38 research outputs found
Optimizing Advanced Ligo\u27s Scientific Output with Fast, Accurate, Clean Calibration
Since 2015, the direct observation of gravitational waves has opened a new window to observe the universe and made strong-field tests of Einstein\u27s general theory of relativity possible for the first time. During the first two observing runs of the Advanced gravitational-wave detector network, the Laser Interferometer Gravitational-wave Observatory (LIGO) and the Virgo detector have made 10 detections of binary black hole mergers and one detection of a binary neutron star merger with a coincident gamma-ray burst. This dissertation discusses methods used in low and high latency to produce Advanced LIGO\u27s calibrated strain data, highlighting improvements to accuracy, latency, and noise reduction that have been made since the beginning of the second observing run (O2).
Systematic errors in the calibration during O2 varied by frequency, but were generally no greater that 5% in amplitude and 3 deg in phase from 20 Hz to 1 kHz. Due in part to this work, it is now possible to achieve calibration accuracy at the level of ~1% in amplitude and ~1 deg in phase, offering improvements to downstream astrophysical analyses. Since the beginning of O2, latency intrinsic to the calibration procedure has decreased from ~12 s to ~3 s. As latency in data distribution and the sending of automated alerts to astronomers is minimized, reduction in calibration latency will become important for follow-up of events like the binary neutron star merger GW170817. A method of removing spectral lines and broadband noise in the calibration procedure has been developed since O2, offering increases in total detectable volume during future observing runs. High-latency subtraction of lines and broadband noise had a large impact on astrophysical analyses during O2. A similar data product can now be made available in low latency for the first time
Calibration Uncertainty for Advanced LIGO's First and Second Observing Runs
Calibration of the Advanced LIGO detectors is the quantification of the
detectors' response to gravitational waves. Gravitational waves incident on the
detectors cause phase shifts in the interferometer laser light which are read
out as intensity fluctuations at the detector output. Understanding this
detector response to gravitational waves is crucial to producing accurate and
precise gravitational wave strain data. Estimates of binary black hole and
neutron star parameters and tests of general relativity require well-calibrated
data, as miscalibrations will lead to biased results. We describe the method of
producing calibration uncertainty estimates for both LIGO detectors in the
first and second observing runs.Comment: 15 pages, 21 figures, LIGO DCC P160013
Characterization of systematic error in Advanced LIGO calibration
The raw outputs of the detectors within the Advanced Laser Interferometer
Gravitational-Wave Observatory need to be calibrated in order to produce the
estimate of the dimensionless strain used for astrophysical analyses. The two
detectors have been upgraded since the second observing run and finished the
year-long third observing run. Understanding, accounting, and/or compensating
for the complex-valued response of each part of the upgraded detectors improves
the overall accuracy of the estimated detector response to gravitational waves.
We describe improved understanding and methods used to quantify the response of
each detector, with a dedicated effort to define all places where systematic
error plays a role. We use the detectors as they stand in the first half (six
months) of the third observing run to demonstrate how each identified
systematic error impacts the estimated strain and constrain the statistical
uncertainty therein. For this time period, we estimate the upper limit on
systematic error and associated uncertainty to be in magnitude and deg in phase ( confidence interval) in the most sensitive frequency
band 20-2000 Hz. The systematic error alone is estimated at levels of
in magnitude and deg in phase
Characterization of systematic error in Advanced LIGO calibration
The raw outputs of the detectors within the Advanced Laser Interferometer Gravitational-Wave Observatory need to be calibrated in order to produce the estimate of the dimensionless strain used for astrophysical analyses. The two detectors have been upgraded since the second observing run and finished the year-long third observing run. Understanding, accounting, and/or compensating for the complex-valued response of each part of the upgraded detectors improves the overall accuracy of the estimated detector response to gravitational waves. We describe improved understanding and methods used to quantify the response of each detector, with a dedicated effort to define all places where systematic error plays a role. We use the detectors as they stand in the first half (six months) of the third observing run to demonstrate how each identified systematic error impacts the estimated strain and constrain the statistical uncertainty therein. For this time period, we estimate the upper limit on systematic error and associated uncertainty to be <7% in magnitude and <4 deg in phase (68% confidence interval) in the most sensitive frequency band 20-2000 Hz. The systematic error alone is estimated at levels of <2% in magnitude and <2 deg in phase.VB and EP acknowledge
the support of the ARC Center of Excellence for Gravitational Wave Discovery (OzGrav),
Grant Number CE170100004. PBC acknowledges the support of the Spanish Agencia Estatal
de Investigaci´on and Ministerio de Ciencia, Innovaci´on y Universidades grants FPA2016-
