Publications (67)298.46 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: We describe directed searches for continuous gravitational waves (GWs) in data from the sixth Laser Interferometer Gravitationalwave Observatory (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 10. 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 5.3–25.3 days using the matchedfiltering Fstatistic. We found no evidence of GW signals. We set 95% confidence upper limits as strong (low) as 4 × 10^(−25) on intrinsic strain, 2 × 10^(−7) on fiducial ellipticity, and 4 × 10^(−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: 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. 
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. 
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 results of a search for continuously emitted gravitational radiation, directed at the brightest lowmass xray binary, Scorpius X1. Our semicoherent analysis covers 10 days of LIGO S5 data ranging from 50–550 Hz, and performs an incoherent sum of coherent Fstatistic 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 1.3×10^(−24) and 8×10^(−25) are reported at 150 Hz for the standard and anglerestricted searches respectively. This proofofprinciple 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: 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 gravitationalwave 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 assuming both that 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 2 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: 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: 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 the LIGO and Virgo detectors. Consistent with predictions from most stochastic gravitationalwave background models, the data display no evidence of a stochastic gravitationalwave signal. Assuming a gravitationalwave spectrum of Ω_(GW)(f)=Ω_α(f/f_(ref))_α, we place 95% confidence level upper limits on the energy density of the background in each of four frequency bands spanning 41.5–1726 Hz. In the frequency band of 41.5–169.25 Hz for a spectral index of α=0, we constrain the energy density of the stochastic background to be Ω_(GW)(f)<5.6×10^(−6). For the 600–1000 Hz band, Ω_(GW)(f)<0.14(f/900 Hz)^3, a factor of 2.5 lower than the best previously reported upper limits. We find Ω_(GW)(f)<1.8×10^(−4) using a spectral index of zero for 170–600 Hz and Ω_(GW)(f)<1.0(f/1300 Hz)^3 for 1000–1726 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 possible evidence for inflationary gravitational waves.  [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: 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 2007–2010. These include parts of the 2005–2007 run and the 2009–2010 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_⊙c^2 at ∼150 Hz with ∼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 1.6×10^(−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: 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. 
Article: First allsky search for continuous gravitational waves from unknown sources in binary systems
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ABSTRACT: We present the first results of an allsky search for continuous gravitational waves from unknown spinning neutron stars in binary systems using LIGO and Virgo data. Using a specially developed analysis program, the TwoSpect algorithm, the search was carried out on data from the sixth LIGO science run and the second and third Virgo science runs. The search covers a range of frequencies from 20 Hz to 520 Hz, a range of orbital periods from 2 to ∼2,254 h and a frequency and perioddependent range of frequency modulation depths from 0.277 to 100 mHz. This corresponds to a range of projected semimajor axes of the orbit from ∼0.6×10^(−3) ls to ∼6,500 ls assuming the orbit of the binary is circular. While no plausible candidate gravitational wave events survive the pipeline, upper limits are set on the analyzed data. The most sensitive 95% confidence upper limit obtained on gravitational wave strain is 2.3×10^(−24) at 217 Hz, assuming the source waves are circularly polarized. Although this search has been optimized for circular binary orbits, the upper limits obtained remain valid for orbital eccentricities as large as 0.9. In addition, upper limits are placed on continuous gravitational wave emission from the lowmass xray binary Scorpius X1 between 20 Hz and 57.25 Hz.  [Show abstract] [Hide abstract]
ABSTRACT: We present an implementation of the Fstatistic 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 Hz) x 10^(9) Hz s^(−1) 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 Fstatistic, 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 Fstatistic 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 x 10^(24). 
Article: Search for Gravitational Waves Associated with γray Bursts Detected by the Interplanetary Network
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ABSTRACT: We present the results of a search for gravitational waves associated with 223 γray bursts (GRBs) detected by the InterPlanetary Network (IPN) in 2005–2010 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 gravitational wave search sensitivity as compared to corresponding alltime, allsky searches. We find no evidence of a gravitational wave signal associated with any of the IPN GRBs in the sample, nor do we find evidence for a population of weak gravitational wave signals associated with the GRBs. For all IPNdetected GRBs, for which a sufficient duration of quality gravitational wave data are available, we place lower bounds on the distance to the source in accordance with an optimistic assumption of gravitational wave emission energy of 10^(−2)M⊙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 12 Mpc, 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 gravitational wave detectors and a resulting examination of prospects for the advanced gravitational wave detectors. 
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.
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1k  Citations  
298.46  Total Impact Points  
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20112014

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