1,622 research outputs found
Subtraction of Newtonian Noise Using Optimized Sensor Arrays
Fluctuations in the local Newtonian gravitational field present a limit to
high precision measurements, including searches for gravitational waves using
laser interferometers. In this work, we present a model of this perturbing
gravitational field and evaluate schemes to mitigate the effect by estimating
and subtracting it from the interferometer data stream. Information about the
Newtonian noise is obtained from simulated seismic data. The method is tested
on causal as well as acausal implementations of noise subtraction. In both
cases it is demonstrated that broadband mitigation factors close to 10 can be
achieved removing Newtonian noise as a dominant noise contribution. The
resulting improvement in the detector sensitivity will substantially enhance
the detection rate of gravitational radiation from cosmological sources.Comment: 29 pages, 11 figure
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.Comment: 16 pages, 7 figures, published in ApJ. Reformatted preprint with
emulateap
Model-independent test of gravity with a network of ground-based gravitational-wave detectors
The observation of gravitational waves with a global network of
interferometric detectors such as advanced LIGO, advanced Virgo, and KAGRA will
make it possible to probe into the nature of space-time structure. Besides
Einstein's general theory of relativity, there are several theories of
gravitation that passed experimental tests so far. The gravitational-wave
observation provides a new experimental test of alternative theories of gravity
because a gravitational wave may have at most six independent modes of
polarization, of which properties and number of modes are dependent on theories
of gravity. This paper proposes a method to reconstruct the independent modes
of polarization in time-series data of an advanced detector network. Since the
method does not rely on any specific model, it gives model-independent test of
alternative theories of gravity
Bayesian inference on compact binary inspiral gravitational radiation signals in interferometric data
Presented is a description of a Markov chain Monte Carlo (MCMC) parameter
estimation routine for use with interferometric gravitational radiational data
in searches for binary neutron star inspiral signals. Five parameters
associated with the inspiral can be estimated, and summary statistics are
produced. Advanced MCMC methods were implemented, including importance
resampling and prior distributions based on detection probability, in order to
increase the efficiency of the code. An example is presented from an
application using realistic, albeit fictitious, data.Comment: submitted to Classical and Quantum Gravity. 14 pages, 5 figure
Doppler effect in TianQin time-delay interferometry
The current design of space-based gravitational wave detectors utilizes
heterodyne laser interferometry in inter-satellite science measurements.
Frequency variations of the heterodyne beatnotes are predominantly caused by
the Doppler effect from relative satellite motion along lines of sight.
Generally considered to be outside the measurement band, this Doppler frequency
shift appears to have been overlooked in numerical simulations of time-delay
interferometry (TDI). However, the potential impact on the implementation of
TDI should be assessed. The issue is particularly relevant to TianQin that
features geocentric orbits, because of strong gravity disturbances from the
Earth-Moon system at frequencies Hz. In this
proof-of-principle study, based on high-precision orbital data obtained from
detailed gravity field modeling, we incorporate the Doppler shift in the
generation of TianQin's beatnote phase signals. To remove the large-scale
Doppler phase drift at frequencies Hz, we develop a
high-performance high-pass filter and consider two possible processing
sequences, i.e., applying the filter before or after TDI combinations. Our
simulation results favor the former and demonstrate successful removal of the
low-frequency gravity disturbances for TianQin without degrading the TDI
performance, assuming 10 m pseudo-ranging uncertainty. The filtering scheme can
be used in developing the initial noise-reduction pipeline for TianQin.Comment: 10 pages, 11 figures, revised to match the version accepted by Phys.
Rev.
BICEP2 II: Experiment and Three-Year Data Set
We report on the design and performance of the BICEP2 instrument and on its
three-year data set. BICEP2 was designed to measure the polarization of the
cosmic microwave background (CMB) on angular scales of 1 to 5 degrees
(=40-200), near the expected peak of the B-mode polarization signature of
primordial gravitational waves from cosmic inflation. Measuring B-modes
requires dramatic improvements in sensitivity combined with exquisite control
of systematics. The BICEP2 telescope observed from the South Pole with a 26~cm
aperture and cold, on-axis, refractive optics. BICEP2 also adopted a new
detector design in which beam-defining slot antenna arrays couple to
transition-edge sensor (TES) bolometers, all fabricated on a common substrate.
