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Register a new userCalibration of the LIGO Gravitational Wave Detectors in the Fifth Science Run
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The Laser Interferometer Gravitational Wave Observatory (LIGO) is a network of three detectors built to detect local perturbations in the space-time metric from astrophysical sources. These detectors, two in Hanford, WA and one in Livingston, LA, are power-recycled Fabry-Perot Michelson interferometers. In their fifth science run (S5), between November 2005 and October 2007, these detectors accumulated one year of triple coincident data while operating at their designed sensitivity. In this paper, we describe the calibration of the instruments in the S5 data set, including measurement techniques and uncertainty estimation.
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In 2009-2010, the Laser Interferometer Gravitational-wave 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 gravitational-wave 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.
The LIGO Scientific Collaboration (LSC) glitch group is part of the LIGO detector characterization effort. It consists of data analysts and detector experts who, during and after science runs, collaborate for a better understanding of noise transients in the detectors. Goals of the glitch group during the fifth LIGO science run (S5) included (1) offline assessment of the detector data quality, with focus on noise transients, (2) veto recommendations for astrophysical analysis and (3) feedback to the commissioning team on anomalies seen in gravitational wave and auxiliary data channels. Other activities included the study of auto-correlation of triggers from burst searches, stationarity of the detector noise and veto studies. The group identified causes for several noise transients that triggered false alarms in the gravitational wave searches; the times of such transients were identified and vetoed from the data generating the LSC astrophysical results.
We describe the influence of environmental noise on LIGO detectors in the sixth science run (S6), from July 2009 to October 2010. We show results from experimental investigations testing the coupling level and mechanisms for acoustic, electromagnetic/magnetic and seismic noise to the instruments. We argument the sensors importance for vetoes of false positive detections, report estimates of the noise sources contributions to the detector background, and discuss the ways in which environmental coupling should be reduced in the LIGO upgrade, Advanced LIGO.
The sensitivity of gravitational wave searches for binary black holes is estimated via the injection and posterior recovery of simulated gravitational wave signals in the detector data streams. When a search reports no detections, the estimated sensitivity is then used to place upper limits on the coalescence rate of the target source. In order to obtain correct sensitivity and rate estimates, the injected waveforms must be faithful representations of the real signals. Up to date, however, injected waveforms have neglected radiation modes of order higher than the quadrupole, potentially biasing sensitivity and coalescence rate estimates. In particular, higher-order modes are known to have a large impact in the gravitational waves emitted by intermediate mass black holes binaries. In this work we evaluate the impact of this approximation in the context of two search algorithms run by the LIGO Scientific Collaboration in their search for intermediate mass black hole binaries in the O1 LIGO Science Run data: a matched-filter based pipeline and a coherent un-modeled one. To this end we estimate the sensitivity of both searches to simulated signals including and omitting higher-order modes. We find that omission of higher-order modes leads to biases in the sensitivity estimates which depend on the masses of the binary, the search algorithm and the required level of significance for detection. In addition, we compare the sensitivity of the two search algorithms across the studied parameter space. We conclude that the most recent LIGO-Virgo upper limits on the rate of coalescence of intermediate mass black hole binaries are conservative for the case of highly asymmetric binaries. However, the tightest upper limits, placed for nearly-equal-mass sources, remain unchanged due to the small contribution of higher modes to the corresponding sources.
We report on a comprehensive all-sky search for periodic gravitational waves in the frequency band 100-1500 Hz and with a frequency time derivative in the range of $[-1.18, +1.00]times 10^{-8}$ Hz/s. Such a signal could be produced by a nearby spinning and slightly non-axisymmetric isolated neutron star in our galaxy. This search uses the data from the Initial LIGO sixth science run and covers a larger parameter space with respect to any past search. A Loosely Coherent detection pipeline was applied to follow up weak outliers in both Gaussian (95% recovery rate) and non-Gaussian (75% recovery rate) bands. No gravitational wave signals were observed, and upper limits were placed on their strength. Our smallest upper limit on worst-case (linearly polarized) strain amplitude $h_0$ is ${9.7}times 10^{-25}$ near 169 Hz, while at the high end of our frequency range we achieve a worst-case upper limit of ${5.5}times 10^{-24}$. Both cases refer to all sky locations and entire range of frequency derivative values.
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