632
Approximate solutions in General Relativity via deformation of embeddings
A systematic study of deformations of four-dimensional Einsteinian space-times embedded in a pseudo-Euclidean space E N of higher dimension is presented. Infinitesimal deformations, seen as vector fields in E N , can be divided in two parts, tangent to the embedded hypersurface and orthogonal to it; only the second ones are relevant, the tangent ones being equivalent to coordinate transformations in the embedded manifold. The geometrical quantities can be then expressed in terms of embedding functions z A and their infinitesimal deformations v A z A → ˜ z A = z A + e v A . The deformations are called Einsteinian if they keep Einstein equations satisfied up to a given order in e. The system so obtained is then analyzed in particular in the case of the Schwarzschild metric taken as the starting point, and some solutions of the first-order deformation of Einstein’s equations are found. We discuss also second and third order deformations leading to wave-like solutions and to the departure from spherical symmetry towards an axial one (the approximate Kerr solution) 1
55961759
How serious can the stealth bias be in gravitational wave parameter estimation
The upcoming direct detection of gravitational waves will open a window to probing the strong-field regime of general relativity. As a consequence, waveforms that include the presence of deviations from general relativity have been developed (e.g., in the parametrized post-Einsteinian approach). TIGER, a data analysis pipeline which builds Bayesian evidence to support or question the validity of general relativity, has been written and tested. In particular, it was shown that the LIGO and Virgo detectors can probe deviations from general relativity in a regime than cannot be tested by Solar System tests or pulsar timing measurements. However, evidence from several detections is required before a deviation from general relativity can be confidently claimed. An interesting consequence is that, should general relativity not be the correct theory of gravity in its strong field regime, using standard general relativity templates for the matched filter analysis of interferometer data will introduce biases in the gravitational wave measured parameters with potentially serious consequences on the astrophysical inferences, such as the coalescence rate or the mass distribution. In this work we consider three heuristic possible deviations from general relativity and show that the biases introduced in the estimated parameters of gravitational waves emitted during the inspiral phase of spinless compact binary coalescence systems assuming the validity of general relativity manifest in various ways. The mass parameters are usually the most affected, with biases that can be as large as 30 standard deviations for the symmetric mass ratio, and nearly one percent for the chirp mass, which is usually estimated with subpercent accuracy. Other parameters do not show a significant bias. We conclude that statements about the nature of the observed sources, e.g., if both objects are neutron stars, depend critically on the explicit assumption that general relativity is the right theory of gravity in the strong field regime.
119108663
Effect of calibration errors on Bayesian parameter estimation for gravitational wave signals from inspiral binary systems in the advanced detectors era
By 2015 the advanced versions of the gravitational-wave detectors Virgo and LIGO will be online. They will collect data in coincidence with enough sensitivity to potentially deliver multiple detections of gravitation waves from inspirals of compact-object binaries. This work is focused on understanding the effects introduced by uncertainties in the calibration of the interferometers. We consider plausible calibration errors based on estimates obtained during LIGO’s fifth and Virgo’s third science runs, which include frequency-dependent amplitude errors of 
∼ 
10 
% 
 and frequency-dependent phase errors of 
∼ 
3 
  
  
degrees 
 in each instrument. We quantify the consequences of such errors estimating the parameters of inspiraling binaries. We find that the systematics introduced by calibration errors on the inferred values of the chirp mass and mass ratio are smaller than 20% of the statistical measurement uncertainties in parameter estimation for 90% of signals in our mock catalog. Meanwhile, the calibration-induced systematics in the inferred sky location of the signal are smaller than 
∼ 
50 
% 
 of the statistical uncertainty. We thus conclude that calibration-induced errors at this level are not a significant detriment to accurate parameter estimation.
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.