2,094 research outputs found
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 and localization of continuous gravitational waves with pulsar timing arrays: the role of pulsar terms
A pulsar timing array is a Galactic-scale detector of nanohertz gravitational
waves (GWs). Its target signals contain two components: the `Earth term' and
the `pulsar term' corresponding to GWs incident on the Earth and pulsar
respectively. In this work we present a Frequentist method for the detection
and localization of continuous waves that takes into account the pulsar term
and is significantly faster than existing methods. We investigate the role of
pulsar terms by comparing a full-signal search with an Earth-term-only search
for non-evolving black hole binaries. By applying the method to synthetic data
sets, we find that (i) a full-signal search can slightly improve the detection
probability (by about five percent); (ii) sky localization is biased if only
Earth terms are searched for and the inclusion of pulsar terms is critical to
remove such a bias; (iii) in the case of strong detections (with
signal-to-noise ratio 30), it may be possible to improve pulsar
distance estimation through GW measurements.Comment: 12 pages, 9 figures, typos corrected. To match the published version.
Code implementing this method is available at the PPTA Wiki pag
Gravitational waves from Sco X-1: A comparison of search methods and prospects for detection with advanced detectors
The low-mass X-ray binary Scorpius X-1 (Sco X-1) is potentially the most
luminous source of continuous gravitational-wave radiation for interferometers
such as LIGO and Virgo. For low-mass X-ray binaries this radiation would be
sustained by active accretion of matter from its binary companion. With the
Advanced Detector Era fast approaching, work is underway to develop an array of
robust tools for maximizing the science and detection potential of Sco X-1. We
describe the plans and progress of a project designed to compare the numerous
independent search algorithms currently available. We employ a mock-data
challenge in which the search pipelines are tested for their relative
proficiencies in parameter estimation, computational efficiency, robust- ness,
and most importantly, search sensitivity. The mock-data challenge data contains
an ensemble of 50 Scorpius X-1 (Sco X-1) type signals, simulated within a
frequency band of 50-1500 Hz. Simulated detector noise was generated assuming
the expected best strain sensitivity of Advanced LIGO and Advanced VIRGO ( Hz). A distribution of signal amplitudes was then
chosen so as to allow a useful comparison of search methodologies. A factor of
2 in strain separates the quietest detected signal, at
strain, from the torque-balance limit at a spin frequency of 300 Hz, although
this limit could range from (25 Hz) to (750 Hz) depending on the unknown frequency of Sco X-1. With future
improvements to the search algorithms and using advanced detector data, our
expectations for probing below the theoretical torque-balance strain limit are
optimistic.Comment: 33 pages, 11 figure
Practical Methods for Continuous Gravitational Wave Detection using Pulsar Timing Data
Gravitational Waves (GWs) are tiny ripples in the fabric of space-time
predicted by Einstein's General Relativity. Pulsar timing arrays (PTAs) are
well poised to detect low frequency ( -- Hz) GWs in the near
future. There has been a significant amount of research into the detection of a
stochastic background of GWs from supermassive black hole binaries (SMBHBs).
Recent work has shown that single continuous sources standing out above the
background may be detectable by PTAs operating at a sensitivity sufficient to
detect the stochastic background. The most likely sources of continuous GWs in
the pulsar timing frequency band are extremely massive and/or nearby SMBHBs. In
this paper we present detection strategies including various forms of matched
filtering and power spectral summing. We determine the efficacy and
computational cost of such strategies. It is shown that it is computationally
infeasible to use an optimal matched filter including the poorly constrained
pulsar distances with a grid based method. We show that an Earth-term-matched
filter constructed using only the correlated signal terms is both
computationally viable and highly sensitive to GW signals. This technique is
only a factor of two less sensitive than the computationally unrealizable
optimal matched filter and a factor of two more sensitive than a power spectral
summing technique. We further show that a pairwise matched filter, taking the
pulsar distances into account is comparable to the optimal matched filter for
the single template case and comparable to the Earth-term-matched filter for
many search templates. Finally, using simulated data optimal quality, we place
a theoretical minimum detectable strain amplitude of from
continuous GWs at frequencies on the order .Comment: submitted to Ap
Setting upper limits on the strength of periodic gravitational waves from PSR J1939+2134 using the first science data from the GEO 600 and LIGO detectors
Data collected by the GEO 600 and LIGO interferometric gravitational wave detectors during their first observational science run were searched for continuous gravitational waves from the pulsar J1939+2134 at twice its rotation frequency. Two independent analysis methods were used and are demonstrated in this paper: a frequency domain method and a time domain method. Both achieve consistent null results, placing new upper limits on the strength of the pulsar's gravitational wave emission. A model emission mechanism is used to interpret the limits as a constraint on the pulsar's equatorial ellipticity
Parameter-space metric for all-sky semicoherent searches for gravitational-wave pulsars
The sensitivity of all-sky searches for gravitational-wave pulsars is
primarily limited by the finite availability of computing resources.
Semicoherent searches are a widely-used method of maximizing sensitivity to
gravitational-wave pulsars at fixed computing cost: the data from a
gravitational-wave detector are partitioned into a number of segments, each
segment is coherently analyzed, and the analysis results from each segment are
summed together. The generation of template banks for the coherent analysis of
each segment, and for the summation, requires knowledge of the metrics
associated with the coherent and semicoherent parameter spaces respectively. We
present a useful approximation to the semicoherent parameter-space metric,
analogous to that presented in Wette and Prix [Phys. Rev. D 88, 123005 (2013)]
for the coherent metric. The new semicoherent metric is compared to previous
work in Pletsch [Phys. Rev. D 82, 042002 (2010)], and Brady and Creighton
[Phys. Rev. D 61, 082001 (2000)]. We find that semicoherent all-sky searches
require orders of magnitude more templates than previously predicted.Comment: 21 pages, 13 figures, 2 table
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