331 research outputs found
Reconstruction of source location in a network of gravitational wave interferometric detectors
This paper deals with the reconstruction of the direction of a gravitational
wave source using the detection made by a network of interferometric detectors,
mainly the LIGO and Virgo detectors. We suppose that an event has been seen in
coincidence using a filter applied on the three detector data streams. Using
the arrival time (and its associated error) of the gravitational signal in each
detector, the direction of the source in the sky is computed using a chi^2
minimization technique. For reasonably large signals (SNR>4.5 in all
detectors), the mean angular error between the real location and the
reconstructed one is about 1 degree. We also investigate the effect of the
network geometry assuming the same angular response for all interferometric
detectors. It appears that the reconstruction quality is not uniform over the
sky and is degraded when the source approaches the plane defined by the three
detectors. Adding at least one other detector to the LIGO-Virgo network reduces
the blind regions and in the case of 6 detectors, a precision less than 1
degree on the source direction can be reached for 99% of the sky.Comment: Accepted in Phys. Rev.
A comparison of methods for gravitational wave burst searches from LIGO and Virgo
The search procedure for burst gravitational waves has been studied using 24
hours of simulated data in a network of three interferometers (Hanford 4-km,
Livingston 4-km and Virgo 3-km are the example interferometers). Several
methods to detect burst events developed in the LIGO Scientific Collaboration
(LSC) and Virgo collaboration have been studied and compared. We have performed
coincidence analysis of the triggers obtained in the different interferometers
with and without simulated signals added to the data. The benefits of having
multiple interferometers of similar sensitivity are demonstrated by comparing
the detection performance of the joint coincidence analysis with LSC and Virgo
only burst searches. Adding Virgo to the LIGO detector network can increase by
50% the detection efficiency for this search. Another advantage of a joint
LIGO-Virgo network is the ability to reconstruct the source sky position. The
reconstruction accuracy depends on the timing measurement accuracy of the
events in each interferometer, and is displayed in this paper with a fixed
source position example.Comment: LIGO-Virgo working group submitted to PR
A First Comparison Between LIGO and Virgo Inspiral Search Pipelines
This article reports on a project that is the first step the LIGO Scientific
Collaboration and the Virgo Collaboration have taken to prepare for the mutual
search for inspiral signals. The project involved comparing the analysis
pipelines of the two collaborations on data sets prepared by both sides,
containing simulated noise and injected events. The ability of the pipelines to
detect the injected events was checked, and a first comparison of how the
parameters of the events were recovered has been completed.Comment: GWDAW-9 proceeding
A first comparison of search methods for gravitational wave bursts using LIGO and Virgo simulated data
We present a comparative study of 6 search methods for gravitational wave
bursts using simulated LIGO and Virgo noise data. The data's spectra were
chosen to follow the design sensitivity of the two 4km LIGO interferometers and
the 3km Virgo interferometer. The searches were applied on replicas of the data
sets to which 8 different signals were injected. Three figures of merit were
employed in this analysis: (a) Receiver Operator Characteristic curves, (b)
necessary signal to noise ratios for the searches to achieve 50 percent and 90
percent efficiencies, and (c) variance and bias for the estimation of the
arrival time of a gravitational wave burst.Comment: GWDAW9 proceeding
Benefits of joint LIGO -- Virgo coincidence searches for burst and inspiral signals
We examine the benefits of performing a joint LIGO--Virgo search for
transient signals. We do this by adding burst and inspiral signals to 24 hours
of simulated detector data. We find significant advantages to performing a
joint coincidence analysis, above either a LIGO only or Virgo only search.
