Publications (20)3.32 Total impact
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Article: Continuous Gravitational Waves from Isolated Galactic Neutron Stars in the Advanced Detector Era
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ABSTRACT: We consider a simulated population of isolated Galactic neutron stars. The rotational frequency of each neutron star evolves through a combination of electromagnetic and gravitational wave emission. The magnetic field strength dictates the dipolar emission, and the ellipticity (a measure of a neutron star's deformation) dictates the gravitational wave emission. Through both analytic and numerical means, we assess the detectability of the Galactic neutron star population and bound the magnetic field strength and ellipticity parameter space of Galactic neutron stars with or without a direct gravitational wave detection. While our simulated population is primitive, this work establishes a framework by which future efforts can be conducted.09/2012; -
Article: Toward Making Epidemiologic Data More Useful for Quantitative Risk Assessment
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ABSTRACT: This paper discusses issues faced in using epidemiologic data to develop quantitative estimates of risk from specified patterns of exposure to a toxicant. We focus on use of data from cohort studies with binary endpoints (occurrence or non-occurrence of disease). Relative advantages of Cox regression and Poisson regression are presented. A general form of exposure metric is presented, and criteria for selecting an appropriate metric are discussed. Advantages and disadvantages of various dose-response models are discussed. It is argued that, unless low-dose linearity of the dose response can be ruled out on non-statistical grounds, then bounds for low-dose risk should incorporate low-dose linearity; a sequential procedure for computing such bounds is illustrated. Limitations in exposure data and their impact on risk assessments are discussed. Issues arising when using meta-analytic techniques to combine data from multiple epidemiologic studies are discussed. Limitations in risk assessments resulting from reliance upon published results alone are described. Methods for converting from measures of risk used in epidemiologic studies (e.g., relative risk) to measures appropriate for a risk assessment (e.g., additional lifetime probability of disease occurrence resulting from a specific exposure pattern) are described in detail. Several examples from the asbestos epidemiologic literature are presented to illustrate these issues.The Open Epidemiology Journal 01/2011; 411:30-44. -
Article: Blandford’s argument: The strongest continuous gravitational wave signal
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ABSTRACT: For a uniform population of neutron stars whose spin-down is dominated by the emission of gravitational radiation, an old argument of Blandford states that the expected gravitational-wave amplitude of the nearest source is independent of the deformation and rotation frequency of the objects. Recent work has improved and extended this argument to set upper limits on the expected amplitude from neutron stars that also emit electromagnetic radiation. We restate these arguments in a more general framework, and simulate the evolution of such a population of stars in the gravitational potential of our galaxy. The simulations allow us to test the assumptions of Blandford’s argument on a realistic model of our galaxy. We show that the two key assumptions of the argument (two dimensionality of the spatial distribution and a steady-state frequency distribution) are in general not fulfilled. The effective scaling dimension D of the spatial distribution of neutron stars is significantly larger than two, and for frequencies detectable by terrestrial instruments the frequency distribution is not in a steady state unless the ellipticity is unrealistically large. Thus, in the cases of most interest, the maximum expected gravitational-wave amplitude does have a strong dependence on the deformation and rotation frequency of the population. The results strengthen the previous upper limits on the expected gravitational-wave amplitude from neutron stars by a factor of 6 for realistic values of ellipticity.Phys. Rev. D. 08/2008; 78(4). -
Article: Publisher's Note: Upper limits on gravitational wave emission from 78 radio pulsars [Phys. Rev. D 76, 042001 (2007)]
Phys. Rev. D. 01/2008; 77(6):069905. -
Article: FINDCHIRP: an algorithm for detection of gravitational waves from inspiraling compact binaries
