133 research outputs found
Search for Tensor, Vector, and Scalar Polarizations in the Stochastic Gravitational-Wave Background
The detection of gravitational waves with Advanced LIGO and Advanced Virgo has enabled novel tests of general relativity, including direct study of the polarization of gravitational waves. While general relativity allows for only two tensor gravitational-wave polarizations, general metric theories can additionally predict two vector and two scalar polarizations. The polarization of gravitational waves is encoded in the spectral shape of the stochastic gravitational-wave background, formed by the superposition of cosmological and individually unresolved astrophysical sources. Using data recorded by Advanced LIGO during its first observing run, we search for a stochastic background of generically polarized gravitational waves. We find no evidence for a background of any polarization, and place the first direct bounds on the contributions of vector and scalar polarizations to the stochastic background. Under log-uniform priors for the energy in each polarization, we limit the energy densities of tensor, vector, and scalar modes at 95% credibility to Ω0T<5.58×10-8, Ω0V<6.35×10-8, and Ω0S<1.08×10-7 at a reference frequency f0=25 Hz. © 2018 American Physical Society
All-sky search for long-duration gravitational wave transients with initial LIGO
We present the results of a search for long-duration 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 s 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 long-duration gravitational wave transients for different types of gravitational wave signals. For signals from black hole accretion disk instabilities, we set upper limits on the source rate density between 3.4×10-5 and 9.4×10-4 Mpc-3 yr-1 at 90% confidence. These are the first results from an all-sky search for unmodeled long-duration transient gravitational waves. © 2016 American Physical Society
All-sky search for long-duration gravitational wave transients with initial LIGO
We present the results of a search for long-duration 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 s 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 long-duration gravitational wave transients for different types of gravitational wave signals. For signals from black hole accretion disk instabilities, we set upper limits on the source rate density between 3.4×10-5 and 9.4×10-4 Mpc-3 yr-1 at 90% confidence. These are the first results from an all-sky search for unmodeled long-duration transient gravitational waves. © 2016 American Physical Society
On the progenitor of binary neutron star merger GW170817
On 2017 August 17 the merger of two compact objects with masses consistent with two neutron stars was discovered through gravitational-wave (GW170817), gamma-ray (GRB 170817A), and optical (SSS17a/AT 2017gfo) observations. The optical source was associated with the early-type galaxy NGC 4993 at a distance of just ∼40 Mpc, consistent with the gravitational-wave measurement, and the merger was localized to be at a projected distance of ∼2 kpc away from the galaxy's center. We use this minimal set of facts and the mass posteriors of the two neutron stars to derive the first constraints on the progenitor of GW170817 at the time of the second supernova (SN). We generate simulated progenitor populations and follow the three-dimensional kinematic evolution from binary neutron star (BNS) birth to the merger time, accounting for pre-SN galactic motion, for considerably different input distributions of the progenitor mass, pre-SN semimajor axis, and SN-kick velocity. Though not considerably tight, we find these constraints to be comparable to those for Galactic BNS progenitors. The derived constraints are very strongly influenced by the requirement of keeping the binary bound after the second SN and having the merger occur relatively close to the center of the galaxy. These constraints are insensitive to the galaxy's star formation history, provided the stellar populations are older than 1 Gyr
Constraints on cosmic strings using data from the first Advanced LIGO observing run
Cosmic strings are topological defects which can be formed in grand unified theory scale phase transitions in the early universe. They are also predicted to form in the context of string theory. The main mechanism for a network of Nambu-Goto cosmic strings to lose energy is through the production of loops and the subsequent emission of gravitational waves, thus offering an experimental signature for the existence of cosmic strings. Here we report on the analysis conducted to specifically search for gravitational-wave bursts from cosmic string loops in the data of Advanced LIGO 2015-2016 observing run (O1). No evidence of such signals was found in the data, and as a result we set upper limits on the cosmic string parameters for three recent loop distribution models. In this paper, we initially derive constraints on the string tension Gμ and the intercommutation probability, using not only the burst analysis performed on the O1 data set but also results from the previously published LIGO stochastic O1 analysis, pulsar timing arrays, cosmic microwave background and big-bang nucleosynthesis experiments. We show that these data sets are complementary in that they probe gravitational waves produced by cosmic string loops during very different epochs. Finally, we show that the data sets exclude large parts of the parameter space of the three loop distribution models we consider
Archaeology among the bird droppings: what does it tell us about raptor nest-site selection?
Some fascinating questions are raised by Kurt and William Burnham and Ian Newton's findings, reported in this issue of Ibis, that 14C dating has shown some Gyrfalcon Falco rusticolus nests to have been occupied for around the past 2500 years. As the authors demonstrate, this finding could make an important contribution to our understanding of climate change in the high arctic. And stable isotope analysis also has the potential to record changes in prey selection and foraging habitat over long periods of time. Other detritus from nest-sites can also achieve this
Amino acid composition of some woodland arthropods and its implications for breeding tits and other passerines
Breeding of the lappet-faced and white-headed vultures (Torgos tracheliotus Forster and Trigonoceps occipitalis Burchell) on the Serengeti Plains, Tanzania
Metabarcoding avian diets at airports: implications for birdstrike hazard management planning
Background: Wildlife collisions with aircraft cost the airline industry billions ofdollars per annum and represent a public safety risk. Clearly, adaptingaerodrome habitats to become less attractive to hazardous wildlife willreduce the incidence of collisions. Formulating effective habitat managementstrategies relies on accurate species identification of high-risk species.This can be successfully achieved for all strikes either through morphologyand/or DNA-based identifications. Beyond species identification, dietaryanalysis of birdstrike gut contents can provide valuable intelligence forairport hazard management practices in regards to what food is attractingwhich species to aerodromes. Here, we present birdstrike identification anddietary data from Perth Airport, Western Australia, an aerodrome that sawapproximately 140,000 aircraft movements in 2012. Next-generation highthroughput DNA sequencing was employed to investigate 77 carcasses from 16bird species collected over a 12-month period. Five DNA markers, whichbroadly characterize vertebrates, invertebrates and plants, were used totarget three animal mitochondrial genes (12S rRNA, 16S rRNA, and COI) and aplastid gene (trnL) from DNA extracted from birdstrike carcassgastrointestinal tracts.Results: Over 151,000 DNA sequences were generated, filtered and analyzed by afusion-tag amplicon sequencing approach. Across the 77 carcasses, the mostcommonly identified vertebrate was Mus musculus (house mouse).Acrididae (grasshoppers) was the most common invertebrate family identified,and Poaceae (grasses) the most commonly identified plant family. TheDNA-based dietary data has the potential to provide some key insights intofeeding ecologies within and around the aerodrome.Conclusions: The data generated here, together with the methodological approach, willgreatly assist in the development of hazard management plans and, incombination with existing observational studies, provide an improved way tomonitor the effectiveness of mitigation strategies (for example, netting ofwater, grass type, insecticides and so on) at aerodromes. It is hoped thatwith the insights provided by dietary data, airports will be able toallocate financial resources to the areas that will achieve the bestoutcomes for birdstrike reduction
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