1. 
 Abadie, J., et al.
(författare)

Implementation and testing of the first prompt search for gravitational wave transients with electromagnetic counterparts
 2012

Ingår i: Astronomy & Astrophysics.  : EDP Sciences.  00046361 . 14320746. ; 539

Tidskriftsartikel (refereegranskat)abstract
 Aims. A transient astrophysical event observed in both gravitational wave (GW) and electromagnetic (EM) channels would yield rich scientific rewards. A first program initiating EM followups to possible transient GW events has been developed and exercised by the LIGO and Virgo community in association with several partners. In this paper, we describe and evaluate the methods used to promptly identify and localize GW event candidates and to request images of targeted sky locations. Methods. During two observing periods (Dec. 17, 2009 to Jan. 8, 2010 and Sep. 2 to Oct. 20, 2010), a lowlatency analysis pipeline was used to identify GW event candidates and to reconstruct maps of possible sky locations. A catalog of nearby galaxies and Milky Way globular clusters was used to select the most promising sky positions to be imaged, and this directional information was delivered to EM observatories with time lags of about thirty minutes. A Monte Carlo simulation has been used to evaluate the lowlatency GW pipeline's ability to reconstruct source positions correctly. Results. For signals near the detection threshold, our lowlatency algorithms often localized simulated GW burst signals to tens of square degrees, while neutron star/neutron star inspirals and neutron star/black hole inspirals were localized to a few hundred square degrees. Localization precision improves for moderately stronger signals. The correct sky location of signals well above threshold and originating from nearby galaxies may be observed with similar to 50% or better probability with a few pointings of widefield telescopes.


2. 
 Abadie, J., et al.
(författare)

Search for Gravitational Waves Associated with GammaRay Bursts during LIGO Science Run 6 and Virgo Science Runs 2 and 3
 2012

Ingår i: Astrophysical Journal.  0004637X. ; 760:1

Tidskriftsartikel (refereegranskat)abstract
 We present the results of a search for gravitational waves associated with 154 gammaray bursts (GRBs) that were detected by satellitebased gammaray experiments in 20092010, during the sixth LIGO science run and the second and third Virgo science runs. We perform two distinct searches: a modeled search for coalescences of either two neutron stars or a neutron star and black hole, and a search for generic, unmodeled gravitationalwave bursts. We find no evidence for gravitationalwave counterparts, either with any individual GRB in this sample or with the population as a whole. For all GRBs we place lower bounds on the distance to the progenitor, under the optimistic assumption of a gravitationalwave emission energy of 10(2) Mcircle dot c(2) at 150 Hz, with a median limit of 17 Mpc. For shorthard GRBs we place exclusion distances on binary neutron star and neutronstarblackhole progenitors, using astrophysically motivated priors on the source parameters, with median values of 16 Mpc and 28 Mpc, respectively. These distance limits, while significantly larger than for a search that is not aided by GRB satellite observations, are not large enough to expect a coincidence with a GRB. However, projecting these exclusions to the sensitivities of Advanced LIGO and Virgo, which should begin operation in 2015, we find that the detection of gravitational waves associated with GRBs will become quite possible.


3. 
 Abadie, J., et al.
(författare)

Allsky search for gravitationalwave bursts in the second joint LIGOVirgo run
 2012

Ingår i: Physical Review D (Particles, Fields, Gravitation and Cosmology).  15502368. ; 85:12

Tidskriftsartikel (refereegranskat)abstract
 We present results from a search for gravitationalwave bursts in the data collected by the LIGO and Virgo detectors between July 7, 2009 and October 20, 2010: data are analyzed when at least two of the three LIGOVirgo detectors are in coincident operation, with a total observation time of 207 days. The analysis searches for transients of duration less than or similar to 1 s over the frequency band 645000 Hz, without other assumptions on the signal waveform, polarization, direction or occurrence time. All identified events are consistent with the expected accidental background. We set frequentist upper limits on the rate of gravitationalwave bursts by combining this search with the previous LIGOVirgo search on the data collected between November 2005 and October 2007. The upper limit on the rate of strong gravitationalwave bursts at the Earth is 1.3 events per year at 90% confidence. We also present upper limits on source rate density per year and Mpc(3) for sample populations of standardcandle sources. As in the previous joint run, typical sensitivities of the search in terms of the rootsumsquared strain amplitude for these waveforms lie in the range similar to 5 x 10(22) Hz(1/2) to similar to 1 x 10(20) Hz(1/2). The combination of the two joint runs entails the most sensitive allsky search for generic gravitationalwave bursts and synthesizes the results achieved by the initial generation of interferometric detectors.


