4,079 research outputs found
Comparison of Gravitational Wave Detector Network Sky Localization Approximations
Gravitational waves emitted during compact binary coalescences are a
promising source for gravitational-wave detector networks. The accuracy with
which the location of the source on the sky can be inferred from gravitational
wave data is a limiting factor for several potential scientific goals of
gravitational-wave astronomy, including multi-messenger observations. Various
methods have been used to estimate the ability of a proposed network to
localize sources. Here we compare two techniques for predicting the uncertainty
of sky localization -- timing triangulation and the Fisher information matrix
approximations -- with Bayesian inference on the full, coherent data set. We
find that timing triangulation alone tends to over-estimate the uncertainty in
sky localization by a median factor of for a set of signals from
non-spinning compact object binaries ranging up to a total mass of , and the over-estimation increases with the mass of the system. We
find that average predictions can be brought to better agreement by the
inclusion of phase consistency information in timing-triangulation techniques.
However, even after corrections, these techniques can yield significantly
different results to the full analysis on specific mock signals. Thus, while
the approximate techniques may be useful in providing rapid, large scale
estimates of network localization capability, the fully coherent Bayesian
analysis gives more robust results for individual signals, particularly in the
presence of detector noise.Comment: 11 pages, 7 Figure
The Effect of the LISA Response Function on Observations of Monochromatic Sources
The Laser Interferometer Space Antenna (LISA) is expected to provide the
largest observational sample of binary systems of faint sub-solar mass compact
objects, in particular white-dwarfs, whose radiation is monochromatic over most
of the LISA observational window. Current astrophysical estimates suggest that
the instrument will be able to resolve about 10000 such systems, with a large
fraction of them at frequencies above 3 mHz, where the wavelength of
gravitational waves becomes comparable to or shorter than the LISA arm-length.
This affects the structure of the so-called LISA transfer function which cannot
be treated as constant in this frequency range: it introduces characteristic
phase and amplitude modulations that depend on the source location in the sky
and the emission frequency. Here we investigate the effect of the LISA transfer
function on detection and parameter estimation for monochromatic sources. For
signal detection we show that filters constructed by approximating the transfer
function as a constant (long wavelength approximation) introduce a negligible
loss of signal-to-noise ratio -- the fitting factor always exceeds 0.97 -- for
f below 10mHz, therefore in a frequency range where one would actually expect
the approximation to fail. For parameter estimation, we conclude that in the
range 3mHz to 30mHz the errors associated with parameter measurements differ
from about 5% up to a factor of 10 (depending on the actual source parameters
and emission frequency) with respect to those computed using the long
wavelength approximation.Comment: replacement version with typos correcte
A How-To for the Mock LISA Data Challenges
The LISA International Science Team Working Group on Data Analysis
(LIST-WG1B) is sponsoring several rounds of mock data challenges, with the
purpose of fostering development of LISA data-analysis capabilities, and of
demonstrating technical readiness for the maximum science exploitation of the
LISA data. The first round of challenge data sets were released at this
Symposium. We describe the models and conventions (for LISA and for
gravitational-wave sources) used to prepare the data sets, the file format used
to encode them, and the tools and resources available to support challenge
participants.Comment: 10 pages, 1 figure, in Proceedings of the Sixth International LISA
Symposium (AIP, 2006
Bayesian coherent analysis of in-spiral gravitational wave signals with a detector network
The present operation of the ground-based network of gravitational-wave laser
interferometers in "enhanced" configuration brings the search for gravitational
waves into a regime where detection is highly plausible. The development of
techniques that allow us to discriminate a signal of astrophysical origin from
instrumental artefacts in the interferometer data and to extract the full range
of information are some of the primary goals of the current work. Here we
report the details of a Bayesian approach to the problem of inference for
gravitational wave observations using a network of instruments, for the
computation of the Bayes factor between two hypotheses and the evaluation of
the marginalised posterior density functions of the unknown model parameters.
