4,773 research outputs found
Searching for periodic sources with LIGO. II: Hierarchical searches
The detection of quasi-periodic sources of gravitational waves requires the
accumulation of signal-to-noise over long observation times. If not removed,
Earth-motion induced Doppler modulations, and intrinsic variations of the
gravitational-wave frequency make the signals impossible to detect. These
effects can be corrected (removed) using a parameterized model for the
frequency evolution. We compute the number of independent corrections
required for incoherent search strategies which use stacked
power spectra---a demodulated time series is divided into segments of
length , each segment is FFTed, the power is computed, and the
spectra are summed up. We estimate that the sensitivity of an all-sky search
that uses incoherent stacks is a factor of 2--4 better than would be achieved
using coherent Fourier transforms; incoherent methods are computationally
efficient at exploring large parameter spaces. A two-stage hierarchical search
which yields another 20--60% improvement in sensitivity in all-sky searches for
old (>= 1000 yr) slow (= 40 yr) fast (<=
1000 Hz) pulsars. Assuming 10^{12} flops of effective computing power for data
analysis, enhanced LIGO interferometers should be sensitive to: (i) Galactic
core pulsars with gravitational ellipticities of \epsilon\agt5\times 10^{-6}
at 200 Hz, (ii) Gravitational waves emitted by the unstable r-modes of newborn
neutron stars out to distances of ~8 Mpc, and (iii) neutron stars in LMXB's
with x-ray fluxes which exceed . Moreover,
gravitational waves from the neutron star in Sco X-1 should be detectable is
the interferometer is operated in a signal-recycled, narrow-band configuration.Comment: 22 Pages, 13 Figure
Gravitational waves: search results, data analysis and parameter estimation
The Amaldi 10 Parallel Session C2 on gravitational wave (GW) search results, data analysis and parameter estimation included three lively sessions of lectures by 13 presenters, and 34 posters. The talks and posters covered a huge range of material, including results and analysis techniques for ground-based GW detectors, targeting anticipated signals from different astrophysical sources: compact binary inspiral, merger and ringdown; GW bursts from intermediate mass binary black hole mergers, cosmic string cusps, core-collapse supernovae, and other unmodeled sources; continuous waves from spinning neutron stars; and a stochastic GW background. There was considerable emphasis on Bayesian techniques for estimating the parameters of coalescing compact binary systems from the gravitational waveforms extracted from the data from the advanced detector network. This included methods to distinguish deviations of the signals from what is expected in the context of General Relativity
Implementation of the frequency-modulated sideband search method for gravitational waves from low mass X-ray binaries
We describe the practical implementation of the sideband search, a search for
periodic gravitational waves from neutron stars in binary systems. The orbital
motion of the source in its binary system causes frequency-modulation in the
combination of matched filters known as the -statistic. The
sideband search is based on the incoherent summation of these
frequency-modulated -statistic sidebands. It provides a new
detection statistic for sources in binary systems, called the
-statistic. The search is well suited to low-mass X-ray binaries,
the brightest of which, called Sco X-1, is an ideal target candidate. For
sources like Sco X-1, with well constrained orbital parameters, a slight
variation on the search is possible. The extra orbital information can be used
to approximately demodulate the data from the binary orbital motion in the
coherent stage, before incoherently summing the now reduced number of
sidebands. We investigate this approach and show that it improves the
sensitivity of the standard Sco X-1 directed sideband search. Prior information
on the neutron star inclination and gravitational wave polarization can also be
used to improve upper limit sensitivity. We estimate the sensitivity of a Sco
X-1 directed sideband search on 10 days of LIGO data and show that it can beat
previous upper limits in current LIGO data, with a possibility of constraining
theoretical upper limits using future advanced instruments.Comment: 20 pages, 5 figure
End-to-end algorithm for hierarchical area searches for long-duration GW sources for GEO 600
We describe a hierarchical, highly parallel computer algorithm to perform
searches for unknown sources of continuous gravitational waves -- spinning
