1,700 research outputs found
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posterior of estimated waveform parameters is no longer valid under the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
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
Electromagnetic follow-up of gravitational wave candidates
Observations of astrophysical systems in different wavelengths can reveal insights
in to systems which are not available from a single wavelength. The
same can be expected from multi-channel observations of systems which also
produce gravitational waves (GWs). The most likely source of strong, detectable
GWs, which will also produce an electromagnetic (EM) signature, is
the merger of compact objects containing neutron stars (NS) and black holes
(BH), namely NS-NS and NS-BH systems. The focus of this thesis is to summarise
current and past efforts to detect an EM counterpart of a GW event,
with emphasis on compact merger sources.
To begin, the formulation of GWs in general relativity is brie
y discussed,
as well as the main classes of GW sources. The global networks of GW interferometers
in the recent past and near future are described, together with brief
explanations of operational principles and the main challenges GW detectors
face to make a confident detection.
Current literature is reviewed to give a brief summary of the most promising
sources which produce both GW and EM signals. Emphasis is given to
gamma-ray bursts (GRBs), their afterglows, and kilonovae. In addition a brief
description of GW searches triggered by an external source (such as a GRB) is
given. A new form of search is then discussed in which GW events are used to
point conventional EM telescopes, with emphasis on rapidly slewing, wide field
of view optical telescopes. The main challenge in this form of search is that
timing information from a network of GW interferometers yields large error regions
for the source sky direction making it diffcult to locate an EM transient.
Therefore a new statistic is presented in which galaxies (taken from a galaxy
catalogue) within this search region are ranked. The probability of identifying
the host galaxy of a GW signal from NS-NS and NS-BH systems is investigated
and results presented for past and future GW detector configurations.
The ROTSE-III telescope system took part in this first search for EM counterparts
of GW triggers. With four identical robotic telescopes located across
the world it responded to five GW events. Presented is an automation of the
ROTSE image processing pipeline which allows large-scale processing and automated
validation and classification of candidates. A background study was
conducted to better understand the optical transient background and to determine
the statistical significance of candidates. Pipeline performance is tested
by inserting simulated transients following kilonova and GRB lightcurves in
to images; an efficiency study is described. Finally the results of the images
taken in response to the five GW events are presented and discussed
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
Cost-benefit analysis for commissioning decisions in GEO600
Gravitational wave interferometers are complex instruments, requiring years
of commissioning to achieve the required sensitivities for the detection of
gravitational waves, of order 10^-21 in dimensionless detector strain, in the
tens of Hz to several kHz frequency band. Investigations carried out by the
GEO600 detector characterisation group have shown that detector
characterisation techniques are useful when planning for commissioning work. At
the time of writing, GEO600 is the only large scale laser interferometer
currently in operation running with a high duty factor, 70%, limited chiefly by
the time spent commissioning the detector. The number of observable
gravitational wave sources scales as the product of the volume of space to
which the detector is sensitive and the observation time, so the goal of
commissioning is to improve the detector sensitivity with the least possible
detector down time. We demonstrate a method for increasing the number of
sources observable by such a detector, by assessing the severity of
non-astrophysical noise contaminations to efficiently guide commissioning. This
method will be particularly useful in the early stages and during the initial
science runs of the aLIGO and adVirgo detectors, as they are brought up to
design performance.Comment: 17 pages, 17 figures, 2 table
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