Publications (345)1200.31 Total impact
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ABSTRACT: We present the results of a search for longduration gravitational wave transients in two sets of data collected by the LIGO Hanford and LIGO Livingston detectors between November 5, 2005 and September 30, 2007, and July 7, 2009 and October 20, 2010, with a total observational time of 283.0 days and 132.9 days, respectively. The search targets gravitational wave transients of duration 10  500 seconds in a frequency band of 40  1000 Hz, with minimal assumptions about the signal waveform, polarization, source direction, or time of occurrence. All candidate triggers were consistent with the expected background; as a result we set 90% confidence upper limits on the rate of longduration gravitational wave transients for different types of gravitational wave signals. We also report upper limits on the source rate density per year per Mpc^3 for specific signal models. These are the first results from an allsky search for unmodeled longduration transient gravitational waves.  [Show abstract] [Hide abstract]
ABSTRACT: In this paper we present the results of the first low frequency allsky search of continuous gravitational wave signals conducted on Virgo VSR2 and VSR4 data. The search covered the full sky, a frequency range between 20 Hz and 128 Hz with a range of spindown between $1.0 \times 10^{10}$ Hz/s and $+1.5 \times 10^{11}$ Hz/s, and was based on a hierarchical approach. The starting point was a set of short Fast Fourier Transforms (FFT), of length 8192 seconds, built from the calibrated strain data. Aggressive data cleaning, both in the time and frequency domains, has been done in order to remove, as much as possible, the effect of disturbances of instrumental origin. On each dataset a number of candidates has been selected, using the FrequencyHough transform in an incoherent step. Only coincident candidates among VSR2 and VSR4 have been examined in order to strongly reduce the false alarm probability, and the most significant candidates have been selected. The criteria we have used for candidate selection and for the coincidence step greatly reduce the harmful effect of large instrumental artifacts. Selected candidates have been subject to a followup by constructing a new set of longer FFTs followed by a further incoherent analysis. No evidence for continuous gravitational wave signals was found, therefore we have set a populationbased joint VSR2VSR4 90$\%$ confidence level upper limit on the dimensionless gravitational wave strain in the frequency range between 20 Hz and 128 Hz. This is the first allsky search for continuous gravitational waves conducted at frequencies below 50 Hz. We set upper limits in the range between about $10^{24}$ and $2\times 10^{23}$ at most frequencies. Our upper limits on signal strain show an improvement of up to a factor of $\sim$2 with respect to the results of previous allsky searches at frequencies below $80~\mathrm{Hz}$.  [Show abstract] [Hide abstract]
ABSTRACT: We report results of a wideband search for periodic gravitational waves from isolated neutron stars within the Orion spur towards both the inner and outer regions of our Galaxy. As gravitational waves interact very weakly with matter, the search is unimpeded by dust and concentrations of stars. One search disk (A) is $6.87^\circ$ in diameter and centered on $20^\textrm{h}10^\textrm{m}54.71^\textrm{s}+33^\circ33'25.29"$, and the other (B) is $7.45^\circ$ in diameter and centered on $8^\textrm{h}35^\textrm{m}20.61^\textrm{s}46^\circ49'25.151"$. We explored the frequency range of 501500 Hz and frequency derivative from $0$ to $5\times 10^{9}$ Hz/s. A multistage, loosely coherent search program allowed probing more deeply than before in these two regions, while increasing coherence length with every stage. Rigorous followup parameters have winnowed initial coincidence set to only 70 candidates, to be examined manually. None of those 70 candidates proved to be consistent with an isolated gravitational wave emitter, and 95% confidence level upper limits were placed on continuouswave strain amplitudes. Near $169$ Hz we achieve our lowest 95% CL upper limit on worstcase linearly polarized strain amplitude $h_0$ of $6.3\times 10^{25}$, while at the high end of our frequency range we achieve a worstcase upper limit of $3.4\times 10^{24}$ for all polarizations and sky locations. 