76821-P the Vicepresidencia i Conselleria d’Innovaci´o, Recerca i Turisme del Govern de
les Illes Balears (Grant FPI-CAIB FPI/2134/2018), the Fons Social Europeu 2014–2020 de
les Illes Balears, the European Union FEDER funds, and the EU COST actions CA16104,
CA16214, CA17137 and CA18108. The authors would like to thank all of the essential
workers who put their health at risk during the COVID-19 pandemic, without whom we
would not have been able to complete this work. This paper carries LIGO Document Number
LIGO–P1900245
A binary tree approach to template placement for searches for gravitational waves from compact binary mergers
We demonstrate a new geometric method for fast template placement for
searches for gravitational waves from the inspiral, merger and ringdown of
compact binaries. The method is based on a binary tree decomposition of the
template bank parameter space into non-overlapping hypercubes. We use a
numerical approximation of the signal overlap metric at the center of each
hypercube to estimate the number of templates required to cover the hypercube
and determine whether to further split the hypercube. As long as the expected
number of templates in a given cube is greater than a given threshold, we split
the cube along its longest edge according to the metric. When the expected
number of templates in a given hypercube drops below this threshold, the
splitting stops and a template is placed at the center of the hypercube. Using
this method, we generate aligned-spin template banks covering the mass range
suitable for a search of Advanced LIGO data. The aligned-spin bank required ~24
CPU-hours and produced 2 million templates. In general, we find that other
methods, namely stochastic placement, produces a more strictly bounded loss in
match between waveforms, with the same minimal match between waveforms
requiring about twice as many templates with our proposed algorithm. Though we
note that the average match is higher, which would lead to a higher detection
efficiency. Our primary motivation is not to strictly minimize the number of
templates with this algorithm, but rather to produce a bank with useful
geometric properties in the physical parameter space coordinates. Such
properties are useful for population modeling and parameter estimation
Template bank for compact binary mergers in the fourth observing run of Advanced LIGO, Advanced Virgo, and KAGRA
Template banks containing gravitational wave (GW) waveforms are essential for
matched-filtering GW search pipelines. We describe the generation method, the
design, and validation of the template bank used by the GstLAL-based inspiral
pipeline to analyze data from the fourth observing run of LIGO scientific,
Virgo, and KAGRA collaboration. This paper presents a template bank containing
templates that include merging neutron star - neutron star,
neutron star - black hole, and black hole - black hole systems up to a total
mass of . Motivated by observations, component masses below
have dimensionless spins ranging between , while component
masses between to have dimensionless spins ranging between
, where we assume spin-aligned systems. The low-frequency cutoff is
Hz. The templates are placed in the parameter space according to the
metric via a binary tree approach which took
minutes when jobs were parallelized. The template bank generated with this
method has a match or higher for of the injections, thus being as
effective as the template placement method used for the previous observation
runs. The volumes of the templates are computed prior to template placement and
the nearby templates have similar volumes in the coordinate space, henceforth,
enabling a more efficient and less biased implementation of population models.
SVD sorting of the O4 template bank has been renewed to use post-Newtonian
phase terms, which improved the computational efficiency of SVD by nearly times as compared to conventional SVD sorting schemes. Template banks
and searches focusing on the sub-solar mass parameter space and
intermediate-mass black hole parameter space are conducted separately
When to Point Your Telescopes: Gravitational Wave Trigger Classification for Real-Time Multi-Messenger Followup Observations
We develop a robust and self-consistent framework to extract and classify
gravitational wave candidates from noisy data, for the purpose of assisting in
real-time multi-messenger follow-ups during LIGO-Virgo-KAGRA's fourth observing
run~(O4). Our formalism implements several improvements to the low latency
calculation of the probability of astrophysical origin~(\PASTRO{}), so as to
correctly account for various factors such as the sensitivity change between
observing runs, and the deviation of the recovered template waveform from the
true gravitational wave signal that can strongly bias said calculation. We
demonstrate the high accuracy with which our new formalism recovers and
classifies gravitational wave triggers, by analyzing replay data from previous
observing runs injected with simulated sources of different categories. We show
that these improvements enable the correct identification of the majority of
simulated sources, many of which would have otherwise been misclassified. We
carry out the aforementioned analysis by implementing our formalism through the
\GSTLAL{} search pipeline even though it can be used in conjunction with
potentially any matched filtering pipeline. Armed with robust and
self-consistent \PASTRO{} values, the \GSTLAL{} pipeline can be expected to
provide accurate source classification information for assisting in
multi-messenger follow-up observations to gravitational wave alerts sent out
during O4.Comment: v2 upload was accidental. revert back to v