925 research outputs found
Using generalized PowerFlux methods to estimate the parameters of periodic gravitational waves
We investigate methods to estimate the parameters of the gravitational-wave
signal from a spinning neutron star using Fourier transformed segments of the
strain response from an interferometric detector. Estimating the parameters
from the power, we find generalizations of the PowerFlux method. Using
simulated elliptically polarized signals injected into Gaussian noise, we apply
the generalized methods to estimate the squared amplitudes of the plus and
cross polarizations (and, in the most general case, the polarization angle),
and test the relative detection efficiencies of the various methods.Comment: 8 pages, presented at Amalid7, Sydney, Australia (July 2007), fixed
minor typos and clarified discussion to match published CQG version; updated
reference
Design optimization of the JPL Phase B testbed
Increasingly complex spacecraft will benefit from integrated design and optimization of structural, optical, and control subsystems. Integrated design optimization will allow designers to make tradeoffs in objectives and constraints across these subsystems. The location, number, and types of passive and active devices distributed along the structure can have a dramatic impact on overall system performance. In addition, the manner in which structural mass is distributed can also serve as an effective mechanism for attenuating disturbance transmission between source and sensitive system components. This paper presents recent experience using optimization tools that have been developed for addressing some of these issues on a challenging testbed design problem. This particular testbed is one of a series of testbeds at the Jet Propulsion Laboratory under the sponsorship of the NASA Control Structure Interaction (CSI) Program to demonstrate nanometer level optical pathlength control on a flexible truss structure that emulates a spaceborne interferometer
Proceedings of the Fifth NASA/NSF/DOD Workshop on Aerospace Computational Control
The Fifth Annual Workshop on Aerospace Computational Control was one in a series of workshops sponsored by NASA, NSF, and the DOD. The purpose of these workshops is to address computational issues in the analysis, design, and testing of flexible multibody control systems for aerospace applications. The intention in holding these workshops is to bring together users, researchers, and developers of computational tools in aerospace systems (spacecraft, space robotics, aerospace transportation vehicles, etc.) for the purpose of exchanging ideas on the state of the art in computational tools and techniques
Inferring neutron star properties with continuous gravitational waves
Detection of continuous gravitational waves from rapidly-spinning neutron
stars opens up the possibility of examining their internal physics. We develop
a framework that leverages a future continuous gravitational wave detection to
infer a neutron star's moment of inertia, equatorial ellipticity, and the
component of the magnetic dipole moment perpendicular to its rotation axis. We
assume that the neutron star loses rotational kinetic energy through both
gravitational wave and electromagnetic radiation, and that the distance to the
neutron star can be measured, but do not assume electromagnetic pulsations are
observable or a particular neutron star equation of state. We use the Fisher
information matrix and Monte Carlo simulations to estimate errors in the
inferred parameters, assuming a population of gravitational-wave-emitting
neutron stars consistent with the typical parameter domains of continuous
gravitational wave searches. After an observation time of one year, the
inferred errors for many neutron stars are limited chiefly by the error in the
distance to the star. The techniques developed here will be useful if
continuous gravitational waves are detected from a radio, X-ray, or gamma-ray
pulsar, or else from a compact object with known distance, such as a supernova
remnant.Comment: 10 pages, 4 figures. To be published in MNRA
Population synthesis and parameter estimation of neutron stars with continuous gravitational waves and third-generation detectors
Precise measurement of stellar properties through the observation of
continuous gravitational waves from spinning non-axisymmetric neutron stars can
shed light onto new physics beyond terrestrial laboratories. Although hitherto
undetected, prospects for detecting continuous gravitational waves improve with
longer observation periods and more sensitive gravitational wave detectors. We
study the capability of the Advanced Laser Interferometer Gravitational-Wave
Observatory, and the Einstein Telescope to measure the physical properties of
neutron stars through continuous gravitational wave observations. We simulate a
population of Galactic neutron stars, assume continuous gravitational waves
