11,026 research outputs found
Enhancing the significance of gravitational wave bursts through signal classification
The quest to observe gravitational waves challenges our ability to
discriminate signals from detector noise. This issue is especially relevant for
transient gravitational waves searches with a robust eyes wide open approach,
the so called all- sky burst searches. Here we show how signal classification
methods inspired by broad astrophysical characteristics can be implemented in
all-sky burst searches preserving their generality. In our case study, we apply
a multivariate analyses based on artificial neural networks to classify waves
emitted in compact binary coalescences. We enhance by orders of magnitude the
significance of signals belonging to this broad astrophysical class against the
noise background. Alternatively, at a given level of mis-classification of
noise events, we can detect about 1/4 more of the total signal population. We
also show that a more general strategy of signal classification can actually be
performed, by testing the ability of artificial neural networks in
discriminating different signal classes. The possible impact on future
observations by the LIGO-Virgo network of detectors is discussed by analysing
recoloured noise from previous LIGO-Virgo data with coherent WaveBurst, one of
the flagship pipelines dedicated to all-sky searches for transient
gravitational waves
Searching for periodic sources with LIGO. II: Hierarchical searches
The detection of quasi-periodic sources of gravitational waves requires the
accumulation of signal-to-noise over long observation times. If not removed,
Earth-motion induced Doppler modulations, and intrinsic variations of the
gravitational-wave frequency make the signals impossible to detect. These
effects can be corrected (removed) using a parameterized model for the
frequency evolution. We compute the number of independent corrections
required for incoherent search strategies which use stacked
power spectra---a demodulated time series is divided into segments of
length , each segment is FFTed, the power is computed, and the
spectra are summed up. We estimate that the sensitivity of an all-sky search
that uses incoherent stacks is a factor of 2--4 better than would be achieved
using coherent Fourier transforms; incoherent methods are computationally
efficient at exploring large parameter spaces. A two-stage hierarchical search
which yields another 20--60% improvement in sensitivity in all-sky searches for
old (>= 1000 yr) slow (= 40 yr) fast (<=
1000 Hz) pulsars. Assuming 10^{12} flops of effective computing power for data
analysis, enhanced LIGO interferometers should be sensitive to: (i) Galactic
core pulsars with gravitational ellipticities of \epsilon\agt5\times 10^{-6}
at 200 Hz, (ii) Gravitational waves emitted by the unstable r-modes of newborn
neutron stars out to distances of ~8 Mpc, and (iii) neutron stars in LMXB's
with x-ray fluxes which exceed . Moreover,
gravitational waves from the neutron star in Sco X-1 should be detectable is
the interferometer is operated in a signal-recycled, narrow-band configuration.Comment: 22 Pages, 13 Figure
Matched filtering of gravitational waves from inspiraling compact binaries: Computational cost and template placement
We estimate the number of templates, computational power, and storage
required for a one-step matched filtering search for gravitational waves from
inspiraling compact binaries. These estimates should serve as benchmarks for
the evaluation of more sophisticated strategies such as hierarchical searches.
We use waveform templates based on the second post-Newtonian approximation for
binaries composed of nonspinning compact bodies in circular orbits. We present
estimates for six noise curves: LIGO (three configurations), VIRGO, GEO600, and
TAMA. To search for binaries with components more massive than 0.2M_o while
losing no more than 10% of events due to coarseness of template spacing,
initial LIGO will require about 1*10^11 flops (floating point operations per
second) for data analysis to keep up with data acquisition. This is several
times higher than estimated in previous work by Owen, in part because of the
improved family of templates and in part because we use more realistic (higher)
sampling rates. Enhanced LIGO, GEO600, and TAMA will require computational
power similar to initial LIGO. Advanced LIGO will require 8*10^11 flops, and
VIRGO will require 5*10^12 flops. If the templates are stored rather than
generated as needed, storage requirements range from 1.5*10^11 real numbers for
TAMA to 6*10^14 for VIRGO. We also sketch and discuss an algorithm for placing
the templates in the parameter space.Comment: 15 pages, 4 figures, submitted to Phys. Rev.
