1,298 research outputs found
Thermo-optic noise in coated mirrors for high-precision optical measurements
Thermal fluctuations in the coatings used to make high-reflectors are
becoming significant noise sources in precision optical measurements and are
particularly relevant to advanced gravitational wave detectors. There are two
recognized sources of coating thermal noise, mechanical loss and thermal
dissipation. Thermal dissipation causes thermal fluctuations in the coating
which produce noise via the thermo-elastic and thermo-refractive mechanisms. We
treat these mechanisms coherently, give a correction for finite coating
thickness, and evaluate the implications for Advanced LIGO
A fast search strategy for gravitational waves from low-mass X-ray binaries
We present a new type of search strategy designed specifically to find
continuously emitting gravitational wave sources in known binary systems based
on the incoherent sum of frequency modulated binary signal sidebands. The
search pipeline can be divided into three stages: the first is a wide
bandwidth, F-statistic search demodulated for sky position. This is followed by
a fast second stage in which areas in frequency space are identified as signal
candidates through the frequency domain convolution of the F-statistic with an
approximate signal template. For this second stage only precise information on
the orbit period and approximate information on the orbital semi-major axis are
required apriori. For the final stage we propose a fully coherent Markov chain
monte carlo based follow up search on the frequency subspace defined by the
candidates identified by the second stage. This search is particularly suited
to the low-mass X-ray binaries, for which orbital period and sky position are
typically well known and additional orbital parameters and neutron star spin
frequency are not. We note that for the accreting X-ray millisecond pulsars,
for which spin frequency and orbital parameters are well known, the second
stage can be omitted and the fully coherent search stage can be performed. We
describe the search pipeline with respect to its application to a simplified
phase model and derive the corresponding sensitivity of the search.Comment: 13 pages, 3 figures, to appear in the GWDAW 11 conference proceeding
Evidence of Volatile-Induced Melting in the Northeast Asian Upper Mantle
A seismic low velocity layer (LVL) above the mantle transition zone (MTZ), often thought to be caused by volatile-induced melting, can significantly modulate planetary volatile cycles. In this work, we show that an LVL observed beneath northeast Asia is characterized by small, 0.8 (Formula presented.) 0.5 vol%, average degrees of partial melting. Seismically derived P-T conditions of the LVL indicate that slab-derived (Formula presented.), possibly combined with small amounts of (Formula presented.) O, is necessary to induce melting. Modeling the reactive infiltration instability of the melt in a stationary mantle above a stalled slab, we demonstrate that the volatile-rich melt slowly rises above the stalled slab in the MTZ, with percolation velocities of 200–500 (Formula presented.) m/yr. The melt remains stable within the LVL for this geologically significant period of time, potentially transferring up to 52 Mt/yr of (Formula presented.) from the subducting slab to the mantle for an LVL similar in areal extent ((Formula presented.)) to the northeast Asian LVL. Reaction between the melt channels and the LVL mantle precipitates up to 200 ppmw solid C in localized zones. Using the inferred small melt volume fraction to model trace element abundances and isotopic signatures, we show that interaction between this melt and the surrounding mantle can over the long-term produce rocks bearing a HIMU like geochemical signature
Search for gravitational waves associated with the August 2006 timing glitch of the Vela pulsar
The physical mechanisms responsible for pulsar timing glitches are thought to excite quasinormal mode oscillations in their parent neutron star that couple to gravitational-wave emission. In August 2006, a timing glitch was observed in the radio emission of PSR B0833-45, the Vela pulsar. At the time of the glitch, the two colocated Hanford gravitational-wave detectors of the Laser Interferometer Gravitational wave observatory (LIGO) were operational and taking data as part of the fifth LIGO science run (S5). We present the first direct search for the gravitational-wave emission associated with oscillations of the fundamental quadrupole mode excited by a pulsar timing glitch. No gravitational-wave detection
candidate was found. We place Bayesian 90% confidence upper limits of 6.3 x 10^(-21) to 1.4 x 10^(-20) on the peak intrinsic strain amplitude of gravitational-wave ring-down signals, depending on which spherical harmonic mode is excited. The corresponding range of energy upper limits is 5.0 x 10^(-44) to 1.3 x 10^(-45) erg
Science-Driven Tunable Design of Cosmic Explorer Detectors
Ground-based gravitational-wave detectors like Cosmic Explorer can be tuned
to improve their sensitivity at high or low frequencies by tuning the response
of the signal extraction cavity. Enhanced sensitivity above 2 kHz enables
measurements of the post-merger gravitational-wave spectrum from binary neutron
star mergers, which depends critically on the unknown equation of state of hot,
ultra-dense matter. Improved sensitivity below 500 Hz favors precision tests of
extreme gravity with black hole ringdown signals and improves the detection
prospects while facilitating an improved measurement of source properties for
compact binary inspirals at cosmological distances. At intermediate
frequencies, a more sensitive detector can better measure the tidal properties
of neutron stars. We present and characterize the performance of tuned Cosmic
Explorer configurations that are designed to optimize detections across
different astrophysical source populations. These tuning options give Cosmic
Explorer the flexibility to target a diverse set of science goals with the same
detector infrastructure. We find that a 40 km Cosmic Explorer detector
outperforms a 20 km in all key science goals other than access to post-merger
physics. This suggests that Cosmic Explorer should include at least one 40 km
facility
Feasibility of measuring the Shapiro time delay over meter-scale distances
The time delay of light as it passes by a massive object, first calculated by
Shapiro in 1964, is a hallmark of the curvature of space-time. To date, all
measurements of the Shapiro time delay have been made over solar-system
distance scales. We show that the new generation of kilometer-scale laser
interferometers being constructed as gravitational wave detectors, in
particular Advanced LIGO, will in principle be sensitive enough to measure
variations in the Shapiro time delay produced by a suitably designed rotating
object placed near the laser beam. We show that such an apparatus is feasible
(though not easy) to construct, present an example design, and calculate the
signal that would be detectable by Advanced LIGO. This offers the first
opportunity to measure space-time curvature effects on a laboratory distance
scale.Comment: 13 pages, 6 figures; v3 has updated instrumental noise curves plus a
few text edits; resubmitted to Classical and Quantum Gravit
Gravitational wave radiometry: Mapping a stochastic gravitational wave background
The problem of the detection and mapping of a stochastic gravitational wave
background (SGWB), either of cosmological or astrophysical origin, bears a
strong semblance to the analysis of CMB anisotropy and polarization. The basic
statistic we use is the cross-correlation between the data from a pair of
detectors. In order to `point' the pair of detectors at different locations one
must suitably delay the signal by the amount it takes for the gravitational
waves (GW) to travel to both detectors corresponding to a source direction.
