Publications (32)106.59 Total impact
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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.03/2014;  [show abstract] [hide abstract]
ABSTRACT: We report results from a search for gravitational waves produced by perturbed intermediate mass black holes (IMBH) in data collected by LIGO and Virgo between 2005 and 2010. The search was sensitive to astrophysical sources that produced damped sinusoid gravitational wave signals, also known as ringdowns, with frequency $50\le f_{0}/\mathrm{Hz} \le 2000$ and decay timescale $0.0001\lesssim \tau/\mathrm{s} \lesssim 0.1$ characteristic of those produced in mergers of IMBH pairs. No significant gravitational wave candidate was detected. We report upper limits on the astrophysical coalescence rates of IMBHs with total binary mass $50 \le M/\mathrm{M}_\odot \le 450$ and component mass ratios of either 1:1 or 4:1. For systems with total mass $100 \le M/\mathrm{M}_\odot \le 150$, we report a 90%confidence upper limit on the rate of binary IMBH mergers with nonspinning and equal mass components of $6.9\times10^{8}\,$Mpc$^{3}$yr$^{1}$. We also report a rate upper limit for ringdown waveforms from perturbed IMBHs, radiating 1% of their mass as gravitational waves in the fundamental, $\ell=m=2$, oscillation mode, that is nearly three orders of magnitude more stringent than previous results.03/2014;  [show abstract] [hide abstract]
ABSTRACT: We present an implementation of the $\mathcal{F}$statistic to carry out the first search in data from the Virgo laser interferometric gravitational wave detector for periodic gravitational waves from a priori unknown, isolated rotating neutron stars. We searched a frequency $f_0$ range from 100 Hz to 1 kHz and the frequency dependent spindown $f_1$ range from $1.6\,(f_0/100\,{\rm Hz}) \times 10^{9}\,$ Hz/s to zero. A large part of this frequency  spindown space was unexplored by any of the allsky searches published so far. Our method consisted of a coherent search over twoday periods using the $\mathcal{F}$statistic, followed by a search for coincidences among the candidates from the twoday segments. We have introduced a number of novel techniques and algorithms that allow the use of the Fast Fourier Transform (FFT) algorithm in the coherent part of the search resulting in a fiftyfold speedup in computation of the $\mathcal{F}$statistic with respect to the algorithm used in the other pipelines. No significant gravitational wave signal was found. The sensitivity of the search was estimated by injecting signals into the data. In the most sensitive parts of the detector band more than 90% of signals would have been detected with dimensionless gravitationalwave amplitude greater than $5 \times 10^{24}$.02/2014;  [show abstract] [hide abstract]
ABSTRACT: During the LIGO and Virgo joint science runs in 20092010, gravitational wave (GW) data from three interferometer detectors were analyzed within minutes to select GW candidate events and infer their apparent sky positions. Target coordinates were transmitted to several telescopes for followup observations aimed at the detection of an associated optical transient. Images were obtained for eight such GW candidates. We present the methods used to analyze the image data as well as the transient search results. No optical transient was identified with a convincing association with any of these candidates, and none of the GW triggers showed strong evidence for being astrophysical in nature. We compare the sensitivities of these observations to several model light curves from possible sources of interest, and discuss prospects for future joint GWoptical observations of this type.The Astrophysical Journal Supplement Series 02/2014; 211(1):25. · 16.24 Impact Factor  [show abstract] [hide abstract]
ABSTRACT: The Numerical INJection Analysis (NINJA) project is a collaborative effort between members of the numerical relativity and gravitationalwave astrophysics communities. The purpose of NINJA is to study the ability to detect gravitational waves emitted from merging binary black holes and recover their parameters with nextgeneration gravitationalwave observatories. We report here on the results of the second NINJA project, NINJA2, which employs 60 complete binary black hole hybrid waveforms consisting of a numerical portion modelling the late inspiral, merger, and ringdown stitched to a postNewtonian portion modelling the early inspiral. In a "blind injection challenge" similar to that conducted in recent LIGO and Virgo science runs, we added 7 hybrid waveforms to two months of data recolored to predictions of Advanced LIGO and Advanced Virgo sensitivity curves during their first observing