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ABSTRACT: We present the first numericalrelativity simulation of a compactobject binary whose gravitational waveform is long enough to cover the entire frequency band of advanced gravitationalwave detectors, such as LIGO, Virgo and KAGRA, for mass ratio 7 and total mass as low as 45.5M_☉. We find that effectiveonebody models, either uncalibrated or calibrated against substantially shorter numericalrelativity waveforms at smaller mass ratios, reproduce our new waveform remarkably well, with a negligible loss in detection rate due to modeling error. In contrast, postNewtonian inspiral waveforms and existing calibrated phenomenological inspiralmergerringdown waveforms display greater disagreement with our new simulation. The disagreement varies substantially depending on the specific postNewtonian approximant used. 
Article: The Missing Link: Bayesian Detection and Measurement of IntermediateMass BlackHole Binaries
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ABSTRACT: We perform Bayesian analysis of gravitationalwave signals from nonspinning, intermediatemass blackhole binaries (IMBHBs) with observed total mass, $M_{\mathrm{obs}}$, from $50\mathrm{M}_{\odot}$ to $500\mathrm{M}_{\odot}$ and mass ratio $1\mbox{}4$ using advanced LIGO and Virgo detectors. We employ inspiralmergerringdown waveform models based on the effectiveonebody formalism and include subleading modes of radiation beyond the leading $(2,2)$ mode. The presence of subleading modes increases signal power for inclined binaries and allows for improved accuracy and precision in measurements of the masses as well as breaking of extrinsic parameter degeneracies. For low total masses, $M_{\mathrm{obs}} \lesssim 50 \mathrm{M}_{\odot}$, the observed chirp mass $\mathcal{M}_{\rm obs} = M_{\mathrm{obs}}\,\eta^{3/5}$ ($\eta$ being the symmetric mass ratio) is better measured. In contrast, as increasing power comes from merger and ringdown, we find that the total mass $M_{\mathrm{obs}}$ has better relative precision than $\mathcal{M}_{\rm obs}$. Indeed, at high $M_{\mathrm{obs}}$ ($\geq 300 \mathrm{M}_{\odot}$), the signal resembles a burst and the measurement thus extracts the dominant frequency of the signal that depends on $M_{\mathrm{obs}}$. Depending on the binary's inclination, at signaltonoise ratio (SNR) of $12$, uncertainties in $M_{\mathrm{obs}}$ can be as large as $\sim 20 \mbox{}25\%$ while uncertainties in $\mathcal{M}_{\rm obs}$ are $\sim 50 \mbox{}60\%$ in binaries with unequal masses (those numbers become $\sim 17\%$ versus $\sim22\%$ in more symmetric binaries). Although large, those uncertainties will establish the existence of IMBHs. Our results show that gravitationalwave observations can offer a unique tool to observe and understand the formation, evolution and demographics of IMBHs, which are difficult to observe in the electromagnetic window. (abridged) 
Article: Advanced LIGO
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ABSTRACT: The Advanced LIGO gravitational wave detectors are secondgeneration instruments designed and built for the two LIGO observatories in Hanford, WA and Livingston, LA, USA. The two instruments are identical in design, and are specialized versions of a Michelson interferometer with 4 km long arms. As in Initial LIGO, Fabry–Perot cavities are used in the arms to increase the interaction time with a gravitational wave, and power recycling is used to increase the effective laser power. Signal recycling has been added in Advanced LIGO to improve the frequency response. In the most sensitive frequency region around 100 Hz, the design strain sensitivity is a factor of 10 better than Initial LIGO. In addition, the low frequency end of the sensitivity band is moved from 40 Hz down to 10 Hz. All interferometer components have been replaced with improved technologies to achieve this sensitivity gain. Much better seismic isolation and test mass suspensions are responsible for the gains at lower frequencies. Higher laser power, larger test masses and improved mirror coatings lead to the improved sensitivity at mid and high frequencies. Data collecting runs with these new instruments are planned to begin in mid2015.  [Show abstract] [Hide abstract]
ABSTRACT: We present the first numericalrelativity simulation of a compactobject binary whose gravitational waveform is long enough to cover the entire frequency band of advanced gravitationalwave detectors, such as LIGO, Virgo and KAGRA, for mass ratio 7 and total mass as low as $45.5\,M_\odot$. We find that effectiveonebody models, either uncalibrated or calibrated against substantially shorter numericalrelativity waveforms at smaller mass ratios, reproduce our new waveform remarkably well, with a negligible loss in detection rate due to modeling error. In contrast, postNewtonian inspiral waveforms and existing calibrated phenomenological inspiralmergerringdown waveforms display greater disagreement with our new simulation. The disagreement varies substantially depending on the specific postNewtonian approximant used.  [Show abstract] [Hide abstract]
ABSTRACT: We describe directed searches for continuous gravitational waves in data from the sixth LIGO science data run. The targets were nine young supernova remnants not associated with pulsars; eight of the remnants are associated with nonpulsing suspected neutron stars. One target's parameters are uncertain enough to warrant two searches, for a total of ten. Each search covered a broad band of frequencies and first and second frequency derivatives for a fixed sky direction. The searches coherently integrated data from the two LIGO interferometers over time spans from 5.325.3 days using the matchedfiltering Fstatistic. We found no credible gravitationalwave signals. We set 95% confidence upper limits as strong (low) as $4\times10^{25}$ on intrinsic strain, $2\times10^{7}$ on fiducial ellipticity, and $4\times10^{5}$ on rmode amplitude. These beat the indirect limits from energy conservation and are within the range of theoretical predictions for neutronstar ellipticities and rmode amplitudes.  [Show abstract] [Hide abstract]
