918 research outputs found
Report on an all-sky LIGO search for periodic gravitational waves in the S4 data
We report on an all-sky search with the LIGO detectors for periodic
gravitational waves in the frequency range 50-1000 Hz and having a negative
frequency time derivative with magnitude between zero and Hz/s. Data
from the fourth LIGO science run have been used in this search. Three different
semi-coherent methods of summing strain power were applied. Observing no
evidence for periodic gravitational radiation, we report upper limits on strain
amplitude and interpret these limits to constrain radiation from rotating
neutron stars.Comment: 5 pages, 1 figure, presented at Amaldi7, Sydney (July 2007
Gravitational Wave Detection by Interferometry (Ground and Space)
Significant progress has been made in recent years on the development of
gravitational wave detectors. Sources such as coalescing compact binary
systems, neutron stars in low-mass X-ray binaries, stellar collapses and
pulsars are all possible candidates for detection. The most promising design of
gravitational wave detector uses test masses a long distance apart and freely
suspended as pendulums on Earth or in drag-free craft in space. The main theme
of this review is a discussion of the mechanical and optical principles used in
the various long baseline systems in operation around the world - LIGO (USA),
Virgo (Italy/France), TAMA300 and LCGT (Japan), and GEO600 (Germany/U.K.) - and
in LISA, a proposed space-borne interferometer. A review of recent science runs
from the current generation of ground-based detectors will be discussed, in
addition to highlighting the astrophysical results gained thus far. Looking to
the future, the major upgrades to LIGO (Advanced LIGO), Virgo (Advanced Virgo),
LCGT and GEO600 (GEO-HF) will be completed over the coming years, which will
create a network of detectors with significantly improved sensitivity required
to detect gravitational waves. Beyond this, the concept and design of possible
future "third generation" gravitational wave detectors, such as the Einstein
Telescope (ET), will be discussed.Comment: Published in Living Reviews in Relativit
Revisiting special relativity: A natural algebraic alternative to Minkowski spacetime
Minkowski famously introduced the concept of a space-time continuum in 1908,
merging the three dimensions of space with an imaginary time dimension , with the unit imaginary producing the correct spacetime distance , and the results of Einstein's then recently developed theory of special
relativity, thus providing an explanation for Einstein's theory in terms of the
structure of space and time. As an alternative to a planar Minkowski space-time
of two space dimensions and one time dimension, we replace the unit imaginary , with the Clifford bivector for the plane
that also squares to minus one, but which can be included without the addition
of an extra dimension, as it is an integral part of the real Cartesian plane
with the orthonormal basis and . We find that with this model of
planar spacetime, using a two-dimensional Clifford multivector, the spacetime
metric and the Lorentz transformations follow immediately as properties of the
algebra. This also leads to momentum and energy being represented as components
of a multivector and we give a new efficient derivation of Compton's scattering
formula, and a simple formulation of Dirac's and Maxwell's equations. Based on
the mathematical structure of the multivector, we produce a semi-classical
model of massive particles, which can then be viewed as the origin of the
Minkowski spacetime structure and thus a deeper explanation for relativistic
effects. We also find a new perspective on the nature of time, which is now
given a precise mathematical definition as the bivector of the plane.Comment: 29 pages, 2 figure
Physics, Astrophysics and Cosmology with Gravitational Waves
Gravitational wave detectors are already operating at interesting sensitivity
levels, and they have an upgrade path that should result in secure detections
by 2014. We review the physics of gravitational waves, how they interact with
detectors (bars and interferometers), and how these detectors operate. We study
the most likely sources of gravitational waves and review the data analysis
methods that are used to extract their signals from detector noise. Then we
consider the consequences of gravitational wave detections and observations for
physics, astrophysics, and cosmology.Comment: 137 pages, 16 figures, Published version
<http://www.livingreviews.org/lrr-2009-2
Detection Confidence Tests for Burst and Inspiral Candidate Events
The LIGO Scientific Collaboration (LSC) is developing and running analysis
pipelines to search for gravitational-wave transients emitted by astrophysical
events such as compact binary mergers or core-collapse supernovae. However,
because of the non-Gaussian, non-stationary nature of the noise exhibited by