runs. The resulting data was analyzed by gravitationalwave detection algorithms and 6 of the waveforms were recovered with false alarm rates smaller than 1 in a thousand years. Parameter estimation algorithms were run on each of these waveforms to explore the ability to constrain the masses, component angular momenta and sky position of these waveforms. We also perform a largescale montecarlo study to assess the ability to recover each of the 60 hybrid waveforms with early Advanced LIGO and Advanced Virgo sensitivity curves. Our results predict that early Advanced LIGO and Advanced Virgo will have a volumeweighted average sensitive distance of 300Mpc (1Gpc) for $10M_{\odot}+10M_{\odot}$ ($50M_{\odot}+50M_{\odot}$) binary black hole coalescences. We demonstrate that neglecting the component angular momenta in the waveform models used in matchedfiltering will result in a reduction in sensitivity for systems with large component angular momenta. [Abstract abridged for ArXiv, full version in PDF]01/2014;  [show abstract] [hide abstract]
ABSTRACT: Cosmic string cusps produce powerful bursts of gravitational waves (GWs). These bursts provide the most promising observational signature of cosmic strings. In this letter we report stringent limits on cosmic string models obtained from the analysis of 625 days of observation with the LIGO and Virgo GW detectors. A significant fraction of the cosmic string parameter space is ruled out. This result complements and improves existing limits from searches for a stochastic background of GWs using cosmic microwave background and pulsar timing data. In particular, if the size of loops is given by gravitational backreaction, we place upper limits on the string tension $G\mu$ below $10^{8}$ in some regions of the cosmic string parameter space.Physical Review Letters 10/2013; · 7.94 Impact Factor 
Article: A search for longlived gravitationalwave transients coincident with long gammaray bursts
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ABSTRACT: Long gammaray bursts (GRBs) have been linked to extreme corecollapse supernovae from massive stars. Gravitational waves (GW) offer a probe of the physics behind long GRBs. We investigate models of longlived (~101000s) GW emission associated with the accretion disk of a collapsed star or with its protoneutron star remnant. Using data from LIGO's fifth science run, and GRB triggers from the swift experiment, we perform a search for unmodeled longlived GW transients. Finding no evidence of GW emission, we place 90% confidence level upper limits on the GW fluence at Earth from long GRBs for three waveforms inspired by a model of GWs from accretion disk instabilities. These limits range from F<3.5 ergs cm^2 to $F<1200 ergs cm^2, depending on the GRB and on the model, allowing us to probe optimistic scenarios of GW production out to distances as far as ~33 Mpc. Advanced detectors are expected to achieve strain sensitivities 10x better than initial LIGO, potentially allowing us to probe the engines of the nearest long GRBs.Physical Review D 09/2013; 88:122004. · 4.69 Impact Factor  [show abstract] [hide abstract]
ABSTRACT: We present the results of a directed search for continuous gravitational waves from unknown, isolated neutron stars in the Galactic Center region, performed on two years of data from LIGO's fifth science run from two LIGO detectors. The search uses a semicoherent approach, analyzing coherently 630 segments, each spanning 11.5 hours, and then incoherently combining the results of the single segments. It covers gravitational wave frequencies in a range from 78 to 496 Hz and a frequencydependent range of first order spindown values down to 7.86 x 10^8 Hz/s at the highest frequency. No gravitational waves were detected. We place 90% confidence upper limits on the gravitational wave amplitude of sources at the Galactic Center. Placing 90% confidence upper limits on the gravitational wave amplitude of sources at the Galactic Center, we reach ~3.35x10^25 for frequencies near 150 Hz. These upper limits are the most constraining to date for a largeparameterspace search for continuous gravitational wave signals.Physical Review D 09/2013; · 4.69 Impact Factor  [show abstract] [hide abstract]
