6,821 research outputs found
An Overview of Gravitational-Wave Sources
We review current best estimates of the strength and detectability of the gravitational waves from a variety of sources, for both ground-based and space-based detectors, and we describe the information carried by the waves
An improved, "phase-relaxed" F-statistic for gravitational-wave data analysis
Rapidly rotating, slightly non-axisymmetric neutron stars emit nearly
periodic gravitational waves (GWs), quite possibly at levels detectable by
ground-based GW interferometers. We refer to these sources as "GW pulsars". For
any given sky position and frequency evolution, the F-statistic is the optimal
(frequentist) statistic for the detection of GW pulsars. However, in "all-sky"
searches for previously unknown GW pulsars, it would be computationally
intractable to calculate the (fully coherent) F-statistic at every point of a
(suitably fine) grid covering the parameter space: the number of gridpoints is
many orders of magnitude too large for that. Here we introduce a
"phase-relaxed" F-statistic, which we denote F_pr, for incoherently combining
the results of fully coherent searches over short time intervals. We estimate
(very roughly) that for realistic searches, our F_pr is ~10-15% more sensitive
than the "semi-coherent" F-statistic that is currently used. Moreover, as a
byproduct of computing F_pr, one obtains a rough determination of the
time-evolving phase offset between one's template and the true signal imbedded
in the detector noise. Almost all the ingredients that go into calculating F_pr
are already implemented in LAL, so we expect that relatively little additional
effort would be required to develop a search code that uses F_pr.Comment: 8 pages, 4 figures, submitted to PR
Application of dust for space structures
Physical properties and applications of dust structures in space technolog
Report on the first round of the Mock LISA Data Challenges
The Mock LISA Data Challenges (MLDCs) have the dual purpose of fostering the development of LISA data analysis tools and capabilities, and demonstrating the technical readiness already achieved by the gravitational-wave community in distilling a rich science payoff from the LISA data output. The first round of MLDCs has just been completed: nine challenges consisting of data sets containing simulated gravitational-wave signals produced either by galactic binaries or massive black hole binaries embedded in simulated LISA instrumental noise were released in June 2006 with deadline for submission of results at the beginning of December 2006. Ten groups have participated in this first round of challenges. All of the challenges had at least one entry which successfully characterized the signal to better than 95% when assessed via a correlation with phasing ambiguities accounted for. Here, we describe the challenges, summarize the results and provide a first critical assessment of the entries
Regularization of second-order scalar perturbation produced by a point-particle with a nonlinear coupling
Accurate calculation of the motion of a compact object in a background
spacetime induced by a supermassive black hole is required for the future
detection of such binary systems by the gravitational-wave detector LISA.
Reaching the desired accuracy requires calculation of the second-order
gravitational perturbations produced by the compact object. At the point
particle limit the second-order gravitational perturbation equations turn out
to have highly singular source terms, for which the standard retarded solutions
diverge. Here we study a simplified scalar toy-model in which a point particle
induces a nonlinear scalar field in a given curved spacetime. The corresponding
second-order scalar perturbation equation in this model is found to have a
similar singular source term, and therefore its standard retarded solutions
diverge. We develop a regularization method for constructing well-defined
causal solutions for this equation. Notably these solutions differ from the
standard retarded solutions, which are ill-defined in this case.Comment: 14 page
Towards the solution of the relativistic gravitational radiation reaction problem for binary black holes
Here we present the results of applying the generalized Riemann zeta-function
regularization method to the gravitational radiation reaction problem. We
analyze in detail the headon collision of two nonspinning black holes with
extreme mass ratio. The resulting reaction force on the smaller hole is
repulsive. We discuss the possible extensions of these method to generic orbits
and spinning black holes. The determination of corrected trajectories allows to
add second perturbative corrections with the consequent increase in the
accuracy of computed waveforms.Comment: Contribution to the Proceedings of the 3rd LISA Symposiu
Showcasing the Translingual SL/FL Classroom: Strategies, Practices, and Beliefs
In an article published in this journal 15 years ago, Vivian Cook argued that it was time to question the time-honoured view that the native language (NL) should be avoided in the classroom by teachers and students. The justifications for this perspective hinged on a questionable compartmentalization of the two languages in the mind. The conventional wisdom has been that the NL has no place in the second language (SL) or foreign language (FL) classroom and that teachers should focus on getting students to think and interact exclusively in the target language (TL). In Linguistic Imperialism, Phillipson debunks five fallacies that are foundational in the field of applied linguistics, among them, the monolingual fallacy or the idea that a second or foreign language is best taught monolingually. Questioning monolingual pedagogies is at the heart of the investigations assembled in this Special Issue
The Effect of the LISA Response Function on Observations of Monochromatic Sources
The Laser Interferometer Space Antenna (LISA) is expected to provide the
largest observational sample of binary systems of faint sub-solar mass compact
objects, in particular white-dwarfs, whose radiation is monochromatic over most
of the LISA observational window. Current astrophysical estimates suggest that
the instrument will be able to resolve about 10000 such systems, with a large
fraction of them at frequencies above 3 mHz, where the wavelength of
gravitational waves becomes comparable to or shorter than the LISA arm-length.
This affects the structure of the so-called LISA transfer function which cannot
be treated as constant in this frequency range: it introduces characteristic
phase and amplitude modulations that depend on the source location in the sky
and the emission frequency. Here we investigate the effect of the LISA transfer
function on detection and parameter estimation for monochromatic sources. For
signal detection we show that filters constructed by approximating the transfer
function as a constant (long wavelength approximation) introduce a negligible
loss of signal-to-noise ratio -- the fitting factor always exceeds 0.97 -- for
f below 10mHz, therefore in a frequency range where one would actually expect
the approximation to fail. For parameter estimation, we conclude that in the
range 3mHz to 30mHz the errors associated with parameter measurements differ
from about 5% up to a factor of 10 (depending on the actual source parameters
and emission frequency) with respect to those computed using the long
wavelength approximation.Comment: replacement version with typos correcte
Angular Resolution of the LISA Gravitational Wave Detector
We calculate the angular resolution of the planned LISA detector, a
space-based laser interferometer for measuring low-frequency gravitational
waves from galactic and extragalactic sources. LISA is not a pointed
instrument; it is an all-sky monitor with a quadrupolar beam pattern. LISA will
measure simultaneously both polarization components of incoming gravitational
waves, so the data will consist of two time series. All physical properties of
the source, including its position, must be extracted from these time series.
LISA's angular resolution is therefore not a fixed quantity, but rather depends
on the type of signal and on how much other information must be extracted.
Information about the source position will be encoded in the measured signal in
three ways: 1) through the relative amplitudes and phases of the two
polarization components, 2) through the periodic Doppler shift imposed on the
signal by the detector's motion around the Sun, and 3) through the further
modulation of the signal caused by the detector's time-varying orientation. We
derive the basic formulae required to calculate the LISA's angular resolution
for a given source. We then evaluate for
two sources of particular interest: monchromatic sources and mergers of
supermassive black holes. For these two types of sources, we calculate (in the
high signal-to-noise approximation) the full variance-covariance matrix, which
gives the accuracy to which all source parameters can be measured. Since our
results on LISA's angular resolution depend mainly on gross features of the
detector geometry, orbit, and noise curve, we expect these results to be fairly
insensitive to modest changes in detector design that may occur between now and
launch. We also expect that our calculations could be easily modified to apply
to a modified design.Comment: 15 pages, 5 figures, RevTex 3.0 fil
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