10,453 research outputs found
Stochastic backgrounds of gravitational waves and spherical detectors
The analysis of how a stochastic background of gravitational radiation
interacts with a spherical detector is given in detail, which leads to explicit
expressions for the system response functions, as well as for the
cross-correlation matrix of different readout channels. It is shown that
distinctive features of GW induced random detector excitations, relative to
locally generated noise, are in practice insufficient to separate the signal
from the noise by means of a single sphere, if prior knowledge on the GW
spectral density is nil. The situation significantly improves when such
previous knowledge is available, due to the omnidirectionality and multimode
capacities of a spherical GW antenna.Comment: 19 page
All-sky search algorithms for monochromatic signals in resonant bar GW detector data
In this paper we design and develop several filtering strategies for the
analysis of data generated by a resonant bar Gravitational Wave (GW) antenna,
with the goal to assess the presence (or absence) in them of long duration
monochromatic GW signals, as well as their eventual amplitude and frequency,
within the sensitivity band of the detector. Such signals are most likely
generated in the fast rotation of slightly asymmetric spinning stars. We shall
develop the practical procedures, together with the study of their statistical
properties, which will provide us with useful information on each technique's
performance. The selection of candidate events will then be established
according to threshold-crossing probabilities, based on the Neyman-Pearson
criterion. In particular, it will be shown that our approach, based on phase
estimation, presents better signal-to-noise ratio than the most common one of
pure spectral analysis.Comment: 17 pages, 10 PS figures, psbox, MNRAS TeX, submitted to MNRAS,
revised 22-june-1998, full quality figures available compressed at
ftp://fismat.ffn.ub.es/pub/papers/gr-qc/fig_9804026.zi
Scalar QNMs for higher dimensional black holes surrounded by quintessence in Rastall gravity
The spacetime solution for a black hole, surrounded by an exotic matter
field, in Rastall gravity, is calculated in an arbitrary d-dimensional
spacetime. After this, we calculate the scalar quasinormal modes of such
solution, and study the shift on the modes caused by the modification of the
theory of gravity, i.e., by the introduction of a new term due to Rastall. We
conclude that the shift strongly depends on the kind of exotic field one is
studying, but for a low density matter that supposedly pervades the universe,
it is unlikely that Rastall gravity will cause any instability on the probe
field.Comment: 6 figures, 11 page
Evidence for Antipodal Hot Spots During X-ray Bursts From 4U 1636-536
The discovery of high-frequency brightness oscillations in thermonuclear
X-ray bursts from several neutron-star low-mass X-ray binaries has important
implications for the beat frequency model of kilohertz quasi-periodic
brightness oscillations, the propagation of nuclear burning, the structure of
the subsurface magnetic fields in neutron stars, and the equation of state of
high-density matter. These implications depend crucially on whether the
observed frequency is the stellar spin frequency or its first overtone. Here we
report an analysis of five bursts from 4U 1636-536 which exhibit strong
oscillations at approximately 580 Hz. We show that combining the data from the
first 0.75 seconds of each of the five bursts yields a signal at 290 Hz that is
significant at the level when the number of trials is taken
into account. This strongly indicates that 290 Hz is the spin frequency of this
neutron star and that 580 Hz is its first overtone, in agreement with other
arguments about this source but in contrast to suggestions in the literature
that 580 Hz is the true spin frequency. The method used here, which is an
algorithm for combining time series data from the five bursts so that the
phases of the 580 Hz oscillations are aligned, may be used in any source to
search for weak oscillations that have frequencies related in a definite way to
the frequency of a strong oscillation.Comment: 9 pages including one figure, uses aaspp4.sty, submitted to The
Astrophysical Journal Letters on September 1
Errors on the inverse problem solution for a noisy spherical gravitational wave antenna
A single spherical antenna is capable of measuring the direction and
polarization of a gravitational wave. It is possible to solve the inverse
problem using only linear algebra even in the presence of noise. The simplicity
of this solution enables one to explore the error on the solution using
standard techniques. In this paper we derive the error on the direction and
polarization measurements of a gravitational wave. We show that the solid angle
error and the uncertainty on the wave amplitude are direction independent. We
also discuss the possibility of determining the polarization amplitudes with
isotropic sensitivity for any given gravitational wave source.Comment: 13 pages, 4 figures, LaTeX2e, IOP style, submitted to CQ
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