ABSTRACT: We present the results of searches for gravitational waves from a large selection of pulsars using data from the most recent science runs (S6, VSR2 and VSR4) of the initial generation of interferometric gravitational wave detectors LIGO (Laser Interferometric Gravitationalwave Observatory) and Virgo. We do not see evidence for gravitational wave emission from any of the targeted sources but produce upper limits on the emission amplitude. We highlight the results from seven young pulsars with large spindown luminosities. We reach within a factor of five of the canonical spindown limit for all seven of these, whilst for the Crab and Vela pulsars we further surpass their spindown limits. We present new or updated limits for 172 other pulsars (including both young and millisecond pulsars). Now that the detectors are undergoing major upgrades, and, for completeness, we bring together all of the most uptodate results from all pulsars searched for during the operations of the firstgeneration LIGO, Virgo and GEO600 detectors. This gives a total of 195 pulsars including the most recent results described in this paper.The Astrophysical Journal 09/2013; 785(2):18. · 6.73 Impact Factor 
Article: Enhanced sensitivity of the LIGO gravitational wave detector by using squeezed states of light
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ABSTRACT: Nearly a century after Einstein first predicted the existence of gravitational waves, a global network of Earthbased gravitational wave observatories1, 2, 3, 4 is seeking to directly detect this faint radiation using precision laser interferometry. Photon shot noise, due to the quantum nature of light, imposes a fundamental limit on the attometrelevel sensitivity of the kilometrescale Michelson interferometers deployed for this task. Here, we inject squeezed states to improve the performance of one of the detectors of the Laser Interferometer GravitationalWave Observatory (LIGO) beyond the quantum noise limit, most notably in the frequency region down to 150 Hz, critically important for several astrophysical sources, with no deterioration of performance observed at any frequency. With the injection of squeezed states, this LIGO detector demonstrated the best broadband sensitivity to gravitational waves ever achieved, with important implications for observing the gravitationalwave Universe with unprecedented sensitivity.Nature Photonics 07/2013; 7:613. · 27.25 Impact Factor  [show abstract] [hide abstract]
ABSTRACT: Compact binary systems with neutron stars or black holes are one of the most promising sources for groundbased gravitational wave detectors. Gravitational radiation encodes rich information about source physics; thus parameter estimation and model selection are crucial analysis steps for any detection candidate events. Detailed models of the anticipated waveforms enable inference on several parameters, such as component masses, spins, sky location and distance that are essential for new astrophysical studies of these sources. However, accurate measurements of these parameters and discrimination of models describing the underlying physics are complicated by artifacts in the data, uncertainties in the waveform models and in the calibration of the detectors. Here we report such measurements on a selection of simulated signals added either in hardware or software to the data collected by the two LIGO instruments and the Virgo detector during their most recent joint science run, including a "blind injection" where the signal was not initially revealed to the collaboration. We exemplify the ability to extract information about the source physics on signals that cover the neutron star and black hole parameter space over the individual mass range 1 Msun  25 Msun and the full range of spin parameters. The cases reported in this study provide a snapshot of the status of parameter estimation in preparation for the operation of advanced detectors.04/2013;  [show abstract] [hide abstract]
ABSTRACT: We present a possible observing scenario for the Advanced LIGO and Advanced Virgo gravitational wave detectors over the next decade, with the intention of providing information to the astronomy community to facilitate planning for multimessenger astronomy with gravitational waves. We determine the expected sensitivity of the network to transient gravitationalwave signals, and study the capability of the network to determine the sky location of the source. For concreteness, we focus primarily on gravitationalwave signals from the inspiral of binary neutron star (BNS) systems, as the source considered likely to be the most common for detection and also promising for multimessenger astronomy. We find that confident detections will likely require at least 2 detectors operating with BNS sensitive ranges of at least 100 Mpc, while ranges approaching 200 Mpc should give at least ~1 BNS detection per year even under pessimistic predictions of signal rates. The ability to localize the source of the detected signals depends on the geographical distribution of the detectors and their relative sensitivity, and can be as large as thousands of square degrees with only 2 sensitive detectors operating. Determining the sky position of a significant fraction of detected signals to areas of 5 sq deg to 20 sq deg will require at least 3 detectors of sensitivity within a factor of ~2 of each other and with a broad frequency bandwidth. Should one of the LIGO detectors be relocated in India as expected, many gravitationalwave signals will be localized to a few square degrees by gravitationalwave observations alone.  [show abstract] [hide abstract]
