96 research outputs found
Search method for long-duration gravitational-wave transients from neutron stars
We introduce a search method for a new class of gravitational-wave signals,
namely long-duration O(hours - weeks) transients from spinning neutron stars.
We discuss the astrophysical motivation from glitch relaxation models and we
derive a rough estimate for the maximal expected signal strength based on the
superfluid excess rotational energy. The transient signal model considered here
extends the traditional class of infinite-duration continuous-wave signals by a
finite start-time and duration. We derive a multi-detector Bayes factor for
these signals in Gaussian noise using \F-statistic amplitude priors, which
simplifies the detection statistic and allows for an efficient implementation.
We consider both a fully coherent statistic, which is computationally limited
to directed searches for known pulsars, and a cheaper semi-coherent variant,
suitable for wide parameter-space searches for transients from unknown neutron
stars. We have tested our method by Monte-Carlo simulation, and we find that it
outperforms orthodox maximum-likelihood approaches both in sensitivity and in
parameter-estimation quality.Comment: 20 pages, 9 figures; submitted to PR
Matching matched filtering with deep networks in gravitational-wave astronomy
We report on the construction of a deep convolutional neural network that can
reproduce the sensitivity of a matched-filtering search for binary black hole
gravitational-wave signals. The standard method for the detection of well
modeled transient gravitational-wave signals is matched filtering. However, the
computational cost of such searches in low latency will grow dramatically as
the low frequency sensitivity of gravitational-wave detectors improves.
Convolutional neural networks provide a highly computationally efficient method
for signal identification in which the majority of calculations are performed
prior to data taking during a training process. We use only whitened time
series of measured gravitational-wave strain as an input, and we train and test
on simulated binary black hole signals in synthetic Gaussian noise
representative of Advanced LIGO sensitivity. We show that our network can
classify signal from noise with a performance that emulates that of match
filtering applied to the same datasets when considering the sensitivity defined
by Reciever-Operator characteristics.Comment: 5 pages, 3 figures, submitted to PR
Data Analysis Methods for Testing Alternative Theories of Gravity with LISA Pathfinder
In this paper we present a data analysis approach applicable to the potential
saddle-point fly-by mission extension of LISA Pathfinder (LPF). At the peak of
its sensitivity, LPF will sample the gravitational field in our Solar System
with a precision of several at frequencies
around . Such an accurate accelerometer will allow us to test
alternative theories of gravity that predict deviations from Newtonian dynamics
in the non-relativistic limit. As an example, we consider the case of the
Tensor-Vector-Scalar theory of gravity and calculate, within the
non-relativistic limit of this theory, the signals that anomalous tidal
stresses generate in LPF. We study the parameter space of these signals and
divide it into two subgroups, one related to the mission parameters and the
other to the theory parameters that are determined by the gravity model. We
investigate how the mission parameters affect the signal detectability
concluding that these parameters can be determined with the sufficient
precision from the navigation of the spacecraft and fixed during our analysis.
Further, we apply Bayesian parameter estimation and determine the accuracy to
which the gravity theory parameters may be inferred. We evaluate the portion of
parameter space that may be eliminated in case of no signal detection and
estimate the detectability of signals as a function of parameter space
location. We also perform a first investigation of non-Gaussian
"noise-glitches" that may occur in the data. The analysis we develop is
universal and may be applied to anomalous tidal stress induced signals
predicted by any theory of gravity
Host redshifts from gravitational-wave observations of binary neutron star mergers
Inspiralling compact binaries as standard sirens will soon become an
invaluable tool for cosmology when advanced interferometric gravitational-wave
detectors begin their observations in the coming years. However, a degeneracy
in the information carried by gravitational waves between the total rest-frame
mass and the redshift of the source implies that neither can be
directly extracted from the signal, but only the combination , the
redshifted mass. Recent work has shown that for binary neutron star systems, a
tidal correction to the gravitational-wave phase in the late-inspiral signal
that depends on the rest-frame source mass could be used to break the
mass-redshift degeneracy. We propose here to use the signature encoded in the
post-merger signal to deduce the redshift to the source. This will allow an
accurate extraction of the intrinsic rest-frame mass of the source, in turn
permitting the determination of source redshift and luminosity distance solely
from gravitational-wave observations. This will herald a new era in precision
cosmography and astrophysics. Using numerical simulations of binary neutron
star mergers of very slightly different mass, we model gravitational-wave
signals at different redshifts and use Bayesian parameter estimation to
determine the accuracy with which the redshift can be extracted for a source of
known mass. We find that the Einstein Telescope can determine the source
redshift to -- at redshifts of .Comment: 10 pages, 4 figures; same as the version before except for
acknowledgment
Bayesian versus frequentist upper limits
While gravitational waves have not yet been measured directly, data analysis
from detection experiments commonly includes an upper limit statement. Such
upper limits may be derived via a frequentist or Bayesian approach; the
theoretical implications are very different, and on the technical side, one
notable difference is that one case requires maximization of the likelihood
function over parameter space, while the other requires integration. Using a
simple example (detection of a sinusoidal signal in white Gaussian noise), we
investigate the differences in performance and interpretation, and the effect
of the "trials factor", or "look-elsewhere effect".Comment: http://cdsweb.cern.ch/record/1306523/files/CERN-2011-006.pdf,
http://indico.cern.ch/materialDisplay.py?contribId=52&materialId=paper&confId=10774
Rapid parameter estimation for an all-sky continuous gravitational wave search using conditional varitational auto-encoders
All-sky searches for continuous gravitational waves are generally model
dependent and computationally costly to run. By contrast, SOAP is a
model-agnostic search that rapidly returns candidate signal tracks in the
time-frequency plane. In this work we extend the SOAP search to return broad
Bayesian posteriors on the astrophysical parameters of a specific signal model.
