71 research outputs found
Hierarchical Hough all-sky search for periodic gravitational waves in LIGO S5 data
We describe a new pipeline used to analyze the data from the fifth science
run (S5) of the LIGO detectors to search for continuous gravitational waves
from isolated spinning neutron stars. The method employed is based on the Hough
transform, which is a semi-coherent, computationally efficient, and robust
pattern recognition technique. The Hough transform is used to find signals in
the time-frequency plane of the data whose frequency evolution fits the pattern
produced by the Doppler shift imposed on the signal by the Earth's motion and
the pulsar's spin-down during the observation period. The main differences with
respect to previous Hough all-sky searches are described. These differences
include the use of a two-step hierarchical Hough search, analysis of
coincidences among the candidates produced in the first and second year of S5,
and veto strategies based on a test.Comment: 7 pages, 2 figures, Amaldi08 proceedings, submitted to JPC
Searching for gravitational waves from Cassiopeia A with LIGO
We describe a search underway for periodic gravitational waves from the
central compact object in the supernova remnant Cassiopeia A. The object is the
youngest likely neutron star in the Galaxy. Its position is well known, but the
object does not pulse in any electromagnetic radiation band and thus presents a
challenge in searching the parameter space of frequency and frequency
derivatives. We estimate that a fully coherent search can, with a reasonable
amount of time on a computing cluster, achieve a sensitivity at which it is
theoretically possible (though not likely) to observe a signal even with the
initial LIGO noise spectrum. Cassiopeia A is only the second object after the
Crab pulsar for which this is true. The search method described here can also
obtain interesting results for similar objects with current LIGO sensitivity.Comment: 8 pages, 1 figure; accepted to Classical and Quantum Gravit
First LIGO search for gravitational wave bursts from cosmic (super)strings
We report on a matched-filter search for gravitational wave bursts from
cosmic string cusps using LIGO data from the fourth science run (S4) which took
place in February and March 2005. No gravitational waves were detected in 14.9
days of data from times when all three LIGO detectors were operating. We
interpret the result in terms of a frequentist upper limit on the rate of
gravitational wave bursts and use the limits on the rate to constrain the
parameter space (string tension, reconnection probability, and loop sizes) of
cosmic string models.Comment: 11 pages, 3 figures. Replaced with version submitted to PR
A Joint Search for Gravitational Wave Bursts with AURIGA and LIGO
The first simultaneous operation of the AURIGA detector and the LIGO
observatory was an opportunity to explore real data, joint analysis methods
between two very different types of gravitational wave detectors: resonant bars
and interferometers. This paper describes a coincident gravitational wave burst
search, where data from the LIGO interferometers are cross-correlated at the
time of AURIGA candidate events to identify coherent transients. The analysis
pipeline is tuned with two thresholds, on the signal-to-noise ratio of AURIGA
candidate events and on the significance of the cross-correlation test in LIGO.
The false alarm rate is estimated by introducing time shifts between data sets
and the network detection efficiency is measured with simulated signals with
power in the narrower AURIGA band. In the absence of a detection, we discuss
how to set an upper limit on the rate of gravitational waves and to interpret
it according to different source models. Due to the short amount of analyzed
data and to the high rate of non-Gaussian transients in the detectors noise at
the time, the relevance of this study is methodological: this was the first
joint search for gravitational wave bursts among detectors with such different
spectral sensitivity and the first opportunity for the resonant and
interferometric communities to unify languages and techniques in the pursuit of
their common goal.Comment: 18 pages, IOP, 12 EPS figure
Stacked Search for Gravitational Waves from the 2006 SGR 1900+14 Storm
We present the results of a LIGO search for short-duration gravitational
waves (GWs) associated with the 2006 March 29 SGR 1900+14 storm. A new search
method is used, "stacking'' the GW data around the times of individual
soft-gamma bursts in the storm to enhance sensitivity for models in which
multiple bursts are accompanied by GW emission. We assume that variation in the
time difference between burst electromagnetic emission and potential burst GW
emission is small relative to the GW signal duration, and we time-align GW
excess power time-frequency tilings containing individual burst triggers to
their corresponding electromagnetic emissions. We use two GW emission models in
our search: a fluence-weighted model and a flat (unweighted) model for the most
electromagnetically energetic bursts. We find no evidence of GWs associated
with either model. Model-dependent GW strain, isotropic GW emission energy
E_GW, and \gamma = E_GW / E_EM upper limits are estimated using a variety of
assumed waveforms. The stacking method allows us to set the most stringent
model-dependent limits on transient GW strain published to date. We find E_GW
upper limit estimates (at a nominal distance of 10 kpc) of between 2x10^45 erg
and 6x10^50 erg depending on waveform type. These limits are an order of
magnitude lower than upper limits published previously for this storm and
overlap with the range of electromagnetic energies emitted in SGR giant flares.Comment: 7 pages, 3 figure
All-sky LIGO Search for Periodic Gravitational Waves in the Early S5 Data
We report on an all-sky search with the LIGO detectors for periodic
gravitational waves in the frequency range 50--1100 Hz and with the frequency's
time derivative in the range -5.0E-9 Hz/s to zero. Data from the first eight
months of the fifth LIGO science run (S5) have been used in this search, which
is based on a semi-coherent method (PowerFlux) of summing strain power.