ABSTRACT: The coalescence of a stellarmass compact object into an intermediatemass black hole (intermediate massratio coalescence; IMRAC) is an important astrophysical source for groundbased gravitationalwave interferometers in the socalled advanced configuration. However, the ability to carry out effective matchedfilter based searches for these systems is limited by the lack of reliable waveforms. Here we consider binaries in which the intermediatemass black hole has mass in the range 24  200 solar masses with a stellarmass companion having masses in the range 1.4  18.5 solar masses. In addition, we constrain the mass ratios, q, of the binaries to be in the range 1/140 < q < 1/10 and we restrict our study to the case of circular binaries with nonspinning components. We investigate the relative contribution to the signaltonoise ratio (SNR) of the three different phases of the coalescence: inspiral, merger and ringdown. We show that merger and ringdown contribute to a substantial fraction of the total SNR over a large portion of the mass parameter space, although in a limited portion the SNR is dominated by the inspiral phase. We further identify three regions in the IMRAC massspace in which: (i) inspiralonly searches could be performed with losses in detection rates L in the range 10% < L < 27%, (ii) searches based on inspiralonly templates lead to a loss in detection rates in the range 27% < L < 50%$, and (iii) templates that include merger and ringdown are essential to prevent losses in detection rates greater than 50%. We investigate the effectiveness with which the inspiralonly portion of the IMRAC waveform space is covered by comparing several existing waveform families in this regime. Our results reinforce the importance of extensive numerical relativity simulations of IMRACs and the need for further studies of suitable approximation schemes in this mass range.Physical review D: Particles and fields 02/2013; 88(4).  [show abstract] [hide abstract]
ABSTRACT: We present the first multiwavelength followup observations of two candidate gravitationalwave (GW) transient events recorded by LIGO and Virgo in their 20092010 science run. The events were selected with low latency by the network of GW detectors (within less than 10 minutes) and their candidate sky locations were observed by the Swift observatory (within 12 hr). Image transient detection was used to analyze the collected electromagnetic data, which were found to be consistent with background. Offline analysis of the GW data alone has also established that the selected GW events show no evidence of an astrophysical origin; one of them is consistent with background and the other one was a test, part of a 'blind injection challenge'. With this work we demonstrate the feasibility of rapid followups of GW transients and establish the sensitivity improvement joint electromagnetic and GW observations could bring. This is a first step toward an electromagnetic followup program in the regime of routine detections with the advanced GW instruments expected within this decade. In that regime, multiwavelength observations will play a significant role in completing the astrophysical identification of GW sources. We present the methods and results from this first combined analysis and discuss its implications in terms of sensitivity for the present and future instruments.The Astrophysical Journal Supplement Series 12/2012; 203(2). · 16.24 Impact Factor  [show abstract] [hide abstract]
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{sup 2} M {sub Sun} c {sup 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.The Astrophysical Journal 11/2012; 760(1). · 6.73 Impact Factor  [show abstract] [hide abstract]