These constraints drastically reduce the volume of parameter space that any
follow-up search needs to explore, so increasing the speed at which candidates
can be identified and confirmed. Our method uses a machine learning technique,
specifically a conditional variational auto-encoder, and delivers a rapid
estimation of the posterior distribution of the four Doppler parameters of a
continuous wave signal. It does so without requiring a clear definition of a
likelihood function, or being shown any true Bayesian posteriors in training.
We demonstrate how the Doppler parameter space volume can be reduced by a
factor of for signals of SNR 100
A robust machine learning algorithm to search for continuous gravitational waves
Many continuous gravitational wave searches are affected by instrumental
spectral lines that could be confused with a continuous astrophysical signal.
Several techniques have been developed to limit the effect of these lines by
penalising signals that appear in only a single detector. We have developed a
general method, using a convolutional neural network, to reduce the impact of
instrumental artefacts on searches that use the SOAP algorithm. The method can
identify features in corresponding frequency bands of each detector and
classify these bands as containing a signal, an instrumental line, or noise. We
tested the method against four different data-sets: Gaussian noise with time
gaps, data from the final run of Initial LIGO (S6) with signals added, the
reference S6 mock data challenge data set and signals injected into data from
the second advanced LIGO observing run (O2). Using the S6 mock data challenge
data set and at a 1% false alarm probability we showed that at 95% efficiency a
fully-automated SOAP search has a sensitivity corresponding to a coherent
signal-to-noise ratio of 110, equivalent to a sensitivity depth of 10
Hz, making this automated search competitive with other searches
requiring significantly more computing resources and human intervention
Detection and Classification of Supernova Gravitational Waves Signals: A Deep Learning Approach
We demonstrate the application of a convolutional neural network to the
gravitational wave signals from core collapse supernovae. Using simulated time
series of gravitational wave detectors, we show that based on the explosion
mechanisms, a convolutional neural network can be used to detect and classify
the gravitational wave signals buried in noise. For the waveforms used in the
training of the convolutional neural network, our results suggest that a
network of advanced LIGO, advanced VIRGO and KAGRA, or a network of LIGO A+,
advanced VIRGO and KAGRA is likely to detect a magnetorotational core collapse
supernovae within the Large and Small Magellanic Clouds, or a Galactic event if
the explosion mechanism is the neutrino-driven mechanism. By testing the
convolutional neural network with waveforms not used for training, we show that
the true alarm probabilities are 52% and 83% at 60 kpc for waveforms R3E1AC and
R4E1FC L. For waveforms s20 and SFHx at 10 kpc, the true alarm probabilities
are 70% and 93% respectively. All at false alarm probability equal to 10%
Cosmological inference using only gravitational wave observations of binary neutron stars
Gravitational waves emitted during the coalescence of binary neutron star systems are self-calibrating signals. As such, they can provide a direct measurement of the luminosity distance to a source without the need for a cross-calibrated cosmic distance-scale ladder. In general, however, the corresponding redshift measurement needs to be obtained via electromagnetic observations since it is totally degenerate with the total mass of the system. Nevertheless, Fisher matrix studies have shown that, if information about the equation of state of the neutron stars is available, it is possible to extract redshift information from the gravitational wave signal alone. Therefore, measuring the cosmological parameters in pure gravitational-wave fashion is possible. Furthermore, the huge number of sources potentially observable by the Einstein Telescope has led to speculations that the gravitational wave measurement is potentially competitive with traditional methods. The Einstein Telescope is a conceptual study for a third generation gravitational wave detector which is designed to yield 10^3–10^7 detections of binary neutron star systems per year. This study presents the first Bayesian investigation of the accuracy with which the cosmological parameters can be measured using information coming only from the gravitational wave observations of binary neutron star systems by the Einstein Telescope. We find, by direct simulation of 10^3 detections of binary neutron stars, that, within our simplifying assumptions, H_0, Ω_m, Ω_Λ, w_0 and w_1 can be measured at the 95% level with an accuracy of ∼8% , 65%, 39%, 80% and 90%, respectively. We also find, by extrapolation, that a measurement accuracy comparable with current measurements by Planck is possible if the number of gravitational wave events observed is O(10^(6–7)) . We conclude that, while not competitive with electromagnetic missions in terms of significant digits, gravitational waves alone are capable of providing a complementary determination of the dynamics of the Universe
- …