Observing no evidence of periodic gravitational radiation, we report 95%
confidence-level upper limits on radiation emitted by any unknown isolated
rotating neutron stars within the search range. Strain limits below 1.E-24 are
obtained over a 200-Hz band, and the sensitivity improvement over previous
searches increases the spatial volume sampled by an average factor of about 100
over the entire search band. For a neutron star with nominal equatorial
ellipticity of 1.0E-6, the search is sensitive to distances as great as 500
pc--a range that could encompass many undiscovered neutron stars, albeit only a
tiny fraction of which would likely be rotating fast enough to be accessible to
LIGO. This ellipticity is at the upper range thought to be sustainable by
conventional neutron stars and well below the maximum sustainable by a strange
quark star.Comment: 6 pages, 1 figur
Search for Gravitational Wave Bursts from Soft Gamma Repeaters
We present the results of a LIGO search for short-duration gravitational
waves (GWs) associated with Soft Gamma Repeater (SGR) bursts. This is the first
search sensitive to neutron star f-modes, usually considered the most efficient
GW emitting modes. We find no evidence of GWs associated with any SGR burst in
a sample consisting of the 27 Dec. 2004 giant flare from SGR 1806-20 and 190
lesser events from SGR 1806-20 and SGR 1900+14 which occurred during the first
year of LIGO's fifth science run. GW strain upper limits and model-dependent GW
emission energy upper limits are estimated for individual bursts using a
variety of simulated waveforms. The unprecedented sensitivity of the detectors
allows us to set the most stringent limits on transient GW amplitudes published
to date. We find upper limit estimates on the model-dependent isotropic GW
emission energies (at a nominal distance of 10 kpc) between 3x10^45 and 9x10^52
erg depending on waveform type, detector antenna factors and noise
characteristics at the time of the burst. These upper limits are within the
theoretically predicted range of some SGR models.Comment: 6 pages, 1 Postscript figur
Sensitivity to Gravitational Waves from Compact Binary Coalescences Achieved during LIGO's Fifth and Virgo's First Science Run
We summarize the sensitivity achieved by the LIGO and Virgo gravitational
wave detectors for compact binary coalescence (CBC) searches during LIGO's
fifth science run and Virgo's first science run. We present noise spectral
density curves for each of the four detectors that operated during these
science runs which are representative of the typical performance achieved by
the detectors for CBC searches. These spectra are intended for release to the
public as a summary of detector performance for CBC searches during these
science runs.Comment: 12 pages, 5 figure
Search for gravitational-wave bursts in LIGO data from the fourth science run
The fourth science run of the LIGO and GEO 600 gravitational-wave detectors,
carried out in early 2005, collected data with significantly lower noise than
previous science runs. We report on a search for short-duration
gravitational-wave bursts with arbitrary waveform in the 64-1600 Hz frequency
range appearing in all three LIGO interferometers. Signal consistency tests,
data quality cuts, and auxiliary-channel vetoes are applied to reduce the rate
of spurious triggers. No gravitational-wave signals are detected in 15.5 days
of live observation time; we set a frequentist upper limit of 0.15 per day (at
90% confidence level) on the rate of bursts with large enough amplitudes to be
detected reliably. The amplitude sensitivity of the search, characterized using
Monte Carlo simulations, is several times better than that of previous
searches. We also provide rough estimates of the distances at which
representative supernova and binary black hole merger signals could be detected
with 50% efficiency by this analysis.Comment: Corrected amplitude sensitivities (7% change on average); 30 pages,
submitted to Classical and Quantum Gravit
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