These include an increased detection efficiency, at a fixed false alarm rate,
to both burst and inspiral events and an ability to reconstruct the sky
location of a signal.Comment: 11 pages 8 figures, Amaldi 6 proceeding
Data Analysis Challenges for the Einstein Telescope
The Einstein Telescope is a proposed third generation gravitational wave
detector that will operate in the region of 1 Hz to a few kHz. As well as the
inspiral of compact binaries composed of neutron stars or black holes, the
lower frequency cut-off of the detector will open the window to a number of new
sources. These will include the end stage of inspirals, plus merger and
ringdown of intermediate mass black holes, where the masses of the component
bodies are on the order of a few hundred solar masses. There is also the
possibility of observing intermediate mass ratio inspirals, where a stellar
mass compact object inspirals into a black hole which is a few hundred to a few
thousand times more massive. In this article, we investigate some of the data
analysis challenges for the Einstein Telescope such as the effects of increased
source number, the need for more accurate waveform models and the some of the
computational issues that a data analysis strategy might face.Comment: 18 pages, Invited review for Einstein Telescope special edition of
GR
H.E.S.S. observations of gamma-ray bursts in 2003-2007
Very-high-energy (VHE; >~100 GeV) gamma-rays are expected from gamma-ray
bursts (GRBs) in some scenarios. Exploring this photon energy regime is
necessary for understanding the energetics and properties of GRBs. GRBs have
been one of the prime targets for the H.E.S.S. experiment, which makes use of
four Imaging Atmospheric Cherenkov Telescopes (IACTs) to detect VHE gamma-rays.
Dedicated observations of 32 GRB positions were made in the years 2003-2007 and
a search for VHE gamma-ray counterparts of these GRBs was made. Depending on
the visibility and observing conditions, the observations mostly start minutes
to hours after the burst and typically last two hours. Results from
observations of 22 GRB positions are presented and evidence of a VHE signal was
found neither in observations of any individual GRBs, nor from stacking data
from subsets of GRBs with higher expected VHE flux according to a
model-independent ranking scheme. Upper limits for the VHE gamma-ray flux from
the GRB positions were derived. For those GRBs with measured redshifts,
differential upper limits at the energy threshold after correcting for
absorption due to extra-galactic background light are also presented.Comment: 9 pages, 4 tables, 3 figure
Explaining the social gradient in smoking and cessation: the peril and promise of social mobility
Smoking in high-income countries is now concentrated in poor communities whose relatively high smoking prevalence is explained by greater uptake but above all by lower quit rates. Whilst a number of barriers to smoking cessation have been identified, this is the first paper to situate cessation itself as a classed and cultural practice. Drawing on ethnographic research carried out in a working class community in the North of England between 2012 and 2015, I theorise smoking cessation as a symbolic practice in relation to the affective experience of class and social mobility. I show that ambivalence about upward mobility as separation and loss translated into ambivalence about smoking cessation. The reason for this was that the social gradient in smoking operated dynamically at the level of the individual life course i.e. smoking cessation followed upward mobility. A serious health problem was an appropriate reason to quit but older women continued to smoke despite serious health problems. This was linked to historical gender roles leading to women placing a low priority on their own health as well as the intergenerational reproduction of smoking through close affective links with smoking parents
Discovery of VHE gamma-rays from the high-frequency-peaked BL Lac object RGB J0152+017
Aims: The BL Lac object RGB J0152+017 (z=0.080) was predicted to be a very
high-energy (VHE; > 100 GeV) gamma-ray source, due to its high X-ray and radio
fluxes. Our aim is to understand the radiative processes by investigating the
observed emission and its production mechanism using the High Energy
Stereoscopic System (H.E.S.S.) experiment. Methods: We report recent
observations of the BL Lac source RGB J0152+017 made in late October and
November 2007 with the H.E.S.S. array consisting of four imaging atmospheric
Cherenkov telescopes. Contemporaneous observations were made in X-rays by the
Swift and RXTE satellites, in the optical band with the ATOM telescope, and in
the radio band with the Nancay Radio Telescope. Results: A signal of 173
gamma-ray photons corresponding to a statistical significance of 6.6 sigma was
found in the data. The energy spectrum of the source can be described by a
powerlaw with a spectral index of 2.95+/-0.36stat+/-0.20syst. The integral flux
above 300 GeV corresponds to ~2% of the flux of the Crab nebula. The source
spectral energy distribution (SED) can be described using a two-component
non-thermal synchrotron self-Compton (SSC) leptonic model, except in the
optical band, which is dominated by a thermal host galaxy component. The
parameters that are found are very close to those found in similar SSC studies
in TeV blazars. Conclusions: RGB J0152+017 is discovered as a source of VHE
gamma-rays by H.E.S.S. The location of its synchrotron peak, as derived from
the SED in Swift data, allows clearly classification it as a
high-frequency-peaked BL Lac (HBL).Comment: Accepted for publication in A&A Letters (5 pages, 4 figures
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