arXiv subjects

Drew Keppel

Publications and source records attributed to Drew Keppel.

At least 19 recordsLinked to original sources

arXiv2017

Application of a Zero-latency Whitening Filter to Compact Binary Coalescence Gravitational-wave Searches

Joint electromagnetic and gravitational-wave (GW) observation is a major goal of both the GW astronomy and electromagnetic astronomy communities for the coming decade. One way to accomplish this goal is to direct follow-up of GW candidates. Prompt electromagnetic emission may fade quickly, therefore it is desirable to have GW detection happen as quickly as possible. A leading source of latency in GW detection is the whitening of the data. We examine the performance of a zero-latency whitening filter in a detection pipeline for compact binary coalescence (CBC) GW signals. We find that the filter reproduces signal-to-noise ratio (SNR) sufficiently consistent with the results of the original high-latency and phase-preserving filter for both noise and artificial GW signals (called "injections"). Additionally, we demonstrate that these two whitening filters show excellent agreement in $\chi^2$ value, a discriminator for GW signals.

astro-ph.IM↗

arXiv2017

Analysis Framework for the Prompt Discovery of Compact Binary Mergers in Gravitational-wave Data

We describe a stream-based analysis pipeline to detect gravitational waves from the merger of binary neutron stars, binary black holes, and neutron-star-black-hole binaries within ~ 1 minute of the arrival of the merger signal at Earth. Such low-latency detection is crucial for the prompt response by electromagnetic facilities in order to observe any fading electromagnetic counterparts that might be produced by mergers involving at least one neutron star. Even for systems expected not to produce counterparts, low-latency analysis of the data is useful for deciding when not to point telescopes, and as feedback to observatory operations. Analysts using this pipeline were the first to identify GW151226, the second gravitational-wave event ever detected. The pipeline also operates in an offline mode, in which it incorporates more refined information about data quality and employs acausal methods that are inapplicable to the online mode. The pipeline's offline mode was used in the detection of the first two gravitational-wave events, GW150914 and GW151226, as well as the identification of a third candidate, LVT151012.

astro-ph.IM↗

arXiv2016

The PyCBC search for gravitational waves from compact binary coalescence

We describe the PyCBC search for gravitational waves from compact-object binary coalescences in advanced gravitational-wave detector data. The search was used in the first Advanced LIGO observing run and unambiguously identified two black hole binary mergers, GW150914 and GW151226. At its core, the PyCBC search performs a matched-filter search for binary merger signals using a bank of gravitational-wave template waveforms. We provide a complete description of the search pipeline including the steps used to mitigate the effects of noise transients in the data, identify candidate events and measure their statistical significance. The analysis is able to measure false-alarm rates as low as one per million years, required for confident detection of signals. Using data from initial LIGO's sixth science run, we show that the new analysis reduces the background noise in the search, giving a 30% increase in sensitive volume for binary neutron star systems over previous searches.

gr-qc↗

arXiv2014

Accuracy of gravitational waveform models for observing neutron-star--black-hole binaries in Advanced LIGO

Gravitational waves radiated by the coalescence of compact-object binaries containing a neutron star and a black hole are one of the most interesting sources for the ground-based gravitational-wave observatories Advanced LIGO and Advanced Virgo. Advanced LIGO will be sensitive to the inspiral of a $1.4\, M_\odot$ neutron star into a $10\,M_\odot$ black hole to a maximum distance of $\sim 900$ Mpc. Achieving this sensitivity and extracting the physics imprinted in observed signals requires accurate modeling of the binary to construct template waveforms. In a NSBH binary, the black hole may have significant angular momentum (spin), which affects the phase evolution of the emitted gravitational waves. We investigate the ability of post-Newtonian (PN) templates to model the gravitational waves emitted during the inspiral phase of NSBH binaries. We restrict the black hole's spin to be aligned with the orbital angular momentum and compare several approximants. We examine restricted amplitude waveforms that are accurate to 3.5PN order in the orbital dynamics and complete to 2.5PN order in the spin dynamics. We also consider PN waveforms with the recently derived 3.5PN spin-orbit and 3PN spin-orbit tail corrections. We compare these approximants to the effective-one-body model. For all these models, large disagreements start at low to moderate black hole spins, particularly for binaries where the spin is anti-aligned with the orbital angular momentum. We show that this divergence begins in the early inspiral at $v \sim 0.2$ for $χ_{BH} \sim 0.4$. PN spin corrections beyond those currently known will be required for optimal detection searches and to measure the parameters of neutron star--black hole binaries. While this complicates searches, the strong dependence of the gravitational-wave signal on the spin dynamics will make it possible to extract significant astrophysical information.

gr-qc↗

arXiv2014

Toward Early-Warning Detection of Gravitational Waves from Compact Binary Coalescence

Rapid detection of compact binary coalescence (CBC) with a network of advanced gravitational-wave detectors will offer a unique opportunity for multi-messenger astronomy. Prompt detection alerts for the astronomical community might make it possible to observe the onset of electromagnetic emission from (CBC). We demonstrate a computationally practical filtering strategy that could produce early-warning triggers before gravitational radiation from the final merger has arrived at the detectors.

