3,726 research outputs found
Separating Gravitational Wave Signals from Instrument Artifacts
Central to the gravitational wave detection problem is the challenge of
separating features in the data produced by astrophysical sources from features
produced by the detector. Matched filtering provides an optimal solution for
Gaussian noise, but in practice, transient noise excursions or ``glitches''
complicate the analysis. Detector diagnostics and coincidence tests can be used
to veto many glitches which may otherwise be misinterpreted as gravitational
wave signals. The glitches that remain can lead to long tails in the matched
filter search statistics and drive up the detection threshold. Here we describe
a Bayesian approach that incorporates a more realistic model for the instrument
noise allowing for fluctuating noise levels that vary independently across
frequency bands, and deterministic ``glitch fitting'' using wavelets as
``glitch templates'', the number of which is determined by a trans-dimensional
Markov chain Monte Carlo algorithm. We demonstrate the method's effectiveness
on simulated data containing low amplitude gravitational wave signals from
inspiraling binary black hole systems, and simulated non-stationary and
non-Gaussian noise comprised of a Gaussian component with the standard
LIGO/Virgo spectrum, and injected glitches of various amplitude, prevalence,
and variety. Glitch fitting allows us to detect significantly weaker signals
than standard techniques.Comment: 21 pages, 18 figure
Transverse Galaxy Velocities from Multiple Topological Images
The study of the kinematics of galaxies within clusters or groups has the
limitation that only one of the three velocity components and only two of the
three spatial components of a galaxy position in six-dimensional phase space
can normally be measured. However, if multiple topological images of a cluster
exist, then the radial positions and sky plane mean velocities of galaxies in
the cluster may also be measurable from photometry of the two cluster images.
The vector arithmetic and principles of the analysis are presented. These are
demonstrated by assuming the suggested topological identification of the
clusters RX J1347.5-1145 and CL 09104+4109 to be correct and deducing the
sky-plane relative velocity component along the axis common to both images of
this would-be single cluster.
Three out of four of the inferred transverse velocities are consistent with
those expected in a rich cluster. A control sample of random `common' sky-plane
axes, independent of the topological hypothesis, implies that this is not
surprising. This shows that while galaxy kinematics are deducible from
knowledge of cosmological topology, it is not easy to use them to refute a
specific candidate manifold.Comment: 13 pages, 7 figures, accepted for MNRA
A radiometer for stochastic gravitational waves
The LIGO Scientific Collaboration recently reported a new upper limit on an
isotropic stochastic background of gravitational waves obtained based on the
data from the 3rd LIGO science Run (S3). Now I present a new method for
obtaining directional upper limits that the LIGO Scientific Collaboration
intends to use for future LIGO science runs and that essentially implements a
gravitational wave radiometer.Comment: 6 pages, 2 figure
Enabling high confidence detections of gravitational-wave bursts
With the advanced LIGO and Virgo detectors taking observations the detection
of gravitational waves is expected within the next few years. Extracting
astrophysical information from gravitational wave detections is a well-posed
problem and thoroughly studied when detailed models for the waveforms are
available. However, one motivation for the field of gravitational wave
astronomy is the potential for new discoveries. Recognizing and characterizing
unanticipated signals requires data analysis techniques which do not depend on
theoretical predictions for the gravitational waveform. Past searches for
short-duration un-modeled gravitational wave signals have been hampered by
transient noise artifacts, or "glitches," in the detectors. In some cases, even
high signal-to-noise simulated astrophysical signals have proven difficult to
distinguish from glitches, so that essentially any plausible signal could be
detected with at most 2-3 level confidence. We have put forth the
BayesWave algorithm to differentiate between generic gravitational wave
transients and glitches, and to provide robust waveform reconstruction and
characterization of the astrophysical signals. Here we study BayesWave's
capabilities for rejecting glitches while assigning high confidence to
detection candidates through analytic approximations to the Bayesian evidence.
Analytic results are tested with numerical experiments by adding simulated
gravitational wave transient signals to LIGO data collected between 2009 and
2010 and found to be in good agreement.Comment: 15 pages, 6 figures, submitted to PR
A test of the Poincare dodecahedral space topology hypothesis with the WMAP CMB data
It has been suggested by Roukema and coworkers (hereafter R04) that the
topology of the Universe as probed by the ``matched circles'' method using the
first year release of the WMAP CMB data, might be that of the Poincar\'e
dodecahedral space (PDS) model. An excess in the correlation of the
``identified circles'' was reported by R04, for circles of angular radius of
~11 deg for a relative phase twist -36deg, hinting that this could be due to a
Clifford translation, if the hypothesized model were true.
R04 did not however specify the statistical significance of the correlation
signal.