The antenna-coupled TES detectors supported scalable fabrication and
multiplexed readout that allowed BICEP2 to achieve a high detector count of 500
bolometers at 150 GHz, giving unprecedented sensitivity to B-modes at degree
angular scales. After optimization of detector and readout parameters, BICEP2
achieved an instrument noise-equivalent temperature of 15.8 K sqrt(s). The
full data set reached Stokes Q and U map depths of 87.2 nK in square-degree
pixels (5.2 K arcmin) over an effective area of 384 square degrees within
a 1000 square degree field. These are the deepest CMB polarization maps at
degree angular scales to date. The power spectrum analysis presented in a
companion paper has resulted in a significant detection of B-mode polarization
at degree scales.Comment: 30 pages, 24 figure
A Brief Analysis of Gravitational Search Algorithm (GSA) Publication from 2009 to May 2013
Gravitational Search Algorithm was introduced in year 2009. Since its introduction, the academic community shows a
great interest on this algorith. This can be seen by the high number of publications with a short span of time. This paper analyses the publication trend of Gravitational Search Algorithm since its introduction until May 2013. The objective of this paper is to give exposure to reader the publication trend in the area of Gravitational Search Algorithm
Time-delay interferometric ranging for LISA: Statistical analysis of bias-free ranging using laser noise minimization
Die Laser Interferometer Space Antenna (LISA) ist eine Mission der europĂ€ischen Weltraumagentur (ESA) zur Detektion von Gravitationswellen im Frequenzbereich zwischen 10^-4 Hz und 1 Hz. Gravitationswellen induzieren relative AbstandsĂ€nderungen, die LISA mithilfe von Laserinterferometrie mit PicometerprĂ€zision misst. Ein groĂes Problem hierbei ist das Frequenzrauschen der Laser. Um dieses zu unterdrĂŒcken, ist es notwendig, mithilfe eines Algorithmus namens TDI (engl. time-delay interferometry), virtuelle Interferometer mit gleichlangen Armen zu konstruieren, wie z.B. das klassische Michelson-Interferometer.
In dieser Arbeit untersuchen wir die Performanz von TDI unter realistischen Bedingungen und identifizieren verschiedene Kopplungsmechanismen des Laserfrequenzrauschens. Als erstes betrachten wir die Datenverarbeitung an Bord der Satelliten, die benötigt wird, um die Abtastrate der interferometrischen Messungen zu reduzieren. HierfĂŒr sind Anti-Alias-Filter vorgesehen, die der Faltung von Laserrauschleistung in das Beobachtungsband vorbeugen. AuĂerdem wirkt sich die Ebenheit der Filter auf die EffektivitĂ€t von TDI aus (engl. flexing-filtering-effect). Dieser Effekt ist bereits in der Literatur beschrieben und wir demonstrieren in dieser Arbeit die Möglichkeit, ihn mithilfe von Kompensationsfiltern effektiv zu reduzieren. Als zweites betrachten wir Kopplungsmechanismen von Laserfrequenzrauschen im TDI-Algorithmus selbst. Fehler in der Interpolation der interferometrischen Messungen und Ungenauigkeiten in den absoluten Abstandsmessungen zwischen den Satelliten fĂŒhren ebenfalls zu einer unzureichenden Reduzierung des Laserfrequenzrauschens. Wir beschreiben die oben genannten Kopplungsmechanismen analytisch und validieren die zugrundeliegenden Modelle mithilfe von numerischen Simulationen. Das tiefere VerstĂ€ndnis dieser Residuen ermöglicht es uns, geeignete instrumentelle Parameter zu wĂ€hlen, die von hoher Relevanz fĂŒr das Missionsdesign von LISA sind.
Des Weiteren beschĂ€ftigen wir uns in dieser Arbeit mit der möglichst genauen Bestimmung der absoluten AbstĂ€nden zwischen den Satelliten, die fĂŒr den TDI Algorithmus erforderlich sind. HierfĂŒr werden die Abstandsinformationen aus den SeitenbĂ€ndern und der PRN-Modulation (engl. pseudo-random noise) kombiniert. Wir zeigen, dass die PRN-Messung von systematischen Verzerrungen betroffen ist, die zu Laserrauschresiduen in den TDI-Variablen fĂŒhren. Um diesen Fehler zu korrigieren, schlagen wir als zusĂ€tzliche Abstandsmessung TDI-Ranging (TDI-R) vor. TDI-R ist zwar ungenauer, aber frei von systematischen Verzerrungen und kann daher zur Kalibrierung der PRN-Messungen herangezogen werden. Wir prĂ€sentieren in dieser Arbeit eine ausfĂŒhrliche statistische Studie, um die Performanz von TDI-R zu charakterisieren. DafĂŒr formulieren wir die Likelihood-Funktion der interferometrischen Messungen und berechnen die Fisher-Informationsmatrix, um die theoretisch mögliche untere Grenze der SchĂ€tzvarianz zu finden. Diese verhĂ€lt sich invers proportional zur Integrationszeit und dem VerhĂ€ltnis von SekundĂ€rrauschleistung, die die interferometrische Messung fundamental limitiert, und Laserrauschleistung. ZusĂ€tzlich validieren wir die analytische untere Grenze der SchĂ€tzvarianz mithilfe von numerischen Simulationen und zeigen damit, dass unsere Implementierung von TDI-R optimal ist. Der entwickelte TDI-R-Algorithmus wird Teil der Datenverarbeitungspipeline sein und KonsistenzprĂŒfungen und Kalibrierung der primĂ€ren Abstandsmessmethoden ermöglichen.The Laser Interferometer Space Antenna (LISA) is a future ESA-led space-based observatory to explore the gravitational universe in the frequency band between 10^-4 Hz and 1 Hz. LISA implements picometer-precise inter-satellite ranging to measure tiny ripples in spacetime induced by gravitational waves (GWs). However, the single-link measurements are dominated by laser frequency noise, which is about nine orders of magnitude larger than the GW signals. Therefore, in post-processing, the time-delay interferometry (TDI) algorithm is used to synthesize virtual equal-arm interferometers to suppress laser frequency noise.