The numerical algorithm to tackle the notoriously difficult problem of the
evaluation of large multi-dimensional integrals is based on a technique known
as Nested Sampling, which provides an attractive alternative to more
traditional Markov-chain Monte Carlo (MCMC) methods. We discuss the details of
the implementation of this algorithm and its performance against a Gaussian
model of the background noise, considering the specific case of the signal
produced by the in-spiral of binary systems of black holes and/or neutron
stars, although the method is completely general and can be applied to other
classes of sources. We also demonstrate the utility of this approach by
introducing a new coherence test to distinguish between the presence of a
coherent signal of astrophysical origin in the data of multiple instruments and
the presence of incoherent accidental artefacts, and the effects on the
estimation of the source parameters as a function of the number of instruments
in the network.Comment: 22 page
Constant amplitude and post-overload fatigue crack growth behavior in PM aluminum alloy AA 8009
A recently developed, rapidly solidified, powder metallurgy, dispersion strengthened aluminum alloy, AA 8009, was fatigue tested at room temperature in lab air. Constant amplitude/constant delta kappa and single spike overload conditions were examined. High fatigue crack growth rates and low crack closure levels compared to typical ingot metallurgy aluminum alloys were observed. It was proposed that minimal crack roughness, crack path deflection, and limited slip reversibility, resulting from ultra-fine microstructure, were responsible for the relatively poor da/dN-delta kappa performance of AA 8009 as compared to that of typical IM aluminum alloys
Binary black hole spectroscopy
We study parameter estimation with post-Newtonian (PN) gravitational
waveforms for the quasi-circular, adiabatic inspiral of spinning binary compact
objects. The performance of amplitude-corrected waveforms is compared with that
of the more commonly used restricted waveforms, in Advanced LIGO and EGO. With
restricted waveforms, the properties of the source can only be extracted from
the phasing. For amplitude-corrected waveforms, the spectrum encodes a wealth
of additional information, which leads to dramatic improvements in parameter
estimation. At distances of Mpc, the full PN waveforms allow for
high-accuracy parameter extraction for total mass up to several hundred solar
masses, while with the restricted ones the errors are steep functions of mass,
and accurate parameter estimation is only possible for relatively light stellar
mass binaries. At the low-mass end, the inclusion of amplitude corrections
reduces the error on the time of coalescence by an order of magnitude in
Advanced LIGO and a factor of 5 in EGO compared to the restricted waveforms; at
higher masses these differences are much larger. The individual component
masses, which are very poorly determined with restricted waveforms, become
measurable with high accuracy if amplitude-corrected waveforms are used, with
errors as low as a few percent in Advanced LIGO and a few tenths of a percent
in EGO. The usual spin-orbit parameter is also poorly determined with
restricted waveforms (except for low-mass systems in EGO), but the full
waveforms give errors that are small compared to the largest possible value
consistent with the Kerr bound. This suggests a way of finding out if one or
both of the component objects violate this bound. We also briefly discuss the
effect of amplitude corrections on parameter estimation in Initial LIGO.Comment: 28 pages, many figures. Final version accepted by CQG. More in-depth
treatment of component mass errors and detectability of Kerr bound
violations; improved presentatio
Space-Time Distribution of G-Band and Ca II H-Line Intensity Oscillations in Hinode/SOT-FG Observations
We study the space-time distributions of intensity fluctuations in 2 - 3 hour
sequences of multi-spectral, high-resolution, high-cadence broad-band
filtergram images (BFI) made by the SOT-FG system aboard the Hinode spacecraft.
In the frequency range 5.5 < f < 8.0 mHz both G-band and Ca II H-line
oscillations are suppressed in the presence of magnetic fields, but the
suppression disappears for f > 10 mHz. By looking at G-band frequencies above
10 mHz we find that the oscillatory power, both at these frequencies and at
lower frequencies too, lies in a mesh pattern with cell scale 2 - 3 Mm, clearly
larger than normal granulation, and with correlation times on the order of
hours. The mesh pattern lies in the dark lanes between stable cells found in
time-integrated G-band intensity images. It also underlies part of the bright
pattern in time-integrated H-line emission. This discovery may reflect
dynamical constraints on the sizes of rising granular convection cells together
with the turbulence created in strong intercellular downflows.Comment: 24 pages, 15 figure
Triple Michelson Interferometer for a Third-Generation Gravitational Wave Detector
The upcoming European design study `Einstein gravitational-wave Telescope'
represents the first step towards a substantial, international effort for the
design of a third-generation interferometric gravitational wave detector. It is
generally believed that third-generation instruments might not be installed
into existing infrastructures but will provoke a new search for optimal
detector sites. Consequently, the detector design could be subject to fewer
constraints than the on-going design of the second generation instruments. In
particular, it will be prudent to investigate alternatives to the traditional
L-shaped Michelson interferometer. In this article, we review an old proposal
to use three Michelson interferometers in a triangular configuration. We use
this example of a triple Michelson interferometer to clarify the terminology
and will put this idea into the context of more recent research on
interferometer technologies. Furthermore the benefits of a triangular detector
will be used to motivate this design as a good starting point for a more
detailed research effort towards a third-generation gravitational wave
detector.Comment: Minor corrections to the main text and two additional appendices. 14
pages, 6 figure
- …