Constraints on Cosmic Strings from the LIGO-Virgo Gravitational-Wave Detectors

Cosmic strings can give rise to a large variety of interesting astrophysical phenomena. Among them, powerful bursts of gravitational waves (GWs) produced by cusps are a promising observational signature. In this Letter we present a search for GWs from cosmic string cusps in data collected by the LIGO and Virgo gravitational wave detectors between 2005 and 2010, with over 625 days of live time. We find no evidence of GW signals from cosmic strings. From this result, we derive new constraints on cosmic string parameters, which complement and improve existing limits from previous searches for a stochastic background of GWs from cosmic microwave background measurements and pulsar timing data. In particular, if the size of loops is given by the gravitational backreaction scale, we place upper limits on the string tension Gμ below 10−8 in some regions of the cosmic string parameter space

Search for long-lived gravitational-wave transients coincident with long gamma-ray bursts

Long gamma-ray bursts (GRBs) have been linked to extreme core-collapse supernovae from massive stars. Gravitational waves (GW) offer a probe of the physics behind long GRBs. We investigate models of long-lived (~10–1000 s) 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 long-lived 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 FtoFcm-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

Directed search for continuous gravitational waves from the Galactic center

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 frequency-dependent range of first-order spindown values down to −7.86×10−8  Hz/s at the highest frequency. No gravitational waves were detected. The 90% confidence upper limits on the gravitational wave amplitude of sources at the Galactic center are ∼3.35×10−25 for frequencies near 150 Hz. These upper limits are the most constraining to date for a large-parameter-space search for continuous gravitational wave signals

Application of a Hough search for continuous gravitational waves on data from the fifth LIGO science run

We report on an all-sky search for periodic gravitational waves in the frequency range 50–1000 Hz with the first derivative of frequency in the range −8.9 × 10−10 Hz s−1 to zero in two years of data collected during LIGO\u27s fifth science run. Our results employ a Hough transform technique, introducing a χ2 test and analysis of coincidences between the signal levels in years 1 and 2 of observations that offers a significant improvement in the product of strain sensitivity with compute cycles per data sample compared to previously published searches. Since our search yields no surviving candidates, we present results taking the form of frequency dependent, 95% confidence upper limits on the strain amplitude h0. The most stringent upper limit from year 1 is 1.0 × 10−24 in the 158.00–158.25 Hz band. In year 2, the most stringent upper limit is 8.9 × 10−25 in the 146.50–146.75 Hz band. This improved detection pipeline, which is computationally efficient by at least two orders of magnitude better than our flagship Einstein@Home search, will be important for \u27quick-look\u27 searches in the Advanced LIGO and Virgo detector era

First searches for optical counterparts to gravitational-wave candidate events

During the Laser Interferometer Gravitational-wave Observatory and Virgo joint science runs in 2009-2010, 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 follow-up 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 GW-optical observations of this type

FIRST SEARCHES FOR OPTICAL COUNTERPARTS TO GRAVITATIONAL-WAVE CANDIDATE EVENTS

During the LIGO and Virgo joint science runs in 2009-2010, 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 follow-up 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 GW-optical observations of this type

First joint search for gravitational-wave bursts in LIGO and GEO 600 data

We present the results of the first joint search for gravitational-wave bursts by the LIGO and GEO 600 detectors. We search for bursts with characteristic central frequencies in the band 768–2048 Hz in the data acquired between 22 February and 23 March, 2005 (fourth LSC Science Run–S4). We discuss the inclusion of the GEO 600 data in the Waveburst–CorrPower pipeline that first searches for coincident excess power events without taking into account differences in the antenna responses or strain sensitivities of the various detectors. We compare the performance of this pipeline to that of the coherent Waveburst pipeline based on the maximum likelihood statistic. This likelihood statistic is derived from a coherent sum of the detector data streams that takes into account the antenna patterns and sensitivities of the different detectors in the network. We find that the coherent Waveburst pipeline is sensitive to signals of amplitude 30–50% smaller than the Waveburst–CorrPower pipeline. We perform a search for gravitational-wave bursts using both pipelines and find no detection candidates in the S4 data set when all four instruments were operating stably

Search for long-lived gravitational-wave transients coincident with long gamma-ray bursts

Long gamma-ray bursts (GRBs) have been linked to extreme core-collapse supernovae from massive stars. Gravitational waves (GW) offer a probe of the physics behind long GRBs. We investigate models of long-lived (~10–1000 s) 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 long-lived 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 10× better than initial LIGO, potentially allowing us to probe the engines of the nearest long GRBs.J. Aasi ... D.J. Hosken ... W. Kim ... E.J. King ... J. Munch ... D. J. Ottaway ... P. J. Veitc

Searching for stochastic gravitational waves using data from the two colocated LIGO Hanford detectors

Searches for a stochastic gravitational-wave background (SGWB) using terrestrial detectors typically involve cross-correlating data from pairs of detectors. The sensitivity of such cross-correlation 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 gravitational-wave 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 gravitational-wave signal. However, at high frequencies, 460–1000 Hz, these techniques are sufficient to set a 95% confidence level upper limit on the gravitational-wave energy density of Ω(f) < 7.7 × 10[superscript -4](f/900  Hz)[superscript 3], which improves on the previous upper limit by a factor of ~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.National Science Foundation (U.S.)United States. National Aeronautics and Space AdministrationCarnegie TrustDavid & Lucile Packard FoundationAlfred P. Sloan Foundatio

Phylogenetic patterns are not proxies of community assembly mechanisms (they are far better)

International audience1. The subdiscipline of ‘community phylogenetics’ is rapidly growing and influencing thinking regarding community assembly. In particular, phylogenetic dispersion of co-occurring species within a community is commonly used as a proxy to identify which community assembly processes may have structured a particular community: phylogenetic clustering as a proxy for abiotic assembly, that is habitat filtering, and phylogenetic overdispersion as a proxy for biotic assembly, notably competition.2. We challenge this approach by highlighting (typically) implicit assumptions that are, in reality, only weakly supported, including (i) phylogenetic dispersion reflects trait dispersion; (ii) a given ecological function can be performed only by a single trait state or combination of trait states; (iii)trait similarity causes enhanced competition; (iv) competition causes species exclusion; (v) communities are at equilibrium with processes of assembly having been completed; (vi) assembly through habitat filtering decreases in importance if assembly through competition increases, such that the relative balance of the two can be thus quantified by a single parameter; and (vii) observed phylogenetic dispersion is driven predominantly by local and present-day processes.3. Moreover, technical sophistication of the phylogenetic-patterns-as-proxy approach trades off against sophistication in alternative, potentially more pertinent approaches to directly observe or manipulate assembly processes.4. Despite concerns about using phylogenetic dispersion as a proxy for community assembly processes, we suggest there are underappreciated benefits of quantifying the phylogenetic structure of communities, including (i) understanding how coexistence leads to the macroevolutionary diversification of habitat lineage-pools (i.e. phylogenetic-patterns-as-result approach); and (ii) understanding the macroevolutionary contingency of habitat lineage-pools and how it affects present-day species coexistence in local communities (i.e. phylogeneticpatterns- as-cause approach).5. We conclude that phylogenetic patterns may be little useful as proxy of community assembly. However, such patterns can prove useful to identify and test novel hypotheses on (i) how local coexistence may control macroevolution of the habitat lineage-pool, for example through competition among close relatives triggering displacement and diversification of characters, and (ii) how macroevolution within the habitat lineage-pool may control local coexistence of related species, for example through origin of close relatives that can potentially enter in competition