60 research outputs found
Implementation and testing of the first prompt search for gravitational wave transients with electromagnetic counterparts
Aims. A transient astrophysical event observed in both gravitational wave
(GW) and electromagnetic (EM) channels would yield rich scientific rewards. A
first program initiating EM follow-ups to possible transient GW events has been
developed and exercised by the LIGO and Virgo community in association with
several partners. In this paper, we describe and evaluate the methods used to
promptly identify and localize GW event candidates and to request images of
targeted sky locations.
Methods. During two observing periods (Dec 17 2009 to Jan 8 2010 and Sep 2 to
Oct 20 2010), a low-latency analysis pipeline was used to identify GW event
candidates and to reconstruct maps of possible sky locations. A catalog of
nearby galaxies and Milky Way globular clusters was used to select the most
promising sky positions to be imaged, and this directional information was
delivered to EM observatories with time lags of about thirty minutes. A Monte
Carlo simulation has been used to evaluate the low-latency GW pipeline's
ability to reconstruct source positions correctly.
Results. For signals near the detection threshold, our low-latency algorithms
often localized simulated GW burst signals to tens of square degrees, while
neutron star/neutron star inspirals and neutron star/black hole inspirals were
localized to a few hundred square degrees. Localization precision improves for
moderately stronger signals. The correct sky location of signals well above
threshold and originating from nearby galaxies may be observed with ~50% or
better probability with a few pointings of wide-field telescopes.Comment: 17 pages. This version (v2) includes two tables and 1 section not
included in v1. Accepted for publication in Astronomy & Astrophysic
Search for Gravitational Waves from Low Mass Compact Binary Coalescence in LIGO's Sixth Science Run and Virgo's Science Runs 2 and 3
We report on a search for gravitational waves from coalescing compact
binaries using LIGO and Virgo observations between July 7, 2009 and October 20,
2010. We searched for signals from binaries with total mass between 2 and 25
solar masses; this includes binary neutron stars, binary black holes, and
binaries consisting of a black hole and neutron star. The detectors were
sensitive to systems up to 40 Mpc distant for binary neutron stars, and further
for higher mass systems. No gravitational-wave signals were detected. We report
upper limits on the rate of compact binary coalescence as a function of total
mass, including the results from previous LIGO and Virgo observations. The
cumulative 90%-confidence rate upper limits of the binary coalescence of binary
neutron star, neutron star- black hole and binary black hole systems are 1.3 x
10^{-4}, 3.1 x 10^{-5} and 6.4 x 10^{-6} Mpc^{-3}yr^{-1}, respectively. These
upper limits are up to a factor 1.4 lower than previously derived limits. We
also report on results from a blind injection challenge.Comment: 11 pages, 5 figures. For a repository of data used in the
publication, go to:
. Also see the
announcement for this paper on ligo.org at:
<http://www.ligo.org/science/Publication-S6CBCLowMass/index.php
Search for gravitational waves associated with the InterPlanetary Network short gamma ray bursts
We outline the scientific motivation behind a search for gravitational waves
associated with short gamma ray bursts detected by the InterPlanetary Network
(IPN) during LIGO's fifth science run and Virgo's first science run. The IPN
localisation of short gamma ray bursts is limited to extended error boxes of
different shapes and sizes and a search on these error boxes poses a series of
challenges for data analysis. We will discuss these challenges and outline the
methods to optimise the search over these error boxes.Comment: Methods paper; Proceedings for Eduardo Amaldi 9 Conference on
Gravitational Waves, July 2011, Cardiff, U
Directional limits on persistent gravitational waves using LIGO S5 science data
The gravitational-wave (GW) sky may include nearby pointlike sources as well
as astrophysical and cosmological stochastic backgrounds. Since the relative
strength and angular distribution of the many possible sources of GWs are not
well constrained, searches for GW signals must be performed in a
model-independent way. To that end we perform two directional searches for
persistent GWs using data from the LIGO S5 science run: one optimized for
pointlike sources and one for arbitrary extended sources. The latter result is
the first of its kind. Finding no evidence to support the detection of GWs, we