neutron stars in the Galaxy -- over wide areas of the sky and wide frequency
bandwidths. We optimize the algorithm for an observing period of 4 months and
an available computing power of 20 Gflops, in a search for neutron stars
resembling millisecond pulsars. We show that, if we restrict the search to the
galactic plane, the method will detect any star whose signal is stronger than
15 times the noise level of a detector over that search period. Since
on grounds of confidence the minimum identifiable signal should be about 10
times noise, our algorithm does only 50% worse than this and runs on a computer
with achievable processing speed.Comment: 7 pages, for proceedings of Jan 1999 Moriond meeting "Gravitational
Waves and Experimental Gravity
A new data analysis framework for the search of continuous gravitational wave signals
Continuous gravitational wave signals, like those expected by asymmetric
spinning neutron stars, are among the most promising targets for LIGO and Virgo
detectors. The development of fast and robust data analysis methods is crucial
to increase the chances of a detection. We have developed a new and flexible
general data analysis framework for the search of this kind of signals, which
allows to reduce the computational cost of the analysis by about two orders of
magnitude with respect to current procedures. This can correspond, at fixed
computing cost, to a sensitivity gain of up to 10%-20%, depending on the search
parameter space. Some possible applications are discussed, with a particular
focus on a directed search for sources in the Galactic center. Validation
through the injection of artificial signals in the data of Advanced LIGO first
observational science run is also shown.Comment: 21 pages, 8 figure
Searching for continuous gravitational wave signals: the hierarchical Hough transform algorithm
It is well known that matched filtering techniques cannot be applied for
searching extensive parameter space volumes for continuous gravitational wave
signals. This is the reason why alternative strategies are being pursued.
Hierarchical strategies are best at investigating a large parameter space when
there exist computational power constraints. Algorithms of this kind are being
implemented by all the groups that are developing software for analyzing the
data of the gravitational wave detectors that will come online in the next
years. In this talk we will report about the hierarchical Hough transform
method that the GEO 600 data analysis team at the Albert Einstein Institute is
developing. The three step hierarchical algorithm has been described elsewhere.
In this talk we will focus on some of the implementational aspects we are
currently concerned with.Comment: 9 pages, 1 figure. To appear in the proceedings of the conference
``Gravitational waves: a challenge to theoretical astrophysics'', (June 5-9
2000, Trieste), ICTP Lecture Notes Serie
Resampling to accelerate cross-correlation searches for continuous gravitational waves from binary systems
Continuous-wave (CW) gravitational waves (GWs) call for
computationally-intensive methods. Low signal-to-noise ratio signals need
templated searches with long coherent integration times and thus fine
parameter-space resolution. Longer integration increases sensitivity. Low-mass
x-ray binaries (LMXBs) such as Scorpius X-1 (Sco X-1) may emit accretion-driven
CWs at strains reachable by current ground-based observatories. Binary orbital
parameters induce phase modulation. This paper describes how resampling
corrects binary and detector motion, yielding source-frame time series used for
cross-correlation. Compared to the previous, detector-frame, templated
cross-correlation method, used for Sco X-1 on data from the first Advanced LIGO
observing run (O1), resampling is about 20x faster in the costliest,
most-sensitive frequency bands. Speed-up factors depend on integration time and
search setup. The speed could be reinvested into longer integration with a
forecast sensitivity gain, 20 to 125 Hz median, of approximately 51%, or from
20 to 250 Hz, 11%, given the same per-band cost and setup. This paper's timing
model enables future setup optimization. Resampling scales well with longer
integration, and at 10x unoptimized cost could reach respectively 2.83x and
2.75x median sensitivities, limited by spin-wandering. Then an O1 search could
yield a marginalized-polarization upper limit reaching torque-balance at 100
Hz. Frequencies from 40 to 140 Hz might be probed in equal observing time with
2x improved detectors.Comment: 28 pages, 7 figures, 3 table
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