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ABSTRACT: Matched-filter searches for gravitational waves from coalescing compact binaries by the LIGO Scientific Collaboration use the findchirp algorithm: an implementation of the optimal filter with innovations to account for unknown signal parameters and to improve performance on detector data that has non-stationary and non-Gaussian artifacts. We provide details on the methods used in the findchirp algorithm as used in the search for sub-solar mass binaries, binary neutron stars, neutron star--black hole binaries and binary black holes.09/2005; -
Article: Making h(t) for LIGO
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ABSTRACT: The conversion of the read-out from the anti-symmetric port of the LIGO interferometers into gravitational strain has thus far been performed in the frequency domain. Here we describe a conversion in the time domain which is based on the method developed by GEO. We illustrate the method using the Hanford 4km interferometer during the second LIGO science run (S2). Comment: 14 pages, 8 figures05/2004; -
Conference Proceeding: LIGO: S1 Science Results and Plans Beyond
Proceedings of the Thirteenth Workshop on General Relativity and Gravitation in Japan, http://www.scientificcommons.org/20565483; 01/2004 -
Conference Proceeding: LIGO: S1 Science Results and Plans Beyond
Proceedings of the Thirteenth Workshop on General Relativity and Gravitation in Japan, http://www.scientificcommons.org/20565483; 01/2004 -
Article: Towards the first search for a stochastic background in LIGO data: applications of signal simulations
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ABSTRACT: We describe the utility of simulated-signal injection studies on earth-based gravitational-wave (GW) interferometric data toward obtaining bounds on the strength of a stochastic GW background. The existence of such a background today is predicted by several cosmological models, but with varying strengths and power spectra. Earth-based detectors, such as LIGO, will eventually achieve enough sensitivity to start constraining some of these models through these bounds. A significant part of the effort to use LIGO data to place such bounds is to estimate the efficiency of the data analysis pipeline in detecting the variety of predicted backgrounds. We took the data taking opportunity offered by the first science run at LIGO to inject simulated signals of varying strengths both in hardware as well as software. We describe here the results obtained in searching for these injection backgrounds. We discuss especially those results that either varied from the expected ones or are crucial to the search for a stochastic GW background. The reasons behind the variations are also explained.Classical and Quantum Gravity 08/2003; 20(17):S677. · 3.32 Impact Factor -
Article: Optimal Strategies for Sinusoidal Signal Detection
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ABSTRACT: We derive and study optimal and nearly-optimal strategies for the detection of sinusoidal signals hidden in additive (Gaussian and non-Gaussian) noise. Such strategies are an essential part of algorithms for the detection of the gravitational Continuous Wave (CW) signals produced by pulsars. Optimal strategies are derived for the case where the signal phase is not known and the product of the signal frequency and the observation time is non-integral. Comment: 18 pages, REVTEX4, 7 figures, 2 tables06/2002; -
Article: Robust statistics for deterministic and stochastic gravitational waves in non-Gaussian noise. II: Bayesian analyses
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ABSTRACT: In a previous paper (gr-qc/0105100) we derived a set of near-optimal signal detection techniques for gravitational wave detectors whose noise probability distributions contain non-Gaussian tails. The methods modify standard methods by truncating sample values which lie in those non-Gaussian tails. The methods were derived, in the frequentist framework, by minimizing false alarm probabilities at fixed false detection probability in weak signal limit. For stochastic signals, the resulting statistic consisted of a sum of an auto-correlation term and a cross-correlation term; it was necessary to discard by hand the auto-correlation term to obtain the correct, generalized cross-correlation statistic. In the present paper, we present an alternative Bayesian derivation of the same signal detection techniques. We compute the probability that a signal is present in the data, in the limit where the signal-to-noise ratio squared per frequency bin is small, where the integrated signal-to-noise ratio is large compared to one, and where the total probability in the non-Gaussian tail part of the noise distribution is small. We show that, for each model considered, the resulting probability is to a good approximation a monotonic function of the detection statistic derived in the previous paper. Moreover, for stochastic signals, the new Bayesian derivation automatically eliminates the problematic auto-correlation term. Comment: revtex, 13 pages, no figures05/2002; -
