978 research outputs found
A new code for parameter estimation in searches for gravitational waves from known pulsars
We describe the consistency testing of a new code for gravitational wave
signal parameter estimation in known pulsar searches. The code uses an
implementation of nested sampling to explore the likelihood volume. Using fake
signals and simulated noise we compare this to a previous code that calculated
the signal parameter posterior distributions on both a grid and using a crude
Markov chain Monte Carlo (MCMC) method. We define a new parameterisation of two
orientation angles of neutron stars used in the signal model (the initial phase
and polarisation angle), which breaks a degeneracy between them and allows more
efficient exploration of those parameters. Finally, we briefly describe
potential areas for further study and the uses of this code in the future.Comment: Accepted for proceedings of Amaldi 9 meetin
An Evidence Based Time-Frequency Search Method for Gravitational Waves from Pulsar Glitches
We review and expand on a Bayesian model selection technique for the
detection of gravitational waves from neutron star ring-downs associated with
pulsar glitches. The algorithm works with power spectral densities constructed
from overlapping time segments of gravitational wave data. Consequently, the
original approach was at risk of falsely identifying multiple signals where
only one signal was present in the data. We introduce an extension to the
algorithm which uses posterior information on the frequency content of detected
signals to cluster events together. The requirement that we have just one
detection per signal is now met with the additional bonus that the belief in
the presence of a signal is boosted by incorporating information from adjacent
time segments.Comment: 6 pages, 4 figures, submitted to AMALDI 7 proceeding
Comparative in vitro studies on the immunosuppressive activities of mycophenolic acid, bredinin, FK 506, cyclosporine, and rapamycin
Robust Bayesian detection of unmodelled bursts
A Bayesian treatment of the problem of detecting an unmodelled gravitational
wave burst with a global network of gravitational wave observatories reveals
that several previously proposed statistics have implicit biases that render
them sub-optimal for realistic signal populations.Comment: 9 pages, 1 figure, submitted to CQG Amaldi proceedings special issu
Optimal time-domain combination of the two calibrated output quadratures of GEO 600
GEO 600 is an interferometric gravitational wave detector with a 600 m arm-length and which uses a dual-recycled optical configuration to give enhanced sensitivity over certain frequencies in the detection band. Due to the dual-recycling, GEO 600 has two main output signals, both of which potentially contain gravitational wave signals. These two outputs are calibrated to strain using a time-domain method. In order to simplify the analysis of the GEO 600 data set, it is desirable to combine these two calibrated outputs to form a single strain signal that has optimal signal-to-noise ratio across the detection band. This paper describes a time-domain method for doing this combination. The method presented is similar to one developed for optimally combining the outputs of two colocated gravitational wave detectors. In the scheme presented in this paper, some simplifications are made to allow its implementation using time-domain methods
The liver allograft, chronic (ductopenic) rejection, and microchimerism: What can they teach us?
Current status of gravitational-wave observations
The first generation of gravitational wave interferometric detectors has
taken data at, or close to, their design sensitivity. This data has been
searched for a broad range of gravitational wave signatures. An overview of
gravitational wave search methods and results are presented. Searches for
gravitational waves from unmodelled burst sources, compact binary coalescences,
continuous wave sources and stochastic backgrounds are discussed.Comment: 21 pages, LaTeX, uses svjour3.cls, 1 figure, for GRG special issue on
Einstein Telescop
Upper Limits On Periodic, Pulsed Radio Emission from the X-Ray Point Source in Cassiopeia A
The Chandra X-ray Observatory recently discovered an X-ray point source near
the center of Cassiopeia A, the youngest known Galactic supernova remnant. We
have conducted a sensitive search for radio pulsations from this source with
the Very Large Array, taking advantage of the high angular resolution of the
array to resolve out the emission from the remnant itself. No convincing
signatures of a dispersed, periodic source or of isolated dispersed pulses were
found, whether for an isolated or a binary source. We derive upper limits of 30
and 1.3 mJy at 327 and 1435 MHz for the phase-averaged pulsed flux density from
this source. The corresponding luminosity limits are lower than those for any
pulsar with age less than 10^4 years. The sensitivities of our search to single
pulses were 25 and 1.0 Jy at 327 and 1435 MHz. For comparison, the Crab pulsar
emits roughly 80 pulses per minute with flux densities greater than 100 Jy at
327 MHz and 8 pulses per minute with flux densities greater than 50 Jy at 1435
MHz. These limits are consistent with the suggestion that the X-ray point
source in Cas A adds to the growing number of neutron stars which are not radio
pulsars.Comment: accepted by ApJ Letter
- …