1,190 research outputs found
An all-sky search algorithm for continuous gravitational waves from spinning neutron stars in binary systems
Rapidly spinning neutron stars with non-axisymmetric mass distributions are
expected to generate quasi-monochromatic continuous gravitational waves. While
many searches for unknown, isolated spinning neutron stars have been carried
out, there have been no previous searches for unknown sources in binary
systems. Since current search methods for unknown, isolated neutron stars are
already computationally limited, expanding the parameter space searched to
include binary systems is a formidable challenge. We present a new hierarchical
binary search method called TwoSpect, which exploits the periodic orbital
modulations of the continuous waves by searching for patterns in doubly
Fourier-transformed data. We will describe the TwoSpect search pipeline,
including its mitigation of detector noise variations and corrections for
Doppler frequency modulation caused by changing detector velocity. Tests on
Gaussian noise and on a set of simulated signals will be presented.Comment: 22 pages, 10 figures, 1 table, Submitted to Classical and Quantum
Gravit
A blind hierarchical coherent search for gravitational-wave signals from coalescing compact binaries in a network of interferometric detectors
We describe a hierarchical data analysis pipeline for coherently searching
for gravitational wave (GW) signals from non-spinning compact binary
coalescences (CBCs) in the data of multiple earth-based detectors. It assumes
no prior information on the sky position of the source or the time of
occurrence of its transient signals and, hence, is termed "blind". The pipeline
computes the coherent network search statistic that is optimal in stationary,
Gaussian noise, and allows for the computation of a suite of alternative
statistics and signal-based discriminators that can improve its performance in
real data. Unlike the coincident multi-detector search statistics employed so
far, the coherent statistics are different in the sense that they check for the
consistency of the signal amplitudes and phases in the different detectors with
their different orientations and with the signal arrival times in them. The
first stage of the hierarchical pipeline constructs coincidences of triggers
from the multiple interferometers, by requiring their proximity in time and
component masses. The second stage follows up on these coincident triggers by
computing the coherent statistics. The performance of the hierarchical coherent
pipeline on Gaussian data is shown to be better than the pipeline with just the
first (coincidence) stage.Comment: 12 pages, 3 figures, accepted for publication in Classical and
Quantum Gravit
Enhancing gravitational wave astronomy with galaxy catalogues
Joint gravitational wave (GW) and electromagnetic (EM) observations, as a key
research direction in multi-messenger astronomy, will provide deep insight into
the astrophysics of a vast range of astronomical phenomena. Uncertainties in
the source sky location estimate from gravitational wave observations mean
follow-up observatories must scan large portions of the sky for a potential
companion signal. A general frame of joint GW-EM observations is presented by a
multi-messenger observational triangle. Using a Bayesian approach to
multi-messenger astronomy, we investigate the use of galaxy catalogue and host
galaxy information to reduce the sky region over which follow-up observatories
must scan, as well as study its use for improving the inclination angle
estimates for coalescing binary compact objects. We demonstrate our method
using a simulated neutron stars inspiral signal injected into simulated
Advanced detectors noise and estimate the injected signal sky location and
inclination angle using the Gravitational Wave Galaxy Catalogue. In this case
study, the top three candidates in rank have , and posterior
probability of being the host galaxy, receptively. The standard deviation of
cosine inclination angle (0.001) of the neutron stars binary using
gravitational wave-galaxy information is much smaller than that (0.02) using
only gravitational wave posterior samples.Comment: Proceedings of the Sant Cugat Forum on Astrophysics. 2014 Session on
'Gravitational Wave Astrophysics
A "kilonova" associated with short-duration gamma-ray burst 130603B
Short-duration gamma-ray bursts (SGRBs) are intense flashes of cosmic
gamma-rays, lasting less than ~2 s, whose origin is one of the great unsolved
questions of astrophysics today. While the favoured hypothesis for their
production, a relativistic jet created by the merger of two compact stellar
objects (specifically, two neutron stars, NS-NS, or a neutron star and a black
hole, NS-BH), is supported by indirect evidence such as their host galaxy
properties, unambiguous confirmation of the model is still lacking. Mergers of
this kind are also expected to create significant quantities of neutron-rich
radioactive species, whose decay should result in a faint transient in the days
following the burst, a so-called "kilonova". Indeed, it is speculated that this
mechanism may be the predominant source of stable r-process elements in the
Universe. Recent calculations suggest much of the kilonova energy should appear
in the near-infrared (nIR) due to the high optical opacity created by these
heavy r-process elements. Here we report strong evidence for such an event
accompanying SGRB 130603B. If this simplest interpretation of the data is
correct, it provides (i) support for the compact object merger hypothesis of
SGRBs, (ii) confirmation that such mergers are likely sites of significant
r-process production and (iii) quite possibly an alternative, un-beamed
electromagnetic signature of the most promising sources for direct detection of
gravitational waves.Comment: preprint of paper appearing in Nature (3 Aug 2013
A coherent triggered search for single spin compact binary coalescences in gravitational wave data
In this paper we present a method for conducting a coherent search for single
spin compact binary coalescences in gravitational wave data and compare this