ABSTRACT: We present results of a search for continuouslyemitted gravitational radiation, directed at the brightest lowmass Xray binary, Scorpius X1. Our semicoherent analysis covers 10 days of LIGO S5 data ranging from 50550 Hz, and performs an incoherent sum of coherent $\mathcal{F}$statistic power distributed amongst frequencymodulated orbital sidebands. All candidates not removed at the veto stage were found to be consistent with noise at a 1% false alarm rate. We present Bayesian 95% confidence upper limits on gravitationalwave strain amplitude using two different prior distributions: a standard one, with no a priori assumptions about the orientation of Scorpius X1; and an anglerestricted one, using a prior derived from electromagnetic observations. Median strain upper limits of 1.3e24 and 8e25 are reported at 150 Hz for the standard and anglerestricted searches respectively. This proof of principle analysis was limited to a short observation time by unknown effects of accretion on the intrinsic spin frequency of the neutron star, but improves upon previous upper limits by factors of ~1.4 for the standard, and 2.3 for the anglerestricted search at the sensitive region of the detector.  [Show abstract] [Hide abstract]
ABSTRACT: We report the results of a multimessenger search for coincident signals from the LIGO and Virgo gravitationalwave observatories and the partially completed IceCube highenergy neutrino detector, including periods of joint operation between 20072010. These include parts of the 20052007 run and the 20092010 run for LIGOVirgo, and IceCube's observation periods with 22, 59 and 79 strings. We find no significant coincident events, and use the search results to derive upper limits on the rate of joint sources for a range of source emission parameters. For the optimistic assumption of gravitationalwave emission energy of $10^{2}$ M$_\odot$c$^2$ at $\sim 150$ Hz with $\sim 60$ ms duration, and highenergy neutrino emission of $10^{51}$ erg comparable to the isotropic gammaray energy of gammaray bursts, we limit the source rate below $1.6 \times 10^{2}$ Mpc$^{3}$yr$^{1}$. We also examine how combining information from gravitational waves and neutrinos will aid discovery in the advanced gravitationalwave detector era.  [Show abstract] [Hide abstract]
ABSTRACT: In this paper we present the results of a coherent narrowband search for continuous gravitationalwave signals from the Crab and Vela pulsars conducted on Virgo VSR4 data. In order to take into account a possible small mismatch between the gravitational wave frequency and two times the star rotation frequency, inferred from measurement of the electromagnetic pulse rate, a range of 0.02 Hz around two times the star rotational frequency has been searched for both the pulsars. No evidence for a signal has been found and 95$\%$ confidence level upper limits have been computed both assuming polarization parameters are completely unknown and that they are known with some uncertainty, as derived from Xray observations of the pulsar wind torii. For Vela the upper limits are comparable to the spindown limit, computed assuming that all the observed spindown is due to the emission of gravitational waves. For Crab the upper limits are about a factor of two below the spindown limit, and represent a significant improvement with respect to past analysis. This is the first time the spindown limit is significantly overcome in a narrowband search.  [Show abstract] [Hide abstract]
ABSTRACT: In 20092010, the Laser Interferometer Gravitationalwave Observa tory (LIGO) operated together with international partners Virgo and GEO600 as a network to search for gravitational waves of astrophysical origin. The sensitiv ity of these detectors was limited by a combination of noise sources inherent to the instrumental design and its environment, often localized in time or frequency, that couple into the gravitationalwave readout. Here we review the performance of the LIGO instruments during this epoch, the work done to characterize the de tectors and their data, and the effect that transient and continuous noise artefacts have on the sensitivity of LIGO to a variety of astrophysical sources.  [Show abstract] [Hide abstract]
ABSTRACT: Gravitationalwave astronomy will soon become a new tool for observing the Universe. Detecting and interpreting gravitational waves will require deep theoretical insights into astronomical sources. The past three decades have seen remarkable progress in analytical and numerical computations of the source dynamics, development of search algorithms and analysis of data from detectors with unprecedented sensitivity. This Chapter is devoted to examine the advances and future challenges in understanding the dynamics of binary and isolated compactobject systems, expected cosmological sources, their amplitudes and rates, and highlights of results from gravitationalwave observations. All of this is a testament to the readiness of the community to open a new window for observing the cosmos, a century after gravitational waves were first predicted by Albert Einstein.  [Show abstract] [Hide abstract]
ABSTRACT: Searches for a stochastic gravitationalwave background (SGWB) using terrestrial detectors typically involve crosscorrelating data from pairs of detectors. The sensitivity of such crosscorrelation analyses depends, among other things, on the separation between the two detectors: the smaller the separation, the better the sensitivity. Hence, a colocated detector pair is more sensitive to a gravitationalwave background than a noncolocated detector pair. However, colocated detectors are also expected to suffer from correlated noise from instrumental and environmental effects that could contaminate the measurement of the background. Hence, methods to identify and mitigate the effects of correlated noise are necessary to achieve the potential increase in sensitivity of colocated detectors. Here we report on the first SGWB analysis using the two LIGO Hanford detectors and address the complications arising from correlated environmental noise. We apply correlated noise identification and mitigation techniques to data taken by the two LIGO Hanford detectors, H1 and H2, during LIGO's fifth science run. At low frequencies, 40  460 Hz, we are unable to sufficiently mitigate the correlated noise to a level where we may confidently measure or bound the stochastic gravitationalwave signal. However, at high frequencies, 4601000 Hz, these techniques are sufficient to set a $95\%$ confidence level (C.L.) upper limit on the gravitationalwave energy density of \Omega(f)<7.7 x 10^{4} (f/ 900 Hz)^3, which improves on the previous upper limit by a factor of $\sim 180$. In doing so, we demonstrate techniques that will be useful for future searches using advanced detectors, where correlated noise (e.g., from global magnetic fields) may affect even widely separated detectors.  [Show abstract] [Hide abstract]
