93 research outputs found
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
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
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
Search for gravitational-wave bursts in the first year of the fifth LIGO science run
We present the results obtained from an all-sky search for gravitational-wave
(GW) bursts in the 64-2000 Hz frequency range in data collected by the LIGO
detectors during the first year (November 2005 - November 2006) of their fifth
science run. The total analyzed livetime was 268.6 days. Multiple hierarchical
data analysis methods were invoked in this search. The overall sensitivity
expressed in terms of the root-sum-square (rss) strain amplitude h_{rss} for
gravitational-wave bursts with various morphologies was in the range of 6 times
10^{-22} Hz^{-1/2} to a few times 10^{-21} Hz^{-1/2}. No GW signals were
observed and a frequentist upper limit of 3.6 events per year on the rate of
strong GW bursts was placed at the 90% confidence level. As in our previous
searches, we also combined this rate limit with the detection efficiency for
selected waveform morphologies to obtain event rate versus strength exclusion
curves. In sensitivity, these exclusion curves are the most stringent to date.Comment: v3: various figure and text edits; submitted to PRD; 26 page
Search for High Frequency Gravitational Wave Bursts in the First Calendar Year of LIGO's Fifth Science Run
We present an all-sky search for gravitational waves in the frequency range 1
to 6 kHz during the first calendar year of LIGO's fifth science run. This is
the first untriggered LIGO burst analysis to be conducted above 3 kHz. We
discuss the unique properties of interferometric data in this regime. 161.3
days of triple-coincident data were analyzed. No gravitational events above
threshold were observed and a frequentist upper limit of 5.4 events per year on
the rate of strong gravitational wave bursts was placed at a 90% confidence
level. Implications for specific theoretical models of gravitational wave
emission are also discussed.Comment: 13 pages, accepted for publication in Physical Review
Search for gravitational wave ringdowns from perturbed black holes in LIGO S4 data
According to general relativity a perturbed black hole will settle to a
stationary configuration by the emission of gravitational radiation. Such a
perturbation will occur, for example, in the coalescence of a black hole
binary, following their inspiral and subsequent merger. At late times the
waveform is a superposition of quasi-normal modes, which we refer to as the
ringdown. The dominant mode is expected to be the fundamental mode, l=m=2.
Since this is a well-known waveform, matched filtering can be implemented to
search for this signal using LIGO data. We present a search for gravitational
waves from black hole ringdowns in the fourth LIGO science run S4, during which
LIGO was sensitive to the dominant mode of perturbed black holes with masses in
the range of 10 Msun to 500 Msun, the regime of intermediate-mass black holes,
to distances up to 300 Mpc. We present a search for gravitational waves from
black hole ringdowns using data from S4. No gravitational wave candidates were
found; we place a 90%-confidence upper limit on the rate of ringdowns from
black holes with mass between 85 Msun and 390 Msun in the local universe,
assuming a uniform distribution of sources, of 3.2 x 10^{-5} yr^{-1} Mpc^{-3} =
1.6 x 10^{-3}yr^{-1} L_{10}^{-1}, where L_{10} is 10^{10} times the solar
blue-light luminosity.Comment: 8 pages, 6 figure
Calibration of the LIGO gravitational wave detectors in the fifth science run
The Laser Interferometer Gravitational Wave Observatory (LIGO) is a network of three detectors built to detect local perturbations in the space–time metric from astrophysical sources. These detectors, two in Hanford, WA and one in Livingston, LA, are power-recycled Fabry-Perot Michelson interferometers. In their fifth science run (S5), between November 2005 and October 2007, these detectors accumulated one year of triple coincident data while operating at their designed sensitivity. In this paper, we describe the calibration of the instruments in the S5 data set, including measurement techniques and uncertainty estimation.United States. National Aeronautics and Space AdministrationCarnegie TrustLeverhulme TrustDavid & Lucile Packard FoundationResearch CorporationAlfred P. Sloan Foundatio
The present gravitational wave detection effort
Gravitational radiation offers a new non-electromagnetic window through which to observe the universe. The LIGO and Virgo Collaborations have completed a first joint data run with unprecedented sensitivities to gravitational waves. Results from searches in the data for a variety of astrophysical sources are presented. A second joint data run with improved detector sensitivities is underway, and soon major upgrades will be carried out to build Advanced LIGO and Advanced Virgo with expected improvements in event rates of more than 1000. In parallel there is a vigorous effort in the radio pulsar community to detect nHz gravitational waves via the timing residuals in an array of pulsars at different locations in the sky.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/85430/1/jpconf10_203_012002.pd
Pan-cancer analysis of whole genomes
Cancer is driven by genetic change, and the advent of massively parallel sequencing has enabled systematic documentation of this variation at the whole-genome scale(1-3). Here we report the integrative analysis of 2,658 whole-cancer genomes and their matching normal tissues across 38 tumour types from the Pan-Cancer Analysis of Whole Genomes (PCAWG) Consortium of the International Cancer Genome Consortium (ICGC) and The Cancer Genome Atlas (TCGA). We describe the generation of the PCAWG resource, facilitated by international data sharing using compute clouds. On average, cancer genomes contained 4-5 driver mutations when combining coding and non-coding genomic elements; however, in around 5% of cases no drivers were identified, suggesting that cancer driver discovery is not yet complete. Chromothripsis, in which many clustered structural variants arise in a single catastrophic event, is frequently an early event in tumour evolution; in acral melanoma, for example, these events precede most somatic point mutations and affect several cancer-associated genes simultaneously. Cancers with abnormal telomere maintenance often originate from tissues with low replicative activity and show several mechanisms of preventing telomere attrition to critical levels. Common and rare germline variants affect patterns of somatic mutation, including point mutations, structural variants and somatic retrotransposition. A collection of papers from the PCAWG Consortium describes non-coding mutations that drive cancer beyond those in the TERT promoter(4); identifies new signatures of mutational processes that cause base substitutions, small insertions and deletions and structural variation(5,6); analyses timings and patterns of tumour evolution(7); describes the diverse transcriptional consequences of somatic mutation on splicing, expression levels, fusion genes and promoter activity(8,9); and evaluates a range of more-specialized features of cancer genomes(8,10-18).Peer reviewe
Sex differences in oncogenic mutational processes
Sex differences have been observed in multiple facets of cancer epidemiology, treatment and biology, and in most cancers outside the sex organs. Efforts to link these clinical differences to specific molecular features have focused on somatic mutations within the coding regions of the genome. Here we report a pan-cancer analysis of sex differences in whole genomes of 1983 tumours of 28 subtypes as part of the ICGC/TCGA Pan-Cancer Analysis of Whole Genomes (PCAWG) Consortium. We both confirm the results of exome studies, and also uncover previously undescribed sex differences. These include sex-biases in coding and non-coding cancer drivers, mutation prevalence and strikingly, in mutational signatures related to underlying mutational processes. These results underline the pervasiveness of molecular sex differences and strengthen the call for increased consideration of sex in molecular cancer research
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