present 90% confidence level (CL) upper-limit maps of GW strain power with
typical values between 2-20x10^-50 strain^2 Hz^-1 and 5-35x10^-49 strain^2
Hz^-1 sr^-1 for pointlike and extended sources respectively. The limits on
pointlike sources constitute a factor of 30 improvement over the previous best
limits. We also set 90% CL limits on the narrow-band root-mean-square GW strain
from interesting targets including Sco X-1, SN1987A and the Galactic Center as
low as ~7x10^-25 in the most sensitive frequency range near 160 Hz. These
limits are the most constraining to date and constitute a factor of 5
improvement over the previous best limits.Comment: 10 pages, 4 figure
Calibration of the LIGO gravitational wave detectors in the fifth science run
The Laser Interferometer Gravitational Wave Observatory (LIGO) is a network of three detectors built to detect local perturbations in the space–time metric from astrophysical sources. These detectors, two in Hanford, WA and one in Livingston, LA, are power-recycled Fabry-Perot Michelson interferometers. In their fifth science run (S5), between November 2005 and October 2007, these detectors accumulated one year of triple coincident data while operating at their designed sensitivity. In this paper, we describe the calibration of the instruments in the S5 data set, including measurement techniques and uncertainty estimation.United States. National Aeronautics and Space AdministrationCarnegie TrustLeverhulme TrustDavid & Lucile Packard FoundationResearch CorporationAlfred P. Sloan Foundatio
Search for gravitational wave ringdowns from perturbed black holes in LIGO S4 data
According to general relativity a perturbed black hole will settle to a
stationary configuration by the emission of gravitational radiation. Such a
perturbation will occur, for example, in the coalescence of a black hole
binary, following their inspiral and subsequent merger. At late times the
waveform is a superposition of quasi-normal modes, which we refer to as the
ringdown. The dominant mode is expected to be the fundamental mode, l=m=2.
Since this is a well-known waveform, matched filtering can be implemented to
search for this signal using LIGO data. We present a search for gravitational
waves from black hole ringdowns in the fourth LIGO science run S4, during which
LIGO was sensitive to the dominant mode of perturbed black holes with masses in
the range of 10 Msun to 500 Msun, the regime of intermediate-mass black holes,
to distances up to 300 Mpc. We present a search for gravitational waves from
black hole ringdowns using data from S4. No gravitational wave candidates were
found; we place a 90%-confidence upper limit on the rate of ringdowns from
black holes with mass between 85 Msun and 390 Msun in the local universe,
assuming a uniform distribution of sources, of 3.2 x 10^{-5} yr^{-1} Mpc^{-3} =
1.6 x 10^{-3}yr^{-1} L_{10}^{-1}, where L_{10} is 10^{10} times the solar
blue-light luminosity.Comment: 8 pages, 6 figure
The present gravitational wave detection effort
Gravitational radiation offers a new non-electromagnetic window through which to observe the universe. The LIGO and Virgo Collaborations have completed a first joint data run with unprecedented sensitivities to gravitational waves. Results from searches in the data for a variety of astrophysical sources are presented. A second joint data run with improved detector sensitivities is underway, and soon major upgrades will be carried out to build Advanced LIGO and Advanced Virgo with expected improvements in event rates of more than 1000. In parallel there is a vigorous effort in the radio pulsar community to detect nHz gravitational waves via the timing residuals in an array of pulsars at different locations in the sky.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/85430/1/jpconf10_203_012002.pd
Sensitivity Achieved by the LIGO and Virgo Gravitational Wave Detectors during LIGO's Sixth and Virgo's Second and Third Science Runs
We summarize the sensitivity achieved by the LIGO and Virgo gravitational wave detectors for low-mass compact binary coalescence (CBC) searches during LIGO's sixth science run and Virgo's second and third science runs. We present strain noise power spectral densities (PSDs) which are representative of the typical performance achieved by the detectors in these science runs. The data presented here and in the accompanying web-accessible data files are intended to be released to the public as a summary of detector performance for low-mass CBC searches during S6 and VSR2-3
All-sky Search for Periodic Gravitational Waves in the Full S5 LIGO Data
We report on an all-sky search for periodic gravitational waves in the