4. 
 Abadie, J., et al.
(författare)

First lowlatency LIGO plus Virgo search for binary inspirals and their electromagnetic counterparts
 2012

Ingår i: Astronomy & Astrophysics.  : EDP Sciences.  00046361 . 14320746. ; 541

Tidskriftsartikel (refereegranskat)abstract
 Aims. The detection and measurement of gravitationalwaves from coalescing neutronstar binary systems is an important science goal for groundbased gravitationalwave detectors. In addition to emitting gravitationalwaves at frequencies that span the most sensitive bands of the LIGO and Virgo detectors, these sources are also amongst the most likely to produce an electromagnetic counterpart to the gravitationalwave emission. A joint detection of the gravitationalwave and electromagnetic signals would provide a powerful new probe for astronomy. Methods. During the period between September 19 and October 20, 2010, the first lowlatency search for gravitationalwaves from binary inspirals in LIGO and Virgo data was conducted. The resulting triggers were sent to electromagnetic observatories for followup. We describe the generation and processing of the lowlatency gravitationalwave triggers. The results of the electromagnetic image analysis will be described elsewhere. Results. Over the course of the science run, three gravitationalwave triggers passed all of the lowlatency selection cuts. Of these, one was followed up by several of our observational partners. Analysis of the gravitationalwave data leads to an estimated false alarm rate of once every 6.4 days, falling far short of the requirement for a detection based solely on gravitationalwave data.


5. 
 Abadie, J., et al.
(författare)

Upper limits on a stochastic gravitationalwave background using LIGO and Virgo interferometers at 6001000 Hz
 2012

Ingår i: Physical Review D (Particles, Fields, Gravitation and Cosmology).  15502368. ; 85:12

Tidskriftsartikel (refereegranskat)abstract
 A stochastic background of gravitational waves is expected to arise from a superposition of many incoherent sources of gravitational waves, of either cosmological or astrophysical origin. This background is a target for the current generation of groundbased detectors. In this article we present the first joint search for a stochastic background using data from the LIGO and Virgo interferometers. In a frequency band of 6001000 Hz, we obtained a 95% upper limit on the amplitude of Omega(GW)(f) = Omega(3)(f/900 Hz)(3), of Omega(3) < 0.32, assuming a value of the Hubble parameter of h(100) = 0.71. These new limits are a factor of seven better than the previous best in this frequency band.


6. 
 Abadie, J., et al.
(författare)

Search for gravitational waves from intermediate mass binary black holes
 2012

Ingår i: Physical Review D (Particles, Fields, Gravitation and Cosmology).  15502368. ; 85:10

Tidskriftsartikel (refereegranskat)abstract
 We present the results of a weakly modeled burst search for gravitational waves from mergers of nonspinning intermediate mass black holes in the total mass range 100450 Mcircle dot and with the component mass ratios between 1: and 4:1. The search was conducted on data collected by the LIGO and Virgo detectors between November of 2005 and October of 2007. No plausible signals were observed by the search which constrains the astrophysical rates of the intermediate mass black holes mergers as a function of the component masses. In the most efficiently detected bin centered on 88 + 88 Mcircle dot, for nonspinning sources, the rate density upper limit is 0.13 per Mpc(3) per Myr at the 90% confidence level.


7. 
 Abadie, J., et al.
(författare)

Search for gravitational waves from low mass compact binary coalescence in LIGO's sixth science run and Virgo's science runs 2 and 3
 2012

Ingår i: Physical Review D (Particles, Fields, Gravitation and Cosmology).  15502368. ; 85:8

Tidskriftsartikel (refereegranskat)abstract
 We report on a search for gravitational waves from coalescing compact binaries using LIGO and Virgo observations between July 7, 2009, and October 20, 2010. We searched for signals from binaries with total mass between 2 and 25M(circle dot); this includes binary neutron stars, binary black holes, and binaries consisting of a black hole and neutron star. The detectors were sensitive to systems up to 40 Mpc distant for binary neutron stars, and further for higher mass systems. No gravitationalwave signals were detected. We report upper limits on the rate of compact binary coalescence as a function of total mass, including the results from previous LIGO and Virgo observations. The cumulative 90% confidence rate upper limits of the binary coalescence of binary neutron star, neutron starblack hole, and binary black hole systems are 1.3 x 10(4), 3.1 x 10(5), and 6.4 x 10(6) Mpc(3) yr(1), respectively. These upper limits are up to a factor 1.4 lower than previously derived limits. We also report on results from a blind injection challenge.


8. 
 Abadie, J., et al.
(författare)

Allsky search for periodic gravitational waves in the full S5 LIGO data
 2012

Ingår i: Physical Review D (Particles, Fields, Gravitation and Cosmology).  15502368. ; 85:2

Tidskriftsartikel (refereegranskat)abstract
 We report on an allsky search for periodic gravitational waves in the frequency band 50800 Hz and with the frequency time derivative in the range of 0 through 6 x 10(9) Hz/s. Such a signal could be produced by a nearby spinning and slightly nonaxisymmetric isolated neutron star in our Galaxy. After recent improvements in the search program that yielded a 10x increase in computational efficiency, we have searched in two years of data collected during LIGO's fifth science run and have obtained the most sensitive allsky upper limits on gravitationalwave strain to date. Near 150 Hz our upper limit on worstcase linearly polarized strain amplitude h(0) is 1 x 10(24), while at the high end of our frequency range we achieve a worstcase upper limit of 3.8 x 10(24) for all polarizations and sky locations. These results constitute a factor of 2 improvement upon previously published data. A new detection pipeline utilizing a loosely coherent algorithm was able to follow up weaker outliers, increasing the volume of space where signals can be detected by a factor of 10, but has not revealed any gravitationalwave signals. The pipeline has been tested for robustness with respect to deviations from the model of an isolated neutron star, such as caused by a lowmass or longperiod binary companion.