astro-ph.IM↗

arXiv2013

Statistical and systematic errors for gravitational-wave inspiral signals: A principal component analysis

Identifying the source parameters from a gravitational-wave measurement alone is limited by our ability to discriminate signals from different sources and the accuracy of the waveform family employed in the search. Here we address both issues in the framework of an adapted coordinate system that allows for linear Fisher-matrix type calculations of waveform differences that are both accurate and computationally very efficient. We investigate statistical errors by using principal component analysis of the post-Newtonian (PN) expansion coefficients, which is well conditioned despite the Fisher matrix becoming ill conditioned for larger numbers of parameters. We identify which combinations of physical parameters are most effectively measured by gravitational-wave detectors for systems of neutron stars and black holes with aligned spin. We confirm the expectation that the dominant parameter of the inspiral waveform is the chirp mass. The next dominant parameter depends on a combination of the spin and the symmetric mass ratio. In addition, we can study the systematic effect of various spin contributions to the PN phasing within the same parametrization, showing that the inclusion of spin-orbit corrections up to next-to-leading order, but not necessarily of spin-spin contributions, is crucial for an accurate inspiral waveform model. This understanding of the waveform structure throughout the parameter space is important to set up an efficient search strategy and correctly interpret future gravitational-wave observations.

gr-qc↗

arXiv2013

Metrics for multi-detector template placement in searches for short-duration nonprecessing inspiral gravitational-wave signals

Using the family of multi-detector F-statistic metrics for short duration, nonprecessing inspiral signals, we derive a marginalized metric that is directly applicable to the problem of generating template banks for coincident and coherent multi-detector searches for gravitational-waves. This metric is compared to other average metrics, such as that proposed for the case of searches associated with continuous signals from rotating neutron stars. We show how the four-dimensional metric can be separated into two two-dimensional metrics associated with the sky and mass parameter subspaces, allowing the creation of separate template banks for these subspaces. Finally, we present an algorithm for computing the mass space metric associated with both coincident and coherent multi-detector targeted or all-sky searches for short duration, nonprecessing inspiral gravitational-wave signals.

gr-qc↗

arXiv2013

Parameter space metric for 3.5 post-Newtonian gravitational-waves from compact binary inspirals

We derive the metric on the parameter space of 3.5 post-Newtonian (3.5PN) stationary phase compact binary inspiral waveforms for a single detector, neglecting spin, eccentricity, and finite-body effects. We demonstrate that this leads to better template placement than the current practice of using the 2PN metric to place 3.5PN templates: The recovered event rate is improved by about 10% at a cost of nearly doubling the number of templates. The cross-correlations between mass parameters are also more accurate, which will result in better coincidence tests.

gr-qc↗

arXiv2013

The balancing act of template bank construction: inspiral waveform template banks for gravitational-wave detectors and optimizations at fixed computational cost

Gravitational-wave searches for signals from inspiralling compact binaries have relied on matched filtering banks of waveforms (called template banks) to try to extract the signal waveforms from the detector data. These template banks have been constructed using four main considerations, the region of parameter space of interest, the sensitivity of the detector, the matched filtering bandwidth, and the sensitivity one is willing to lose due to the granularity of template placement, the latter of which is governed by the minimal match. In this work we describe how the choice of the lower frequency cutoff, the lower end of the matched filter frequency band, can be optimized for detection. We also show how the minimal match can be optimally chosen in the case of limited computational resources. These techniques are applied to searches for binary neutron star signals that have been previously performed when analyzing Initial LIGO and Virgo data and will be performed analyzing Advanced LIGO and Advanced Virgo data using the expected detector sensitivity. By following the algorithms put forward here, the volume sensitivity of these searches is predicted to improve without increasing the computational cost of performing the search.

physics.data-an↗

arXiv2012

Interpolation in waveform space: enhancing the accuracy of gravitational waveform families using numerical relativity

Matched-filtering for the identification of compact object mergers in gravitational-wave antenna data involves the comparison of the data stream to a bank of template gravitational waveforms. Typically the template bank is constructed from phenomenological waveform models since these can be evaluated for an arbitrary choice of physical parameters. Recently it has been proposed that singular value decomposition (SVD) can be used to reduce the number of templates required for detection. As we show here, another benefit of SVD is its removal of biases from the phenomenological templates along with a corresponding improvement in their ability to represent waveform signals obtained from numerical relativity (NR) simulations. Using these ideas, we present a method that calibrates a reduced SVD basis of phenomenological waveforms against NR waveforms in order to construct a new waveform approximant with improved accuracy and faithfulness compared to the original phenomenological model. The new waveform family is given numerically through the interpolation of the projection coefficients of NR waveforms expanded onto the reduced basis and provides a generalized scheme for enhancing phenomenological models.

gr-qc↗

arXiv2012

A method to estimate the significance of coincident gravitational-wave observations from compact binary coalescence