Then the raw (observed) sky map of the SGWB is the signal convolved with a beam
response function that varies with location in the sky. We first present a
thorough analytic understanding of the structure of the beam response function
using an analytic approach employing the stationary phase approximation. The
true sky map is obtained by numerically deconvolving the beam function in the
integral (convolution) equation. We adopt the maximum likelihood framework to
estimate the true sky map that has been successfully used in the broadly
similar, well-studied CMB map making problem. We numerically implement and
demonstrate the method on simulated (unpolarized) SGWB for the radiometer
consisting of the LIGO pair of detectors at Hanford and Livingston. We include
`realistic' additive Gaussian noise in each data stream based on the LIGO-I
noise power spectral density. The extension of the method to multiple baselines
and polarized GWB is outlined. In the near future the network of GW detectors,
including the Advanced LIGO and Virgo detectors that will be sensitive to
sources within a thousand times larger spatial volume, could provide promising
data sets for GW radiometry.Comment: 24 pages, 19 figures, pdflatex. Matched version published in Phys.
Rev. D - minor change
The path to the enhanced and advanced LIGO gravitational-wave detectors
We report on the status of the Laser Interferometric Gravitational-Wave
Observatory (LIGO) and the plans and progress towards Enhanced and Advanced
LIGO. The initial LIGO detectors have finished a two year long data run during
which a full year of triple-coincidence data was collected at design
sensitivity. Much of this run was also coincident with the data runs of
interferometers in Europe, GEO600 and Virgo. The joint analysis of data from
this international network of detectors is ongoing. No gravitational wave
signals have been detected in analyses completed to date. Currently two of the
LIGO detectors are being upgraded to increase their sensitivity in a program
called Enhanced LIGO. The Enhanced LIGO detectors will start another roughly
one year long data run with increased sensitivity in 2009. In parallel,
construction of Advanced LIGO, a major upgrade to LIGO, has begun. Installation
and commissioning of Advanced LIGO hardware at the LIGO sites will commence at
the end of the Enhanced LIGO data run in 2011. When fully commissioned, the
Advanced LIGO detectors will be ten times as sensitive as the initial LIGO
detectors. Advanced LIGO is expected to make several gravitational wave
detections per year.Comment: 11 pages, 5 figure
Progress towards Gravitational Wave Astronomy
I will review the most recent and interesting results from gravitational wave
detection experiments, concentrating on recent results from the LIGO Scientific
Collaboration (LSC). I will outline the methodologies utilized in the searches,
explain what can be said in the case of a null result, what quantities may be
constrained. I will compare these results with prior expectations and discuss
their significance. As I go along I will outline the prospects for future
improvements.Comment: Based on a talk presented at the joint "18th International Conference
on General Relativity and Gravitation" and "7th Amaldi Conference on
Gravitational Waves", 8-13 July 2007, Sydney, Australi
Implications for the origin of GRB 051103 from LIGO observations
We present the results of a LIGO search for gravitational waves (GWs) associated with GRB 051103, a short-duration hard-spectrum gamma-ray burst (GRB) whose electromagnetically determined sky position is coincident with the spiral galaxy M81, which is 3.6Mpc from Earth. Possible progenitors for short-hard GRBs include compact object mergers and soft gamma repeater (SGR) giant flares. A merger progenitor would produce a characteristic GW signal that should be detectable at a distance of M81, while GW emission from an SGR is not expected to be detectable at that distance. We found no evidence of a GW signal associated with GRB 051103. Assuming weakly beamed γ-ray emission with a jet semi-angle of 30°, we exclude a binary neutron star merger in M81 as the progenitor with a confidence of 98%. Neutron star-black hole mergers are excluded with \u3e99% confidence. If the event occurred in M81, then our findings support the hypothesis that GRB 051103 was due to an SGR giant flare, making it one of the most distant extragalactic magnetars observed to date. © 2012 The American Astronomical Society. All rights reserved
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