We investigate the statistical significance of the signal using Monte Carlo
CMB simulations in a simply connected Universe, and present an updated analysis
using the three-year WMAP data. We find that our analyses of the first and
three year WMAP data provide results that are consistent with the simply
connected space at a confidence level as low as 68%.Comment: 8 pages, 6 figures, typo corrected/replaced to match version
published in A&
Detecting the Cosmic Gravitational Wave Background with the Big Bang Observer
The detection of the Cosmic Microwave Background Radiation (CMB) was one of
the most important cosmological discoveries of the last century. With the
development of interferometric gravitational wave detectors, we may be in a
position to detect the gravitational equivalent of the CMB in this century. The
Cosmic Gravitational Background (CGB) is likely to be isotropic and stochastic,
making it difficult to distinguish from instrument noise. The contribution from
the CGB can be isolated by cross-correlating the signals from two or more
independent detectors. Here we extend previous studies that considered the
cross-correlation of two Michelson channels by calculating the optimal signal
to noise ratio that can be achieved by combining the full set of interferometry
variables that are available with a six link triangular interferometer. In
contrast to the two channel case, we find that the relative orientation of a
pair of coplanar detectors does not affect the signal to noise ratio. We apply
our results to the detector design described in the Big Bang Observer (BBO)
mission concept study and find that BBO could detect a background with
.Comment: 15 pages, 12 Figure
Prospects for observing ultra-compact binaries with space-based gravitational wave interferometers and optical telescopes
Space-based gravitational wave interferometers are sensitive to the galactic
population of ultra-compact binaries. An important subset of the ultra-compact
binary population are those stars that can be individually resolved by both
gravitational wave interferometers and electromagnetic telescopes. The aim of
this paper is to quantify the multi-messenger potential of space-based
interferometers with arm-lengths between 1 and 5 Gm. The Fisher Information
Matrix is used to estimate the number of binaries from a model of the Milky Way
which are localized on the sky by the gravitational wave detector to within 1
and 10 square degrees and bright enough to be detected by a magnitude limited
survey. We find, depending on the choice of GW detector characteristics,
limiting magnitude, and observing strategy, that up to several hundred
gravitational wave sources could be detected in electromagnetic follow-up
observations.Comment: 6 pages, 3 figures Updated to include new results. Submitted to MNRA
Co-accelerated particles in the C-metric
With appropriately chosen parameters, the C-metric represents two uniformly
accelerated black holes moving in the opposite directions on the axis of the
axial symmetry (the z-axis). The acceleration is caused by nodal singularities
located on the z-axis.
In the~present paper, geodesics in the~C-metric are examined. In general
there exist three types of timelike or null geodesics in the C-metric:
geodesics describing particles 1) falling under the black hole horizon;
2)crossing the acceleration horizon; and 3) orbiting around the z-axis and
co-accelerating with the black holes.
Using an effective potential, it can be shown that there exist stable
timelike geodesics of the third type if the product of the parameters of the
C-metric, mA, is smaller than a certain critical value. Null geodesics of the
third type are always unstable. Special timelike and null geodesics of the
third type are also found in an analytical form.Comment: 10 pages, 12 EPS figures, changes mainly in abstract & introductio
Space missions to detect the cosmic gravitational-wave background
It is thought that a stochastic background of gravitational waves was
produced during the formation of the universe. A great deal could be learned by
measuring this Cosmic Gravitational-wave Background (CGB), but detecting the
CGB presents a significant technological challenge. The signal strength is
expected to be extremely weak, and there will be competition from unresolved
astrophysical foregrounds such as white dwarf binaries. Our goal is to identify
the most promising approach to detect the CGB. We study the sensitivities that
can be reached using both individual, and cross-correlated pairs of space based
interferometers. Our main result is a general, coordinate free formalism for
calculating the detector response that applies to arbitrary detector
configurations. We use this general formalism to identify some promising
designs for a GrAvitational Background Interferometer (GABI) mission. Our
conclusion is that detecting the CGB is not out of reach.Comment: 22 pages, 7 figures, IOP style, References Adde
Inferring the post-merger gravitational wave emission from binary neutron star coalescences
We present a robust method to characterize the gravitational wave emission
from the remnant of a neutron star coalescence. Our approach makes only minimal
assumptions about the morphology of the signal and provides a full posterior
probability distribution of the underlying waveform. We apply our method on
simulated data from a network of advanced ground-based detectors and
demonstrate the gravitational wave signal reconstruction. We study the
reconstruction quality for different binary configurations and equations of
state for the colliding neutron stars. We show how our method can be used to
constrain the yet-uncertain equation of state of neutron star matter. The
constraints on the equation of state we derive are complimentary to
measurements of the tidal deformation of the colliding neutron stars during the
late inspiral phase. In the case of a non-detection of a post-merger signal
following a binary neutron star inspiral we show that we can place upper limits
on the energy emitted.Comment: 11 pages, 12 figures, final published versio
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