2,269 research outputs found
Identifying the Host Galaxy of Gravitational Wave Signals
One of the goals of the current LIGO-GEO-Virgo science run is to identify
transient gravitational wave (GW) signals in near real time to allow follow-up
electromagnetic (EM) observations. An EM counterpart could increase the
confidence of the GW detection and provide insight into the nature of the
source. Current GW-EM campaigns target potential host galaxies based on overlap
with the GW sky error box. We propose a new statistic to identify the most
likely host galaxy, ranking galaxies based on their position, distance, and
luminosity. We test our statistic with Monte Carlo simulations of GWs produced
by coalescing binaries of neutron stars (NS) and black holes (BH), one of the
most promising sources for ground-based GW detectors. Considering signals
accessible to current detectors, we find that when imaging a single galaxy, our
statistic correctly identifies the true host ~20% to ~50% of the time,
depending on the masses of the binary components. With five narrow-field images
the probability of imaging the true host increases to ~50% to ~80%. When
collectively imaging groups of galaxies using large field-of-view telescopes,
the probability improves to ~30% to ~60% for a single image and to ~70% to ~90%
for five images. For the advanced generation of detectors (c. 2015+), and
considering binaries within 100 Mpc (the reach of the galaxy catalogue used),
the probability is ~40% for one narrow-field image, ~75% for five narrow-field
images, ~65% for one wide-field image, and ~95% for five wide-field images,
irrespective of binary type.Comment: 5 pages, 2 figure
Improving the Sensitivity of Advanced LIGO Using Noise Subtraction
This paper presents an adaptable, parallelizable method for subtracting
linearly coupled noise from Advanced LIGO data. We explain the features
developed to ensure that the process is robust enough to handle the variability
present in Advanced LIGO data. In this work, we target subtraction of noise due
to beam jitter, detector calibration lines, and mains power lines. We
demonstrate noise subtraction over the entirety of the second observing run,
resulting in increases in sensitivity comparable to those reported in previous
targeted efforts. Over the course of the second observing run, we see a 30%
increase in Advanced LIGO sensitivity to gravitational waves from a broad range
of compact binary systems. We expect the use of this method to result in a
higher rate of detected gravitational-wave signals in Advanced LIGO data.Comment: 15 pages, 6 figure
The Issues of Mismodelling Gravitational-Wave Data for Parameter Estimation
Bayesian inference is used to extract unknown parameters from gravitational
wave signals. Detector noise is typically modelled as stationary, although data
from the LIGO and Virgo detectors is not stationary. We demonstrate that the
posterior of estimated waveform parameters is no longer valid under the
assumption of stationarity. We show that while the posterior is unbiased, the
errors will be under- or overestimated compared to the true posterior. A
formalism was developed to measure the effect of the mismodelling, and found
the effect of any form of non-stationarity has an effect on the results, but
are not significant in certain circumstances. We demonstrate the effect of
short-duration Gaussian noise bursts and persistent oscillatory modulation of
the noise on binary-black-hole-like signals. In the case of short signals,
non-stationarity in the data does not have a large effect on the parameter
estimation, but the errors from non-stationary data containing signals lasting
tens of seconds or longer will be several times worse than if the noise was
stationary. Accounting for this limiting factor in parameter sensitivity could
be very important for achieving accurate astronomical results, including an
estimation of the Hubble parameter. This methodology for handling the
non-stationarity will also be invaluable for analysis of waveforms that last
minutes or longer, such as those we expect to see with the Einstein Telescope.Comment: 15 pages, 5 figures. Comments welcom
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The c-terminal extension of a hybrid immunoglobulin A/G heavy chain is responsible for its Golgi-mediated sorting to the vacuole
We have assessed the ability of the plant secretory pathway to handle the expression of complex heterologous proteins by investigating the fate of a hybrid immunoglobulin A/G in tobacco cells. Although plant cells can express large amounts of the antibody, a relevant proportion is normally lost to vacuolar sorting and degradation. Here we show that the synthesis of high amounts of IgA/G does not impose stress on the plant secretory pathway. Plant cells can assemble antibody chains with high efficiency and vacuolar transport occurs only after the assembled immunoglobulins have traveled through the Golgi complex. We prove that vacuolar delivery of IgA/G depends on the presence of a cryptic sorting signal in the tailpiece of the IgA/G heavy chain. We also show that unassembled light chains are efficiently secreted as monomers by the plant secretory pathway
Large-Scale Image Processing with the ROTSE Pipeline for Follow-Up of Gravitational Wave Events
Electromagnetic (EM) observations of gravitational-wave (GW) sources would
bring unique insights into a source which are not available from either channel
alone. However EM follow-up of GW events presents new challenges. GW events
will have large sky error regions, on the order of 10-100 square degrees, which
can be made up of many disjoint patches. When searching such large areas there
is potential contamination by EM transients unrelated to the GW event.
Furthermore, the characteristics of possible EM counterparts to GW events are
also uncertain. It is therefore desirable to be able to assess the statistical
significance of a candidate EM counterpart, which can only be done by
performing background studies of large data sets. Current image processing
pipelines such as that used by ROTSE are not usually optimised for large-scale
processing. We have automated the ROTSE image analysis, and supplemented it
with a post-processing unit for candidate validation and classification. We
also propose a simple ad hoc statistic for ranking candidates as more likely to
be associated with the GW trigger. We demonstrate the performance of the
automated pipeline and ranking statistic using archival ROTSE data. EM
candidates from a randomly selected set of images are compared to a background
estimated from the analysis of 102 additional sets of archival images. The
pipeline's detection efficiency is computed empirically by re-analysis of the
images after adding simulated optical transients that follow typical light
curves for gamma-ray burst afterglows and kilonovae. We show that the automated
pipeline rejects most background events and is sensitive to simulated
transients to limiting magnitudes consistent with the limiting magnitude of the
images
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