Publications (91)352.82 Total impact

 [Show abstract] [Hide abstract]
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.  [Show abstract] [Hide abstract]
ABSTRACT: The GermanBritish laserinterferometric gravitational wave detector GEO 600 is in its 14th year of operation since its first lock in 2001. After GEO 600 participated in science runs with other firstgeneration detectors, a program known as GEOHF began in 2009. The goal was to improve the detector sensitivity at high frequencies with technologically advanced yet minimally invasive upgrades. Simultaneously, the detector would record science quality data in between commissioning activities. As of early 2014, all of the planned upgrades have been carried out and sensitivity improvements of up to a factor of four at the highfrequency end of the observation band have been achieved. Besides science data collection, an experimental program is ongoing with the goal to further improve the sensitivity and evaluate future detector technologies. We summarize the results of the GEOHF program to date and discuss its successes and challenges.  [Show abstract] [Hide abstract]
ABSTRACT: Beam alignment is an important practical aspect of the application of squeezed states of light. Misalignments in the detection of squeezed light result in a reduction of the observable squeezing level. In the case of squeezed vacuum fields that contain only very few photons, special measures must be taken in order to sense and control the alignment of the essentially dark beam. The GEO600 gravitational wave detector employs a squeezed vacuum source to improve its detection sensitivity beyond the limits set by classical quantum shot noise. Here, we present our design and implementation of an alignment sensing and control scheme that ensures continuous optimal alignment of the squeezed vacuum field at GEO 600 on long time scales in the presence of freeswinging optics. This first demonstration of a squeezed light automatic alignment system will be of particular interest for future longterm applications of squeezed vacuum states of light. 
Article: Advanced LIGO
[Show abstract] [Hide abstract]
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: Gravitational wave interferometers are complex instruments, requiring years of commissioning to achieve the required sensitivities for the detection of gravitational waves, of order 10^21 in dimensionless detector strain, in the tens of Hz to several kHz frequency band. Investigations carried out by the GEO600 detector characterisation group have shown that detector characterisation techniques are useful when planning for commissioning work. At the time of writing, GEO600 is the only large scale laser interferometer currently in operation running with a high duty factor, 70%, limited chiefly by the time spent commissioning the detector. The number of observable gravitational wave sources scales as the product of the volume of space to which the detector is sensitive and the observation time, so the goal of commissioning is to improve the detector sensitivity with the least possible detector down time. We demonstrate a method for increasing the number of sources observable by such a detector, by assessing the severity of nonastrophysical noise contaminations to efficiently guide commissioning. This method will be particularly useful in the early stages and during the initial science runs of the aLIGO and adVirgo detectors, as they are brought up to design performance.  [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: Quantum noise will be the dominant noise source for the advanced laser interferometric gravitational wave detectors currently under construction. Squeezingenhanced laser interferometers have been recently demonstrated as a viable technique to reduce quantum noise. We propose two new methods of generating an error signal for matching the longitudinal phase of squeezed vacuum states of light to the phase of the laser interferometer output field. Both provide a superior signal to the one used in previous demonstrations of squeezing applied to a gravitationalwave detector. We demonstrate that the new signals are less sensitive to misalignments and higher order modes, and result in an improved stability of the squeezing level. The new signals also offer the potential of reducing the overall rms phase noise and optical losses, each of which would contribute to achieving a higher level of squeezing. The new error signals are a pivotal development towards realizing the goal of 6 dB and more of squeezing in advanced detectors and beyond. 
Article: Advanced techniques in GEO 600
[Show abstract] [Hide abstract]
ABSTRACT: For almost 20 years, advanced techniques have been developed and tested at the GEO 600 laserinterferometric gravitational wave detector. Many of these innovations have improved the sensitivity of GEO 600 and could be shown to be consistent with stable and reliable operation of gravitational wave detectors. We review the performance of these techniques and show how they have influenced the upgrades of other detectors worldwide. In the second half of the paper, we consider how GEO 600 continues to pioneer new techniques for future gravitational wave detectors. We describe some of the new methods in detail and present new results on how they improve the sensitivity and/or the stability of GEO 600 and possibly of future detectors.  [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: Search for Gravitational Waves Associated with γ ray Bursts Detected by the Interplanetary Network
[Show abstract] [Hide abstract]
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. 
Article: First allsky search for continuous gravitational waves from unknown sources in binary systems
[Show abstract] [Hide abstract]
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 ~0.6e3 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 2.3e24 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: In this paper we report on a search for shortduration gravitational wave bursts in the frequency range 64 Hz1792 Hz associated with gammaray bursts (GRBs), using data from GEO600 and one of the LIGO or Virgo detectors. We introduce the method of a linear search grid to analyse GRB events with large sky localisation uncertainties such as the localisations provided by the Fermi Gammaray Burst Monitor (GBM). Coherent searches for gravitational waves (GWs) can be computationally intensive when the GRB sky position is not welllocalised, due to the corrections required for the difference in arrival time between detectors. Using a linear search grid we are able to reduce the computational cost of the analysis by a factor of O(10) for GBM events. Furthermore, we demonstrate that our analysis pipeline can improve upon the sky localisation of GRBs detected by the GBM, if a highfrequency GW signal is observed in coincidence. We use the linear search grid method in a search for GWs associated with 129 GRBs observed satellitebased gammaray experiments between 2006 and 2011. The GRBs in our sample had not been previously analysed for GW counterparts. A fraction of our GRB events are analysed using data from GEO600 while the detector was using squeezedlight states to improve its sensitivity; this is the first search for GWs using data from a squeezedlight interferometric observatory. We find no evidence for GW signals, either with any individual GRB in this sample or with the population as a whole. For each GRB we place lower bounds on the distance to the progenitor, assuming a fixed GW emission energy of $10^{2} M_{\odot}c^{2}$, with a median exclusion distance of 0.8 Mpc for emission at 500 Hz and 0.3 Mpc at 1 kHz. The reduced computational cost associated with a linear search grid will enable rapid searches for GWs associated with Fermi GBM events in the Advanced detector era.
Publication Stats
1k  Citations  
352.82  Total Impact Points  
Top Journals
Institutions

20132015

Max Planck Institute for Physics
München, Bavaria, Germany


20102015

Leibniz Universität Hannover
 Institute of Gravitation Physics
Hanover, Lower Saxony, Germany 
University of Glasgow
 School of Physics and Astronomy
Glasgow, Scotland, United Kingdom


20122014

Max Planck Institute for Gravitational Physics (AlbertEinsteinInstitute)
Potsdam, Brandenburg, Germany