ABSTRACT: We calculate quasiequilibrium sequences of equalmass, irrotational binary neutron stars (BNSs) in a scalartensor (ST) theory of gravity that admits dynamical scalarization. We model neutron stars with realistic equations of state (notably through piecewise polytropic equations of state). Using these quasiequilibrium sequences we compute the binary's scalar charge and binding energy versus orbital angular frequency. We find that the absolute value of the binding energy is smaller than in general relativity (GR), differing at most by ~14% at high frequencies for the cases considered. We use the newly computed binding energy and the balance equation to estimate the number of gravitationalwave (GW) cycles during the adiabatic, quasicircular inspiral stage up to the end of the sequence, which is the last stable orbit or the mass shedding point, depending on which comes first. We find that, depending on the ST parameters, the number of GW cycles can be substantially smaller than in GR. In particular, we obtain that when dynamical scalarization sets in around a GW frequency of ~130 Hz, the sole inclusion of the ST binding energy causes a reduction of GW cycles from ~120 Hz up to the end of the sequence (~1200 Hz) of ~11% with respect to the GR case. We estimate that when the ST energy flux is also included the reduction in GW cycles becomes of ~24%. Quite interestingly, dynamical scalarization can produce a difference in the number of GW cycles with respect to the GR pointparticle case that is much larger than the effect due to tidal interactions, which is on the order of only a few GW cycles. These results further clarify and confirm recent studies that have evolved BNSs either in full numerical relativity or in postNewtonian theory, and point out the importance of developing accurate STtheory waveforms for systems composed of strongly selfgravitating objects, such as BNSs. 
Article: Search for Gravitational Waves Associated with γ ray Bursts Detected by the Interplanetary Network
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ABSTRACT: We present the results of a search for gravitational waves associated with 223 gammaray bursts (GRBs) detected by the InterPlanetary Network (IPN) in 20052010 during LIGO's fifth and sixth science runs and Virgo's first, second and third science runs. The IPN satellites provide accurate times of the bursts and sky localizations that vary significantly from degree scale to hundreds of square degrees. We search for both a wellmodeled binary coalescence signal, the favored progenitor model for short GRBs, and for generic, unmodeled gravitational wave bursts. Both searches use the event time and sky localization to improve the gravitationalwave search sensitivity as compared to corresponding alltime, allsky searches. We find no evidence of a gravitationalwave signal associated with any of the IPN GRBs in the sample, nor do we find evidence for a population of weak gravitationalwave signals associated with the GRBs. For all IPNdetected GRBs, for which a sufficient duration of quality gravitationalwave data is available, we place lower bounds on the distance to the source in accordance with an optimistic assumption of gravitationalwave emission energy of $10^{2}M_{\odot}c^2$ at 150 Hz, and find a median of 13 Mpc. For the 27 shorthard GRBs we place 90% confidence exclusion distances to two source models: a binary neutron star coalescence, with a median distance of 12Mpc, or the coalescence of a neutron star and black hole, with a median distance of 22 Mpc. Finally, we combine this search with previously published results to provide a population statement for GRB searches in firstgeneration LIGO and Virgo gravitationalwave detectors, and a resulting examination of prospects for the advanced gravitationalwave detectors.  [Show abstract] [Hide abstract]
ABSTRACT: Gravitational waves from a variety of sources are predicted to superpose to create a stochastic background. This background is expected to contain unique information from throughout the history of the universe that is unavailable through standard electromagnetic observations, making its study of fundamental importance to understanding the evolution of the universe. We carry out a search for the stochastic background with the latest data from LIGO and Virgo. Consistent with predictions from most stochastic gravitationalwave background models, the data display no evidence of a stochastic gravitationalwave signal. Assuming a gravitationalwave spectrum of Omega_GW(f)=Omega_alpha*(f/f_ref)^alpha, we place 95% confidence level upper limits on the energy density of the background in each of four frequency bands spanning 41.51726 Hz. In the frequency band of 41.5169.25 Hz for a spectral index of alpha=0, we constrain the energy density of the stochastic background to be Omega_GW(f)<5.6x10^6. For the 6001000 Hz band, Omega_GW(f)<0.14*(f/900 Hz)^3, a factor of 2.5 lower than the best previously reported upper limits. We find Omega_GW(f)<1.8x10^4 using a spectral index of zero for 170600 Hz and Omega_GW(f)<1.0*(f/1300 Hz)^3 for 10001726 Hz, bands in which no previous direct limits have been placed. The limits in these four bands are the lowest direct measurements to date on the stochastic background. We discuss the implications of these results in light of the recent claim by the BICEP2 experiment of the detection of inflationary gravitational waves.
Publication Stats
11k  Citations  
1,200.31  Total Impact Points  
Top Journals
Institutions