In this work we identify several laser frequency noise coupling channels that limit the performance of TDI. First, the on-board processing, which is used to decimate the sampling rate from tens of megahertz down to the telemetry rate of a few hertz, requires careful design. Appropriate anti-aliasing filters must be implemented to mitigate folding of laser noise power into the observation band. Furthermore, the flatness of these filters is important to limit the impact of the flexing-filtering effect. We demonstrate that this effect can be effectively reduced by using compensation filters on ground. Second, the post-processing delays applied in TDI are subject to interpolation and ranging errors. We study these laser and timing noise residuals analytically and perform simulations to validate the models numerically. Our findings have direct implications for the design of the LISA instrument as we identify the instrumental parameters that are essential for successful laser noise suppression and provide methods for designing appropriate filters for the on-board processing.
In addition, we discuss a dedicated ranging processing pipeline that produces high-precision range estimates that are the input for TDI by combining the sideband and pseudo-random noise (PRN) ranges. We show in this thesis that biases in the PRN measurements limit the laser noise suppression performance. Therefore, we propose time-delay interferometric ranging (TDI-R) as a third ranging sensor to estimate bias-free ranges that can be used to calibrate the biases in the PRN measurements.
We present a thorough statistical study of TDI-R to evaluate its performance. Therefore, we formulate the likelihood function of the interferometric data and use the Fisher information formalism to find a lower bound on the estimation variance of the inter-satellite ranges. We find that the ranging uncertainty is proportional to the inverse of the integration time and the ratio of secondary noise power, that limits the interferometric readout, to the laser noise power. To validate our findings we implement prototype TDI-R pipelines and perform numerical simulations. We show that we are able to formulate optimal estimators of the unbiased range that reach the Cramér-Rao lower bound previously expressed analytically. The developed TDI-R pipeline will be integrated into the ranging processing pipeline to perform consistency checks and ensure well-calibrated inter-satellite ranges
Towards detecting gravitational waves from the Crab Pulsar
Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Physics, 2009.Includes bibliographical references (leaf 47).A variety of fundamental and technical noise sources impact the ability of the Laser Interferometer Gravitational-Wave Observatory (LIGO) to directly detect gravitational radiation. Noteworthy examples include Newtonian gravity gradient, seismic, acoustic, thermal and photon shot noise. These are the obstacles that must be confronted by the planned upgrade to the LIGO detectors, Advanced LIGO. To achieve improved sensitivity, significant improvements of LIGO's hardware must be paralleled by equivalent advances in the digital realm. Using adaptive filtering techniques, it is possible to cancel noise from known sources. We present results showing successful suppression of power line noise at 60Hz by a factor of 500 using commonly available sensors and standard FIR filters. Attenuation of 60Hz noise is particularly important to LIGO due to the 59.7 Hz radiation frequency of the Crab pulsar. Application of the techniques developed in this work to the LIGO detectors promises to improve the signal to noise ratio at the Crab frequency and thus pave the way toward direct detection of gravitational radiation from a known source.by Sharon Rapoport.S.B
Classification and Recovery of Radio Signals from Cosmic Ray Induced Air Showers with Deep Learning
Radio emission from air showers enables measurements of cosmic particle
kinematics and identity. The radio signals are detected in broadband Megahertz
antennas among continuous background noise. We present two deep learning
concepts and their performance when applied to simulated data. The first
network classifies time traces as signal or background. We achieve a true
positive rate of about 90% for signal-to-noise ratios larger than three with a
false positive rate below 0.2%. The other network is used to clean the time
trace from background and to recover the radio time trace originating from an
air shower. Here we achieve a resolution in the energy contained in the trace
of about 20% without a bias for of the traces with a signal. The
obtained frequency spectrum is cleaned from signals of radio frequency
interference and shows the expected shape.Comment: 20 pages, 13 figures, resubmitted to JINS
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