search to the existing coincidence method for single spin searches. We propose
a method to characterize the regions of the parameter space where the single
spin search, both coincident and coherent, will increase detection efficiency
over the existing non-precessing search. We also show example results of the
coherent search on a stretch of data from LIGO's fourth science run but note
that a set of signal based vetoes will be needed before this search can be run
to try to make detections.Comment: 14 pages, 4 figure
The Critical Coupling Likelihood Method: A new approach for seamless integration of environmental and operating conditions of gravitational wave detectors into gravitational wave searches
Any search effort for gravitational waves (GW) using interferometric
detectors like LIGO needs to be able to identify if and when noise is coupling
into the detector's output signal. The Critical Coupling Likelihood (CCL)
method has been developed to characterize potential noise coupling and in the
future aid GW search efforts. By testing two hypotheses about pairs of
channels, CCL is able to identify undesirable coupled instrumental noise from
potential GW candidates. Our preliminary results show that CCL can associate up
to of observed artifacts with , to local noise sources,
while reducing the duty cycle of the instrument by . An approach
like CCL will become increasingly important as GW research moves into the
Advanced LIGO era, going from the first GW detection to GW astronomy.Comment: submitted CQ
Crew Exploration Vehicle Ascent Abort Coverage Analysis
An important element in the design of NASA's Crew Exploration Vehicle (CEV) is the consideration given to crew safety during various ascent phase failure scenarios. To help ensure crew safety during this critical and dynamic flight phase, the CEV requirements specify that an abort capability must be continuously available from lift-off through orbit insertion. To address this requirement, various CEV ascent abort modes are analyzed using 3-DOF (Degree Of Freedom) and 6-DOF simulations. The analysis involves an evaluation of the feasibility and survivability of each abort mode and an assessment of the abort mode coverage using the current baseline vehicle design. Factors such as abort system performance, crew load limits, thermal environments, crew recovery, and vehicle element disposal are investigated to determine if the current vehicle requirements are appropriate and achievable. Sensitivity studies and design trades are also completed so that more informed decisions can be made regarding the vehicle design. An overview of the CEV ascent abort modes is presented along with the driving requirements for abort scenarios. The results of the analysis completed as part of the requirements validation process are then discussed. Finally, the conclusions of the study are presented, and future analysis tasks are recommended
A tapering window for time-domain templates and simulated signals in the detection of gravitational waves from coalescing compact binaries
Inspiral signals from binary black holes, in particular those with masses in
the range 10M_\odot \lsim M \lsim 1000 M_\odot, may last for only a few
cycles within a detector's most sensitive frequency band. The spectrum of a
square-windowed time-domain signal could contain unwanted power that can cause
problems in gravitational wave data analysis, particularly when the waveforms
are of short duration. There may be leakage of power into frequency bins where
no such power is expected, causing an excess of false alarms. We present a
method of tapering the time-domain waveforms that significantly reduces
unwanted leakage of power, leading to a spectrum that agrees very well with
that of a long duration signal. Our tapered window also decreases the false
alarms caused by instrumental and environmental transients that are picked up
by templates with spurious signal power. The suppression of background is an
important goal in noise-dominated searches and can lead to an improvement in
the detection efficiency of the search algorithms
The next detectors for gravitational wave astronomy
This paper focuses on the next detectors for gravitational wave astronomy
which will be required after the current ground based detectors have completed
their initial observations, and probably achieved the first direct detection of
gravitational waves. The next detectors will need to have greater sensitivity,
while also enabling the world array of detectors to have improved angular
resolution to allow localisation of signal sources. Sect. 1 of this paper
begins by reviewing proposals for the next ground based detectors, and presents
an analysis of the sensitivity of an 8 km armlength detector, which is proposed
as a safe and cost-effective means to attain a 4-fold improvement in
sensitivity. The scientific benefits of creating a pair of such detectors in
China and Australia is emphasised. Sect. 2 of this paper discusses the high
performance suspension systems for test masses that will be an essential
component for future detectors, while sect. 3 discusses solutions to the
problem of Newtonian noise which arise from fluctuations in gravity gradient
forces acting on test masses. Such gravitational perturbations cannot be
shielded, and set limits to low frequency sensitivity unless measured and
suppressed. Sects. 4 and 5 address critical operational technologies that will
be ongoing issues in future detectors. Sect. 4 addresses the design of thermal
compensation systems needed in all high optical power interferometers operating
at room temperature. Parametric instability control is addressed in sect. 5.
Only recently proven to occur in Advanced LIGO, parametric instability
phenomenon brings both risks and opportunities for future detectors. The path
to future enhancements of detectors will come from quantum measurement
technologies. Sect. 6 focuses on the use of optomechanical devices for
obtaining enhanced sensitivity, while sect. 7 reviews a range of quantum
measurement options
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