20082015

Loyola University Maryland
Baltimore, Maryland, United States 
Università degli Studi di Salerno
Fisciano, Campania, Italy 
NASA
Вашингтон, West Virginia, United States


19702015

University of Maryland, College Park
 Department of Physics
CGS, Maryland, United States


2014

University of Texas at Brownsville and Texas Southmost College
Brownsville, Texas, United States 
University of NiceSophia Antipolis
Nice, ProvenceAlpesCôte d'Azur, France


2013

Canadian Institute For Advanced Research
Toronto, Ontario, Canada


2012

Pierre and Marie Curie University  Paris 6
 Laboratoire KastlerBrossel (LKB)
Lutetia Parisorum, ÎledeFrance, France


20112012

Harvard University
 Radcliffe Institute for Advanced Study
Cambridge, Massachusetts, United States


2010

VU University Amsterdam
Amsterdamo, North Holland, Netherlands


20082009

Stanford University
 E. L. Ginzton Laboratory
Palo Alto, California, United States


20002006

California Institute of Technology
 • Department of Physics
 • Jet Propulsion Laboratory
 • Division of Physics, Mathematics, and Astronomy
Pasadena, California, United States


2005

French National Centre for Scientific Research
 Institut d'astrophysique spatiale (IAS)
Lutetia Parisorum, ÎledeFrance, France


20032005

Institut d'astrophysique de Paris
Lutetia Parisorum, ÎledeFrance, France 
Massachusetts Institute of Technology
Cambridge, Massachusetts, United States


2004

University of Birmingham
 School of Physics and Astronomy
Birmingham, England, United Kingdom 
Carleton College
نورثفیلد، مینهسوتا, Minnesota, United States


1998

Institut des Hautes Études Scientifiques
BuresOrsay, ÎledeFrance, France


1997

CERN
 Theoretical Physics Unit (TH)
Genève, Geneva, Switzerland


19951997

Università di Pisa
Pisa, Tuscany, Italy 
INFN  Istituto Nazionale di Fisica Nucleare
Frascati, Latium, Italy