9. 
 Ade, P. A. R., et al.
(författare)

Planck 2015 results XIV. Dark energy and modified gravity
 2016

Ingår i: Astronomy and Astrophysics.  : EDP Sciences.  00046361 . 14320746. ; 594

Tidskriftsartikel (refereegranskat)abstract
 We study the implications of Planck data for models of dark energy (DE) and modified gravity (MG) beyond the standard cosmological constant scenario. We start with cases where the DE only directly affects the background evolution, considering Taylor expansions of the equation of state w(a), as well as principal component analysis and parameterizations related to the potential of a minimally coupled DE scalar field. When estimating the density of DE at early times, we significantly improve present constraints and find that it has to be below similar to 2% (at 95% confidence) of the critical density, even when forced to play a role for z < 50 only. We then move to general parameterizations of the DE or MG perturbations that encompass both effective field theories and the phenomenology of gravitational potentials in MG models. Lastly, we test a range of specific models, such as kessence, f(R) theories, and coupled DE. In addition to the latest Planck data, for our main analyses, we use background constraints from baryonic acoustic oscillations, typeIa supernovae, and local measurements of the Hubble constant. We further show the impact of measurements of the cosmological perturbations, such as redshiftspace distortions and weak gravitational lensing. These additional probes are important tools for testing MG models and for breaking degeneracies that are still present in the combination of Planck and background data sets. All results that include only background parameterizations (expansion of the equation of state, early DE, general potentials in minimallycoupled scalar fields or principal component analysis) are in agreement with ACDM. When testing models that also change perturbations (even when the background is fixed to ACDM), some tensions appear in a few scenarios: the maximum one found is similar to 2 sigma for Planck TT + lowP when parameterizing observables related to the gravitational potentials with a chosen time dependence; the tension increases to, at most, 3 sigma when external data sets are included. It however disappears when including CMB lensing.


10. 
 Ade, P. A. R., et al.
(författare)

Planck 2015 results XX. Constraints on inflation
 2016

Ingår i: Astronomy and Astrophysics.  : EDP Sciences.  00046361 . 14320746. ; 594

Tidskriftsartikel (refereegranskat)abstract
 We present the implications for cosmic inflation of the Planck measurements of the cosmic microwave background (CMB) anisotropies in both temperature and polarization based on the full Planck survey, which includes more than twice the integration time of the nominal survey used for the 2013 release papers. The Planck full mission temperature data and a first release of polarization data on large angular scales measure the spectral index of curvature perturbations to be n(s) = 0.968 +/ 0.006 and tightly constrain its scale dependence to dn(s)/dln k = 0.003 +/ 0.007 when combined with the Planck lensing likelihood. When the Planck highl polarization data are included, the results are consistent and uncertainties are further reduced. The upper bound on the tensortoscalar ratio is r(0).(002) < 0.11 (95% CL). This upper limit is consistent with the Bmode polarization constraint r < 0.12 (95% CL) obtained from a joint analysis of the BICEP2/Keck Array and Planck data. These results imply that V(phi) proportional to phi(2) and natural inflation are now disfavoured compared to models predicting a smaller tensortoscalar ratio, such as R2 inflation. We search for several physically motivated deviations from a simple powerlaw spectrum of curvature perturbations, including those motivated by a reconstruction of the inflaton potential not relying on the slowroll approximation. We find that such models are not preferred, either according to a Bayesian model comparison or according to a frequentist simulationbased analysis. Three independent methods reconstructing the primordial power spectrum consistently recover a featureless and smooth PR (k) over the range of scales 0.008 Mpc(1) less than or similar to k less than or similar to 0.1 Mpc(1). At large scales, each method finds deviations from a power law, connected to a deficit at multipoles l approximate to 2040 in the temperature power spectrum, but at an uncompelling statistical significance owing to the large cosmic variance present at these multipoles. By combining power spectrum and nonGaussianity bounds, we constrain models with generalized Lagrangians, including Galileon models and axion monodromy models. The Planck data are consistent with adiabatic primordial perturbations, and the estimated values for the parameters of the base Lambda cold dark matter (Lambda CDM) model are not significantly altered when more general initial conditions are admitted. In correlated mixed adiabatic and isocurvature models, the 95% CL upper bound for the nonadiabatic contribution to the observed CMB temperature variance is vertical bar alpha(nonadi)vertical bar < 1.9%, 4.0%, and 2.9% for CDM, neutrino density, and neutrino velocity isocurvature modes, respectively. We have tested inflationary models producing an anisotropic modulation of the primordial curvature power spectrum finding that the dipolar modulation in the CMB temperature field induced by a CDM isocurvature perturbation is not preferred at a statistically significant level. We also establish tight constraints on a possible quadrupolar modulation of the curvature perturbation. These results are consistent with the Planck 2013 analysis based on the nominal mission data and further constrain slowroll singlefield inflationary models, as expected from the increased precision of Planck data using the full set of observations.