from the stars have been detected, and perform parameter estimation of the
detected signals. Using the estimated parameters, we infer the stars' moments
of inertia, ellipticities, and the components of the magnetic dipole moment
perpendicular to the rotation axis. The estimation of the braking index proved
challenging and is responsible for the majority of the uncertainties in the
inferred parameters. Using the Einstein Telescope with an observation period of
5 yrs, point estimates using median can be made with errors of ~ 10 - 100% and
~ 5 - 50% respectively, subject to the inference of the braking index. The
perpendicular magnetic dipole moment could not be accurately inferred for
neutron stars that emit mainly gravitational waves.Comment: 11 pages, 7 figure
Valency of rare earths in RIn3 and RSn3: Ab initio analysis of electric-field gradients
In RIn3 and RSn3 the rare earth (R) is trivalent, except for Eu and Yb, which
are divalent. This was experimentally determined in 1977 by perturbed angular
correlation measurements of the electric-field gradient on a 111Cd impurity. At
that time, the data were interpreted using a point charge model, which is now
known to be unphysical and unreliable. This makes the valency determination
potentially questionable. We revisit these data, and analyze them using ab
initio calculations of the electric-field gradient. From these calculations,
the physical mechanism that is responsible for the influence of the valency on
the electric-field gradient is derived. A generally applicable scheme to
interpret electric-field gradients is used, which in a transparent way
correlates the size of the field gradient with chemical properties of the
system.Comment: 10 page
Methods and prospects for gravitational wave searches targeting ultralight vector boson clouds around known black holes
Ultralight bosons are predicted in many extensions to the Standard Model and
are popular dark matter candidates. The black hole superradiance mechanism
allows for these particles to be probed using only their gravitational
interaction. In this scenario, an ultralight boson cloud may form spontaneously
around a spinning black hole and extract a non-negligible fraction of the black
hole's mass. These oscillating clouds produce quasi-monochromatic,
long-duration gravitational waves that may be detectable by ground-based or
space-based gravitational wave detectors. We discuss the capability of a new
long-duration signal tracking method, based on a hidden Markov model, to detect
gravitational wave signals generated by ultralight vector boson clouds,
including cases where the signal frequency evolution timescale is much shorter
than that of a typical continuous wave signal. We quantify the detection
horizon distances for vector boson clouds with current- and next-generation
ground-based detectors. We demonstrate that vector clouds hosted by black holes
with mass and spin are within the reach of
current-generation detectors up to a luminosity distance of Gpc. This
search method enables one to target vector boson clouds around remnant black
holes from compact binary mergers detected by gravitational-wave detectors. We
discuss the impact of the sky localization of the merger events and demonstrate
that a typical remnant black hole reasonably well-localized by the current
generation detector network is accessible in a follow-up search.Comment: 21 pages, 12 figure
The very faint X-ray binary IGR J17062-6143: a truncated disc, no pulsations, and a possible outflow
We present a comprehensive X-ray study of the neutron star low-mass X-ray binary IGR J17062-6143, which has been accreting at low luminosities since its discovery in 2006. Analysing NuSTAR, XMM–Newton, and Swift observations, we investigate the very faint nature of this source through three approaches: modelling the relativistic reflection spectrum to constrain the accretion geometry, performing high-resolution X-ray spectroscopy to search for an outflow, and searching for the recently reported millisecond X-ray pulsations. We find a strongly truncated accretion disc at
77+22−18
gravitational radii (∼164 km) assuming a high inclination, although a low inclination and a disc extending to the neutron star cannot be excluded. The high-resolution spectroscopy reveals evidence for oxygen-rich circumbinary material, possibly resulting from a blueshifted, collisionally ionized outflow. Finally, we do not detect any pulsations. We discuss these results in the broader context of possible explanations for the persistent faint nature of weakly accreting neutron stars. The results are consistent with both an ultra-compact binary orbit and a magnetically truncated accretion flow, although both cannot be unambiguously inferred. We also discuss the nature of the donor star and conclude that it is likely a CO or O–Ne–Mg white dwarf, consistent with recent multiwavelength modelling
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