A Solution to the Galactic Foreground Problem for LISA
Low frequency gravitational wave detectors, such as the Laser Interferometer
Space Antenna (LISA), will have to contend with large foregrounds produced by
millions of compact galactic binaries in our galaxy. While these galactic
signals are interesting in their own right, the unresolved component can
obscure other sources. The science yield for the LISA mission can be improved
if the brighter and more isolated foreground sources can be identified and
regressed from the data. Since the signals overlap with one another we are
faced with a ``cocktail party'' problem of picking out individual conversations
in a crowded room. Here we present and implement an end-to-end solution to the
galactic foreground problem that is able to resolve tens of thousands of
sources from across the LISA band. Our algorithm employs a variant of the
Markov Chain Monte Carlo (MCMC) method, which we call the Blocked Annealed
Metropolis-Hastings (BAM) algorithm. Following a description of the algorithm
and its implementation, we give several examples ranging from searches for a
single source to searches for hundreds of overlapping sources. Our examples
include data sets from the first round of Mock LISA Data Challenges.Comment: 19 pages, 27 figure
A Proposed Search for the Detection of Gravitational Waves from Eccentric Binary Black Holes
Most of compact binary systems are expected to circularize before the
frequency of emitted gravitational waves (GWs) enters the sensitivity band of
the ground based interferometric detectors. However, several mechanisms have
been proposed for the formation of binary systems, which retain eccentricity
throughout their lifetimes. Since no matched-filtering algorithm has been
developed to extract continuous GW signals from compact binaries on orbits with
low to moderate values of eccentricity, and available algorithms to detect
binaries on quasi-circular orbits are sub-optimal to recover these events, in
this paper we propose a search method for detection of gravitational waves
produced from the coalescences of eccentric binary black holes (eBBH). We study
the search sensitivity and the false alarm rates on a segment of data from the
second joint science run of LIGO and Virgo detectors, and discuss the
implications of the eccentric binary search for the advanced GW detectors
Sliding coherence window technique for hierarchical detection of continuous gravitational waves
A novel hierarchical search technique is presented for all-sky surveys for
continuous gravitational-wave sources, such as rapidly spinning nonaxisymmetric
neutron stars. Analyzing yearlong detector data sets over realistic ranges of
parameter space using fully coherent matched-filtering is computationally
prohibitive. Thus more efficient, so-called hierarchical techniques are
essential. Traditionally, the standard hierarchical approach consists of
dividing the data into nonoverlapping segments of which each is coherently
analyzed and subsequently the matched-filter outputs from all segments are
combined incoherently. The present work proposes to break the data into
subsegments shorter than the desired maximum coherence time span (size of the
coherence window). Then matched-filter outputs from the different subsegments
are efficiently combined by sliding the coherence window in time: Subsegments
whose timestamps are closer than coherence window size are combined coherently,
otherwise incoherently. Compared to the standard scheme at the same coherence
time baseline, data sets longer by about 50-100% would have to be analyzed to
achieve the same search sensitivity as with the sliding coherence window
approach. Numerical simulations attest to the analytically estimated
improvement.Comment: 11 pages, 4 figure
Gravitational waves: search results, data analysis and parameter estimation
The Amaldi 10 Parallel Session C2 on gravitational wave (GW) search results, data analysis and parameter estimation included three lively sessions of lectures by 13 presenters, and 34 posters. The talks and posters covered a huge range of material, including results and analysis techniques for ground-based GW detectors, targeting anticipated signals from different astrophysical sources: compact binary inspiral, merger and ringdown; GW bursts from intermediate mass binary black hole mergers, cosmic string cusps, core-collapse supernovae, and other unmodeled sources; continuous waves from spinning neutron stars; and a stochastic GW background. There was considerable emphasis on Bayesian techniques for estimating the parameters of coalescing compact binary systems from the gravitational waveforms extracted from the data from the advanced detector network. This included methods to distinguish deviations of the signals from what is expected in the context of General Relativity
Use of the MultiNest algorithm for gravitational wave data analysis
We describe an application of the MultiNest algorithm to gravitational wave
data analysis. MultiNest is a multimodal nested sampling algorithm designed to
efficiently evaluate the Bayesian evidence and return posterior probability
densities for likelihood surfaces containing multiple secondary modes. The
algorithm employs a set of live points which are updated by partitioning the
set into multiple overlapping ellipsoids and sampling uniformly from within
them. This set of live points climbs up the likelihood surface through nested
iso-likelihood contours and the evidence and posterior distributions can be
recovered from the point set evolution. The algorithm is model-independent in
the sense that the specific problem being tackled enters only through the
likelihood computation, and does not change how the live point set is updated.
In this paper, we consider the use of the algorithm for gravitational wave data
analysis by searching a simulated LISA data set containing two non-spinning
supermassive black hole binary signals. The algorithm is able to rapidly
identify all the modes of the solution and recover the true parameters of the
sources to high precision.Comment: 18 pages, 4 figures, submitted to Class. Quantum Grav; v2 includes
various changes in light of referee's comment
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