Article: Robust statistics for deterministic and stochastic gravitational waves in non-Gaussian noise I: Frequentist analyses
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ABSTRACT: Gravitational wave detectors will need optimal signal-processing algorithms to extract weak signals from the detector noise. Most algorithms designed to date are based on the unrealistic assumption that the detector noise may be modeled as a stationary Gaussian process. However most experiments exhibit a non-Gaussian ``tail'' in the probability distribution. This ``excess'' of large signals can be a troublesome source of false alarms. This article derives an optimal (in the Neyman-Pearson sense, for weak signals) signal processing strategy when the detector noise is non-Gaussian and exhibits tail terms. This strategy is robust, meaning that it is close to optimal for Gaussian noise but far less sensitive than conventional methods to the excess large events that form the tail of the distribution. The method is analyzed for two different signal analysis problems: (i) a known waveform (e.g., a binary inspiral chirp) and (ii) a stochastic background, which requires a multi-detector signal processing algorithm. The methods should be easy to implement: they amount to truncation or clipping of sample values which lie in the outlier part of the probability distribution. Comment: RevTeX 4, 17 pages, 8 figures, typos corrected from first versions05/2001; -
Article: Is the squeezing of relic gravitational waves produced by inflation detectable?
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ABSTRACT: Grishchuk has shown that the stochastic background of gravitational waves produced by an inflationary phase in the early Universe has an unusual property: it is not a stationary Gaussian random process. Due to squeezing, the phases of the different waves are correlated in a deterministic way, arising from the process of parametric amplification that created them. The resulting random process is Gaussian but non-stationary. This provides a unique signature that could in principle distinguish a background created by inflation from stationary stochastic backgrounds created by other types of processes. We address the question: could this signature be observed with a gravitational wave detector? Sadly, the answer appears to be "no": an experiment which could distinguish the non-stationary behavior would have to last approximately the age of the Universe at the time of measurement. This rules out direct detection by ground and space based gravitational wave detectors, but not indirect detections via the electromagnetic Cosmic Microwave Background Radiation (CMBR). Comment: 17 pages, 4 Postscript figures, uses revtex, psfig, to be submitted to PRD, minor revisions - appendix B clarified, corrected typos, added references06/1999; -
Article: Detecting a stochastic background of gravitational radiation: Signal processing strategies and sensitivities
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ABSTRACT: We analyze the signal processing required for the optimal detection of a stochastic background of gravitational radiation using laser interferometric detectors. Starting with basic assumptions about the statistical properties of a stochastic gravity-wave background, we derive expressions for the optimal filter function and signal-to-noise ratio for the cross-correlation of the outputs of two gravity-wave detectors. Sensitivity levels required for detection are then calculated. Issues related to: (i) calculating the signal-to-noise ratio for arbitrarily large stochastic backgrounds, (ii) performing the data analysis in the presence of nonstationary detector noise, (iii) combining data from multiple detector pairs to increase the sensitivity of a stochastic background search, (iv) correlating the outputs of 4 or more detectors, and (v) allowing for the possibility of correlated noise in the outputs of two detectors are discussed. We briefly describe a computer simulation which mimics the generation and detection of a simulated stochastic gravity-wave signal in the presence of simulated detector noise. Numerous graphs and tables of numerical data for the five major interferometers (LIGO-WA, LIGO-LA, VIRGO, GEO-600, and TAMA-300) are also given. The treatment given in this paper should be accessible to both theorists involved in data analysis and experimentalists involved in detector design and data acquisition. Comment: 81 pages, 30 postscript figures, REVTEX10/1997; -
Article: Merlin cluster - report for the BAR
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ABSTRACT: This is the report to the BAR that contains the design specifications for the cluster that the GEO data analysis group at the AEI is planning to build in order to perform searches for continuous gravitational wave signals. -
Article: Detector description and performance for the first coincidence observations between LIGO and GEO
