3,261 research outputs found
Designing a template bank to observe compact binary coalescences in Advanced LIGO's second observing run
We describe the methodology and novel techniques used to construct a set of
waveforms, or template bank, applicable to searches for compact binary
coalescences in Advanced LIGO's second observing run. This template bank is
suitable for observing systems composed of two neutron stars, two black holes,
or a neutron star and a black hole. The Post-Newtonian formulation is used to
model waveforms with total mass less than 4 and the most recent
effective-one-body model, calibrated to numerical relativity to include the
merger and ringdown, is used for total masses greater than 4 . The
effects of spin precession, matter, orbital eccentricity and radiation modes
beyond the quadrupole are neglected. In contrast to the template bank used to
search for compact binary mergers in Advanced LIGO's first observing run, here
we are including binary-black-hole systems with total mass up to several
hundreds of solar masses, thereby improving the ability to observe such
systems. We introduce a technique to vary the starting frequency of waveform
filters so that our bank can simultaneously contain binary-neutron-star and
high-mass binary-black hole waveforms. We also introduce a lower-bound on the
filter waveform length, to exclude very short-duration, high-mass templates
whose sensitivity is strongly reduced by the characteristics and performance of
the interferometers.Comment: 10 pages, 8 figure
ISSUES IN THE ADMINISTRATION OF TARIFF-RATE IMPORT QUOTAS IN THE AGREEMENT ON AGRICULTURE IN THE WTO: AN INTRODUCTION
International Relations/Trade,
Numerical Relativity Injection Infrastructure
This document describes the new Numerical Relativity (NR) injection
infrastructure in the LIGO Algorithms Library (LAL), which henceforth allows
for the usage of NR waveforms as a discrete waveform approximant in LAL. With
this new interface, NR waveforms provided in the described format can directly
be used as simulated GW signals ("injections") for data analyses, which include
parameter estimation, searches, hardware injections etc. As opposed to the
previous infrastructure, this new interface natively handles sub-dominant modes
and waveforms from numerical simulations of precessing binary black holes,
making them directly accessible to LIGO analyses. To correctly handle
precessing simulations, the new NR injection infrastructure internally
transforms the NR data into the coordinate frame convention used in LAL.Comment: 20 pages, 2 figures, technical repor
Rest Frame Optical Spectra of Lyman Break Galaxies: Other Lensing Arcs around MS1512-cB58
We have obtained near-infrared spectra of two images of the galaxy at z=2.72 which is gravitationally lensed by the foreground cluster MS1512+36. The brighter arc, cB58, is an image of only the nucleus and the southern half of the background galaxy, while the fainter image, A2, encompasses the entire background galaxy. Thus the gravitational lensing provides spatial resolution on a smaller scale than is routinely available by other methods.
Our observations indicate no evidence for any systematic rotational velocity gradient across the face of this galaxy. The nucleus and outer regions of the galaxy do not differ in their gas reddening or excitation level, based on the identical Hα/5007 ratios. cB58 (which is more dominated by the nucleus) has relatively stronger continuum emission, perhaps because of a higher ratio of old to young stars, compared to the outer parts of the galaxy.
A second emission line source, denoted as K1, at a slightly lower redshift was serendipitously detected in the slit. It appears to be the gravitationally lensed image of another background galaxy in the same group as cB58
Convolutional neural networks: a magic bullet for gravitational-wave detection?
In the last few years, machine learning techniques, in particular
convolutional neural networks, have been investigated as a method to replace or
complement traditional matched filtering techniques that are used to detect the
gravitational-wave signature of merging black holes. However, to date, these
methods have not yet been successfully applied to the analysis of long
stretches of data recorded by the Advanced LIGO and Virgo gravitational-wave
observatories. In this work, we critically examine the use of convolutional
neural networks as a tool to search for merging black holes. We identify the
strengths and limitations of this approach, highlight some common pitfalls in
translating between machine learning and gravitational-wave astronomy, and
discuss the interdisciplinary challenges. In particular, we explain in detail
why convolutional neural networks alone cannot be used to claim a statistically
significant gravitational-wave detection. However, we demonstrate how they can
still be used to rapidly flag the times of potential signals in the data for a
more detailed follow-up. Our convolutional neural network architecture as well
as the proposed performance metrics are better suited for this task than a
standard binary classifications scheme. A detailed evaluation of our approach
on Advanced LIGO data demonstrates the potential of such systems as trigger
generators. Finally, we sound a note of caution by constructing adversarial
examples, which showcase interesting "failure modes" of our model, where inputs
with no visible resemblance to real gravitational-wave signals are identified
as such by the network with high confidence.Comment: First two authors contributed equally; appeared at Phys. Rev.