ABSTRACT: Accurate parameter estimation of gravitational waves from coalescing compact binary sources is a key requirement for gravitationalwave astronomy. Evaluating the posterior probability density function of the binary's parameters (component masses, sky location, distance, etc.) requires computing millions of waveforms. The computational expense of parameter estimation is dominated by waveform generation and scales linearly with the waveform computational cost. Previous work showed that gravitational waveforms from nonspinning compact binary sources are amenable to a truncated singular value decomposition, which allows them to be reconstructed via interpolation at fixed computational cost. However, the accuracy requirement for parameter estimation is typically higher than for searches, so it is crucial to ascertain that interpolation does not lead to significant errors. Here we provide a proof of principle to show that interpolated waveforms can be used to recover posterior probability density functions with negligible loss in accuracy with respect to noninterpolated waveforms. This technique has the potential to significantly increase the efficiency of parameter estimation.Physical review D: Particles and fields 11/2012; 87(12).  [show abstract] [hide abstract]
ABSTRACT: We report a search for gravitational waves from the inspiral, merger and ringdown of binary black holes (BBH) with total mass between 25 and 100 solar masses, in data taken at the LIGO and Virgo observatories between July 7, 2009 and October 20, 2010. The maximum sensitive distance of the detectors over this period for a (20,20) Msun coalescence was 300 Mpc. No gravitational wave signals were found. We thus report upper limits on the astrophysical coalescence rates of BBH as a function of the component masses for nonspinning components, and also evaluate the dependence of the search sensitivity on component spins aligned with the orbital angular momentum. We find an upper limit at 90% confidence on the coalescence rate of BBH with nonspinning components of mass between 19 and 28 Msun of 3.3 \times 10^7 mergers /Mpc^3 /yr.09/2012;  [show abstract] [hide abstract]
ABSTRACT: This paper presents results of an allsky searches for periodic gravitational waves in the frequency range [50, 1190] Hz and with frequency derivative ranges of [2 x 10^9, 1.1 x 10^10] Hz/s for the fifth LIGO science run (S5). The novelty of the search lies in the use of a noncoherent technique based on the Houghtransform to combine the information from coherent searches on timescales of about one day. Because these searches are very computationally intensive, they have been deployed on the Einstein@Home distributed computing project infrastructure. The search presented here is about a factor 3 more sensitive than the previous Einstein@Home search in early S5 LIGO data. The postprocessing has left us with eight surviving candidates. We show that deeper followup studies rule each of them out. Hence, since no statistically significant gravitational wave signals have been detected, we report upper limits on the intrinsic gravitational wave amplitude h0. For example, in the 0.5 Hzwide band at 152.5 Hz, we can exclude the presence of signals with h0 greater than 7.6 x 10^25 with a 90% confidence level.07/2012;  [show abstract] [hide abstract]
ABSTRACT: Pulsar Timing Arrays are a prime tool to study unexplored astrophysical regimes with gravitational waves. Here we show that the detection of gravitational radiation from individually resolvable supermassive black hole binary systems can yield direct information about the masses and spins of the black holes, provided that the gravitationalwave induced timing fluctuations both at the pulsar and at the Earth are detected. This in turn provides a map of the nonlinear dynamics of the gravitational field and a new avenue to tackle open problems in astrophysics connected to the formation and evolution of supermassive black holes. We discuss the potential, the challenges and the limitations of these observations.Physical Review Letters 07/2012; 109(8). · 7.94 Impact Factor  [show abstract] [hide abstract]
ABSTRACT: We present the results of the first search for gravitational wave bursts associated with high energy neutrinos. Together, these messengers could reveal new, hidden sources that are not observed by conventional photon astronomy, particularly at high energy. Our search uses neutrinos detected by the underwater neutrino telescope ANTARES in its 5 line configuration during the period January  September 2007, which coincided with the fifth and first science runs of LIGO and Virgo, respectively. The LIGOVirgo data were analysed for candidate gravitationalwave signals coincident in time and direction with the neutrino events. No significant coincident events were observed. We place limits on the density of joint high energy neutrino  gravitational wave emission events in the local universe, and compare them with densities of merger and corecollapse events.05/2012;
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106.59  Total Impact Points  
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2011–2013

University of Birmingham
 School of Physics and Astronomy
Birmingham, England, United Kingdom