the LIGO detectors, residual false alarms might be found at the end of the
pipelines. A critical aspect of the search is then to assess our confidence for
gravitational waves and to distinguish them from those false alarms. Both the
'Compact Binary Coalescence' and the 'Burst' working groups have been
developing a detection checklist for the validation of candidate-events,
consisting of a series of tests which aim to corroborate a detection or to
eliminate a false alarm. These tests include for example data quality checks,
analysis of the candidate appearance, parameter consistency studies and
coherent analysis. In this paper, the general methodology used for candidate
validation is presented. The method is illustrated with an example of simulated
gravitational-wave signal and a false alarm.Comment: 15 pages, 8 figures, Contribution to 12th Gravitational Wave Data
Analysis Workshop. Version sent to Classical and Quantum Gravity immediately
before publication. It addresses the CQG referee's comment
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All-sky search for short gravitational-wave bursts in the second Advanced LIGO and Advanced Virgo run
We present the results of a search for short-duration gravitational-wave transients in the data from the second observing run of Advanced LIGO and Advanced Virgo. We search for gravitational-wave transients with a duration of milliseconds to approximately one second in the 32-4096 Hz frequency band with minimal assumptions about the signal properties, thus targeting a wide variety of sources. We also perform a matched-filter search for gravitational-wave transients from cosmic string cusps for which the waveform is well modeled. The unmodeled search detected gravitational waves from several binary black hole mergers which have been identified by previous analyses. No other significant events have been found by either the unmodeled search or the cosmic string search. We thus present the search sensitivities for a variety of signal waveforms and report upper limits on the source rate density as a function of the characteristic frequency of the signal. These upper limits are a factor of 3 lower than the first observing run, with a 50% detection probability for gravitational-wave emissions with energies of ∼10-9 Mc2 at 153 Hz. For the search dedicated to cosmic string cusps we consider several loop distribution models, and present updated constraints from the same search done in the first observing run
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Search for Eccentric Binary Black Hole Mergers with Advanced LIGO and Advanced Virgo during Their First and Second Observing Runs
When formed through dynamical interactions, stellar-mass binary black holes (BBHs) may retain eccentric orbits (e > 0.1 at 10 Hz) detectable by ground-based gravitational-wave detectors. Eccentricity can therefore be used to differentiate dynamically formed binaries from isolated BBH mergers. Current template-based gravitational-wave searches do not use waveform models associated with eccentric orbits, rendering the search less efficient for eccentric binary systems. Here we present the results of a search for BBH mergers that inspiral in eccentric orbits using data from the first and second observing runs (O1 and O2) of Advanced LIGO and Advanced Virgo. We carried out the search with the coherent WaveBurst algorithm, which uses minimal assumptions on the signal morphology and does not rely on binary waveform templates. We show that it is sensitive to binary mergers with a detection range that is weakly dependent on eccentricity for all bound systems. Our search did not identify any new binary merger candidates. We interpret these results in light of eccentric binary formation models. We rule out formation channels with rates ⪆100 Gpc-3 yr-1 for e > 0.1, assuming a black hole mass spectrum with a power-law index ≲2
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Search for gravitational waves from Scorpius X-1 in the second Advanced LIGO observing run with an improved hidden Markov model
We present results from a semicoherent search for continuous gravitational
waves from the low-mass X-ray binary Scorpius X-1, using a hidden Markov model
(HMM) to track spin wandering. This search improves on previous HMM-based
searches of LIGO data by using an improved frequency domain matched filter, the
-statistic, and by analysing data from Advanced LIGO's second
observing run. In the frequency range searched, from to
, we find no evidence of gravitational radiation. At
, the most sensitive search frequency, we report an upper
limit on gravitational wave strain (at 95\% confidence) of when marginalising over source inclination angle. This is the
most sensitive search for Scorpius X-1, to date, that is specifically designed
to be robust in the presence of spin wandering
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