frequency band 50-800 Hz and with the frequency time derivative in the range of
0 through -6e-9 Hz/s. Such a signal could be produced by a nearby spinning and
slightly non-axisymmetric isolated neutron star in our galaxy. After recent
improvements in the search program that yielded a 10x increase in computational
efficiency, we have searched in two years of data collected during LIGO's fifth
science run and have obtained the most sensitive all-sky upper limits on
gravitational wave strain to date. Near 150 Hz our upper limit on worst-case
linearly polarized strain amplitude is 1e-24, while at the high end of
our frequency range we achieve a worst-case upper limit of 3.8e-24 for all
polarizations and sky locations. These results constitute a factor of two
improvement upon previously published data. A new detection pipeline utilizing
a Loosely Coherent algorithm was able to follow up weaker outliers, increasing
the volume of space where signals can be detected by a factor of 10, but has
not revealed any gravitational wave signals. The pipeline has been tested for
robustness with respect to deviations from the model of an isolated neutron
star, such as caused by a low-mass or long-period binary companion.Comment: 18 page
Guidelines for the use and interpretation of assays for monitoring autophagy (3rd edition)
In 2008 we published the first set of guidelines for standardizing research in autophagy. Since then, research on this topic has continued to accelerate, and many new scientists have entered the field. Our knowledge base and relevant new technologies have also been expanding. Accordingly, it is important to update these guidelines for monitoring autophagy in different organisms. Various reviews have described the range of assays that have been used for this purpose. Nevertheless, there continues to be confusion regarding acceptable methods to measure autophagy, especially in multicellular eukaryotes. For example, a key point that needs to be emphasized is that there is a difference between measurements that monitor the numbers or volume of autophagic elements (e.g., autophagosomes or autolysosomes) at any stage of the autophagic process versus those that measure fl ux through the autophagy pathway (i.e., the complete process including the amount and rate of cargo sequestered and degraded). In particular, a block in macroautophagy that results in autophagosome accumulation must be differentiated from stimuli that increase autophagic activity, defi ned as increased autophagy induction coupled with increased delivery to, and degradation within, lysosomes (inmost higher eukaryotes and some protists such as Dictyostelium ) or the vacuole (in plants and fungi). In other words, it is especially important that investigators new to the fi eld understand that the appearance of more autophagosomes does not necessarily equate with more autophagy. In fact, in many cases, autophagosomes accumulate because of a block in trafficking to lysosomes without a concomitant change in autophagosome biogenesis, whereas an increase in autolysosomes may reflect a reduction in degradative activity. It is worth emphasizing here that lysosomal digestion is a stage of autophagy and evaluating its competence is a crucial part of the evaluation of autophagic flux, or complete autophagy. Here, we present a set of guidelines for the selection and interpretation of methods for use by investigators who aim to examine macroautophagy and related processes, as well as for reviewers who need to provide realistic and reasonable critiques of papers that are focused on these processes. These guidelines are not meant to be a formulaic set of rules, because the appropriate assays depend in part on the question being asked and the system being used. In addition, we emphasize that no individual assay is guaranteed to be the most appropriate one in every situation, and we strongly recommend the use of multiple assays to monitor autophagy. Along these lines, because of the potential for pleiotropic effects due to blocking autophagy through genetic manipulation it is imperative to delete or knock down more than one autophagy-related gene. In addition, some individual Atg proteins, or groups of proteins, are involved in other cellular pathways so not all Atg proteins can be used as a specific marker for an autophagic process. In these guidelines, we consider these various methods of assessing autophagy and what information can, or cannot, be obtained from them. Finally, by discussing the merits and limits of particular autophagy assays, we hope to encourage technical innovation in the field
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