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

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

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

The effect of social facilitation on foraging success in vultures: a modelling study

The status of many Gyps vulture populations are of acute conservation concern as several show marked and rapid decline. Vultures rely heavily on cues from conspecifics to locate carcasses via local enhancement. A simulation model is developed to explore the roles vulture and carcass densities play in this system, where information transfer plays a key role in locating food. We find a sigmoid relationship describing the probability of vultures finding food as a function of vulture density in the habitat. This relationship suggests a threshold density below which the foraging efficiency of the vulture population will drop rapidly towards zero. Management strategies should closely study this foraging system in order to maintain effective foraging densities