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ABSTRACT: For 17 days in August and September 2002, the LIGO and GEO interferometer gravitational wave detectors were operated in coincidence to produce their first data for scientific analysis. Although the detectors were still far from their design sensitivity levels, the data can be used to place better upper limits on the flux of gravitational waves incident on the earth than previous direct measurements. This paper describes the instruments and the data in some detail, as a companion to analysis papers based on the first data.Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, v.517, 154-179 (2004). -
Article: Upper limits on the strength of periodic gravitational waves from PSR J1939+2134
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ABSTRACT: The first science run of the LIGO and GEO gravitational wave detectors presented the opportunity to test methods of searching for gravitational waves from known pulsars. Here we present new direct upper limits on the strength of waves from the pulsar PSR J1939+2134 using two independent analysis methods, one in the frequency domain using frequentist statistics and one in the time domain using Bayesian inference. Both methods show that the strain amplitude at Earth from this pulsar is less than a few times 10-22.Classical and Quantum Gravity, v.21, S671-S676 (2004). -
Article: The Einstein@Home search for periodic gravitational waves in early S5 LIGO data
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ABSTRACT: This paper reports on an all-sky search for periodic gravitational waves from sources such as deformed isolated rapidly spinning neutron stars. The analysis uses 840 hours of data from 66 days of the fifth LIGO science run (S5). The data were searched for quasimonochromatic waves with frequencies f in the range from 50 to 1500 Hz, with a linear frequency drift f-dot (measured at the solar system barycenter) in the range -f/tau<f-dot <0.1f/tau, for a minimum spin-down age tau of 1000 years for signals below 400 Hz and 8000 years above 400 Hz. The main computational work of the search was distributed over approximately 100 000 computers volunteered by the general public. This large computing power allowed the use of a relatively long coherent integration time of 30 hours while searching a large parameter space. This search extends Einstein@Home's previous search in LIGO S4 data to about 3 times better sensitivity. No statistically significant signals were found. In the 125–225 Hz band, more than 90% of sources with dimensionless gravitational-wave strain tensor amplitude greater than 3×10-24 would have been detected.Physical Review D, v.80 (2009). -
Article: Erratum: Beating the spin-down limit on gravitational wave emission from the Crab pulsar
Astrophysical Journal Letters, v.706, L203-L204 (2009). -
Article: The Einstein@Home search for periodic gravitational waves in LIGO S4 data
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ABSTRACT: A search for periodic gravitational waves, from sources such as isolated rapidly-spinning neutron stars, was carried out using 510 hours of data from the fourth LIGO science run (S4). The search was for quasi-monochromatic waves in the frequency range from 50 Hz to 1500 Hz, with a linear frequency drift f-dot (measured at the solar system barycenter) in the range -f/tau < f-dot < 0.1 f/tau, where the minimum spin-down age tau was 1000 years for signals below 300 Hz and 10000 years above 300 Hz. The main computational work of the search was distributed over approximately 100000 computers volunteered by the general public. This large computing power allowed the use of a relatively long coherent integration time of 30 hours, despite the large parameter space searched. No statistically significant signals were found. The sensitivity of the search is estimated, along with the fraction of parameter space that was vetoed because of contamination by instrumental artifacts. In the 100 Hz to 200 Hz band, more than 90% of sources with dimensionless gravitational wave strain amplitude greater than 1e-23 would have been detected.Physical Review D, v.79 (2009).
Top co-authors
Top Journals
Institutions
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2011
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University of North Carolina at Chapel Hill
Chapel Hill, NC, USA -
Louisiana Tech University
Ruston, LA, USA
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2008
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Max-Planck-Institut für Gravitationsphysik (Albert-Einstein-Institut)
Potsdam, Brandenburg, Germany
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1997–2005
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University of Wisconsin - Milwaukee
- Department of Physics
Milwaukee, WI, USA
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