Coalescing compact binary systems consisting of neutron stars and/or black holes should be detectable with upcoming advanced gravitational-wave detectors such as LIGO, Virgo, GEO and {KAGRA}. Gravitational-wave experiments to date have been riddled with non-Gaussian, non-stationary noise that makes it challenging to ascertain the significance of an event. A popular method to estimate significance is to time shift the events collected between detectors in order to establish a false coincidence rate. Here we propose a method for estimating the false alarm probability of events using variables commonly available to search candidates that does not rely on explicitly time shifting the events while still capturing the non-Gaussianity of the data. We present a method for establishing a statistical detection of events in the case where several silver-plated (3--5$σ$) events exist but not necessarily any gold-plated ($>5σ$) events. We use LIGO data and a simulated, realistic, blind signal population to test our method.

gr-qc↗

arXiv2012

The multi-detector F-statistic metric for short-duration non-precessing inspiral gravitational-wave signals

We derive explicit expressions for the multi-detector F-statistic metric applied to short-duration non-precessing inspiral signals. This is required for template bank production associated with coherent searches for short-duration non-precessing inspiral signals in gravitational-wave data from a network of detectors. We compare the metric's performance with explicit overlap calculations for all relevant dimensions of parameter space and find the metric accurately predicts the loss of detection statistic above overlaps of 95%. We also show the effect that neglecting the variations of the detector response functions has on the metric.

gr-qc↗

arXiv2012

Detecting transient gravitational waves in non-Gaussian noise with partially redundant analysis methods

There is a broad class of astrophysical sources that produce detectable, transient, gravitational waves. Some searches for transient gravitational waves are tailored to known features of these sources. Other searches make few assumptions about the sources. Typically events are observable with multiple search techniques. This work describes how to combine the results of searches that are not independent, treating each search as a classifier for a given event. This will be shown to improve the overall sensitivity to gravitational-wave events while directly addressing the problem of consistent interpretation of multiple trials.

gr-qc↗

arXiv2012

Likelihood-ratio ranking of gravitational-wave candidates in a non-Gaussian background

We describe a general approach to detection of transient gravitational-wave signals in the presence of non-Gaussian background noise. We prove that under quite general conditions, the ratio of the likelihood of observed data to contain a signal to the likelihood of it being a noise fluctuation provides optimal ranking for the candidate events found in an experiment. The likelihood-ratio ranking allows us to combine different kinds of data into a single analysis. We apply the general framework to the problem of unifying the results of independent experiments and the problem of accounting for non-Gaussian artifacts in the searches for gravitational waves from compact binary coalescence in LIGO data. We show analytically and confirm through simulations that in both cases the likelihood ratio statistic results in an improved analysis.

gr-qc↗

arXiv2012

Use of Singular-Value Decomposition in Gravitational-Wave Data Analysis

Singular-value decomposition is a powerful technique that has been used in the analysis of matrices in many fields. In this paper, we summarize how it has been applied to the analysis of gravitational-wave data. These include producing basis waveforms for matched filtering, decreasing the computational cost of searching for many waveforms, improving parameter estimation, and providing a method of waveform interpolation.

physics.data-an↗

arXiv2011

Interpolating compact binary waveforms using the singular value decomposition

Compact binary systems with total masses between tens and hundreds of solar masses will produce gravitational waves during their merger phase that are detectable by second-generation ground-based gravitational-wave detectors. In order to model the gravitational waveform of the merger epoch of compact binary coalescence, the full Einstein equations must be solved numerically for the entire mass and spin parameter space. However, this is computationally expensive. Several models have been proposed to interpolate the results of numerical relativity simulations. In this paper we propose a numerical interpolation scheme that stems from the singular value decomposition. This algorithm shows promise in allowing one to construct arbitrary waveforms within a certain parameter space given a sufficient density of numerical simulations covering the same parameter space. We also investigate how similar approaches could be used to interpolate waveforms in the context of parameter estimation.

gr-qc↗

arXiv2011

Efficiently enclosing the compact binary parameter space by singular-value decomposition

Gravitational-wave searches for the merger of compact binaries use matched-filtering as the method of detecting signals and estimating parameters. Such searches construct a fine mesh of filters covering a signal parameter space at high density. Previously it has been shown that singular value decomposition can reduce the effective number of filters required to search the data. Here we study how the basis provided by the singular value decomposition changes dimension as a function of template bank density. We will demonstrate that it is sufficient to use the basis provided by the singular value decomposition of a low density bank to accurately reconstruct arbitrary points within the boundaries of the template bank. Since this technique is purely numerical it may have applications to interpolating the space of numerical relativity waveforms.

gr-qc↗

arXiv2011

Composite gravitational-wave detection of compact binary coalescence

The detection of gravitational waves from compact binaries relies on a computationally burdensome processing of gravitational-wave detector data. The parameter space of compact-binary-coalescence gravitational waves is large and optimal detection strategies often require nearly redundant calculations. Previously, it has been shown that singular value decomposition of search filters removes redundancy. Here we will demonstrate the use of singular value decomposition for a composite detection statistic. This can greatly improve the prospects for a computationally feasible rapid detection scheme across a large compact binary parameter space.

physics.data-an↗