Observing and measuring the neutron-star equation-of-state in spinning binary neutron star systems
LIGO and Virgo recently observed the first binary neutron star merger,
demonstrating that gravitational-waves offer the ability to probe how matter
behaves in one of the most extreme environments in the Universe. However, the
gravitational-wave signal emitted by an inspiraling binary neutron star system
is only weakly dependent on the equation of state and extracting this
information is challenging. Previous studies have focused mainly on binary
systems where the neutron stars are spinning slowly and the main imprint of
neutron star matter in the inspiral signal is due to tidal effects. For
binaries with non-negligible neutron-star spin the deformation of the neutron
star due to its own rotation introduces additional variations in the emitted
gravitational-wave signal. Here we explore whether highly spinning binary
neutron-star systems offer a better chance to measure the equation-of-state
than weakly spinning binary-neutron star systems. We focus on the dominant
adiabatic quadrupolar effects and consider three main questions. First, we show
that equation-of-state effects can be significant in the inspiral waveforms,
and that the spin-quadrupole effect dominates for rapidly rotating neutron
stars. Second, we show that variations in the spin-quadrupole phasing are
strongly degenerate with changes in the component masses and spins, and
neglecting these terms has a negligible impact on the number of observations
with second generation observatories. Finally, we explore the bias in the
masses and spins that would be introduced by using incorrect equation-of-state
terms. Using a novel method to rapidly evaluate an approximation of the
likelihood we show that assuming the incorrect equation-of-state when measuring
source parameters can lead to a significant bias. We also find that the ability
to measure the equation-of-state is improved when considering spinning systems.Comment: 29 pages (CQG formatting), 9 figure
Groups 5 and 6 Terminal Hydrazido(2−) Complexes: N_β Substituent Effects on Ligand-to-Metal Charge-Transfer Energies and Oxidation States
Brightly colored terminal hydrazido(2−) (dme)MCl_3(NNR_2) (dme = 1,2-dimethoxyethane; M = Nb, Ta; R = alkyl, aryl) or (MeCN)WCl_4(NNR_2) complexes have been synthesized and characterized. Perturbing the electronic environment of the β (NR_2) nitrogen affects the energy of the lowest-energy charge-transfer (CT) transition in these complexes. For group 5 complexes, increasing the energy of the N_β lone pair decreases the ligand-to-metal CT (LMCT) energy, except for electron-rich niobium dialkylhydrazides, which pyramidalize N_β in order to reduce the overlap between the Nb═Nα π bond and the Nβ lone pair. For W complexes, increasing the energy of N_β eventually leads to reduction from formally [W^(VI)≡N–NR_2] with a hydrazido(2−) ligand to [W^(IV)═N═NR_2] with a neutral 1,1-diazene ligand. The photophysical properties of these complexes highlight the potential redox noninnocence of hydrazido ligands, which could lead to ligand- and/or metal-based redox chemistry in early transition metal derivatives
When can gravitational-wave observations distinguish between black holes and neutron stars?
Gravitational-wave observations of compact binaries have the potential to
uncover the distribution of masses and angular momenta of black holes and
neutron stars in the universe. The binary components' physical parameters can
be inferred from their effect on the phasing of the gravitational-wave signal,
but a partial degeneracy between the components' mass ratio and their angular
momenta limits our ability to measure the individual component masses. At the
typical signal amplitudes expected by the Advanced Laser Interferometer
Gravitational-wave Observatory (signal-to-noise ratios between 10 and 20), we
show that it will in many cases be difficult to distinguish whether the
components are neutron stars or black holes. We identify when the masses of the
binary components could be unambiguously measured outside the range of current
observations: a system with a chirp mass M
would unambiguously contain the smallest-mass neutron star observed, and a
system with \mathcal{M} \ge 2.786 \Msun must contain a black hole. However,
additional information would be needed to distinguish between a binary
containing two 1.35 M neutron stars and an exotic
neutron-star--black-hole binary. We also identify those configurations that
could be unambiguously identified as black-hole binaries, and show how the
observation of an electromagnetic counterpart to a neutron-star--black-hole
binary could be used to constrain the black-hole spin.Comment: 5 pages, 4 figures. Final version to be published in Ap.J.Let
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