Search for gravitational waves from Scorpius X-1 in the second Advanced LIGO observing run with an improved hidden Markov model

We present results from a semicoherent search for continuous gravitational waves from the low-mass x-ray binary Scorpius X-1, using a hidden Markov model (HMM) to track spin wandering. This search improves on previous HMM-based searches of LIGO data by using an improved frequency domain matched filter, the J-statistic, and by analyzing data from Advanced LIGO's second observing run. In the frequency range searched, from 60 to 650 Hz, we find no evidence of gravitational radiation. At 194.6 Hz, the most sensitive search frequency, we report an upper limit on gravitational wave strain (at 95% confidence) of h095%=3.47×10-25 when marginalizing over source inclination angle. This is the most sensitive search for Scorpius X-1, to date, that is specifically designed to be robust in the presence of spin wandering. © 2019 American Physical Society

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

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

Introduction of #delta#_5 as an operational definition of the CTOD and its practical use

Reprint from: Standard Technical Publication 1256. Published by American Society for Testing and Materials, West Conshohocken, PA (US)Available from FIZ Karlsruhe / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Recent developments in elastic-plastic fracture mechanics with particular reference to heterogeneous structures

The fracture parameters being used in EPFM are the J-integral and the crack tip opening displacement. Methods are available for determining J and CTOD as driving force parameters as functions of applied load or strain. When using J and CTOD in testing for determining the fracture resistance of a material it is seen that they do not uniquely describe a material's fracture behaviour. This is due to constraint effects which depend on a number of parameters, in particular geometrical parameters. Recently a further source of constraint effects has been extensively reported: if a crack is located near the interface between two mechanically dissimilar materials then the crack tip field may be disturbed, resulting in a variation in the driving force and constraint and hence crack growth resistance. Methods are being developed for determining the driving force and crack growth resistance under these circumstances. (orig.)First published in 'Anales de Mecanica de la fractura, v. 14(1997) p. 30-49' by departamento de Ciencia de Materialse, Universidad Politecnica de Madrid, 30 refs.Available from TIB Hannover: RA 3251(98/E/39) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Welded joints with non-matching weld metal-crack driving force considerations on the basis of the Engineering Treatment Model (ETM)

The application of the Engineering Treatment Model (ETM) to a weld metal crack in a tension loaded transverse welded wide plate yields the applied crack tip opening displacement (CTOD) as a function of applied load or applied strain, if the stress-strain-curves of the base material and the weld metal can be expressed as piece-wise power laws. Simple analytical relationships are obtained which can serve for predicting critical loads, critical strains, or critical crack length. Large effects on the applied CTOD can occur if the weld metal's stress-strain-curve deviates from that of the base material. (orig.)Reprint from: International Journal of Fracture, 62(1993), p. 1-24 / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

A study of the transition from intercrystalline to transcrystalline fatigue crack propagation in different ageing conditions of the alloy Cu-35%Ni-3.5%Cr

The influence of ageing on fatigue fracture of the alloy Cu-35%Ni-3.5%Cr has been investigated. Fatigue cracks propagate in all conditions investigated at first in an intercrystalline and later in a transcrystalline manner. The intercrystalline fraction of the fracture surface increases with increasing cycle number. This is the reason why the improvement of fatigue strength through ageing will be smaller with increasing cycle number, because precipitation hardening can be not fully utilized in the case of pronounced intercrystalline crack propagation. The transition from intercrystalline to transcrystalline crack propagation is determined by a certain stress intensity factor which increases with increasing alternating stress. Because of precipitation hardening, this transition is more difficult in decomposed conditions than in the solution-treated condition. This behaviour is discussed together with the density of microcracks at grain boundaries. (orig.)Reprinted from Int. J. Fatigue (1993) v. 15(1) p. 3-8 / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Crack driving force estimation methods

SIGLEAvailable from TIB Hannover: RA3251(03/32) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman