891 research outputs found
Best network chirplet-chain: Near-optimal coherent detection of unmodeled gravitation wave chirps with a network of detectors
The searches of impulsive gravitational waves (GW) in the data of the
ground-based interferometers focus essentially on two types of waveforms: short
unmodeled bursts and chirps from inspiralling compact binaries. There is room
for other types of searches based on different models. Our objective is to fill
this gap. More specifically, we are interested in GW chirps with an arbitrary
phase/frequency vs. time evolution. These unmodeled GW chirps may be considered
as the generic signature of orbiting/spinning sources. We expect quasi-periodic
nature of the waveform to be preserved independent of the physics which governs
the source motion. Several methods have been introduced to address the
detection of unmodeled chirps using the data of a single detector. Those
include the best chirplet chain (BCC) algorithm introduced by the authors. In
the next years, several detectors will be in operation. The joint coherent
analysis of GW by multiple detectors can improve the sight horizon, the
estimation of the source location and the wave polarization angles. Here, we
extend the BCC search to the multiple detector case. The method amounts to
searching for salient paths in the combined time-frequency representation of
two synthetic streams. The latter are time-series which combine the data from
each detector linearly in such a way that all the GW signatures received are
added constructively. We give a proof of principle for the full sky blind
search in a simplified situation which shows that the joint estimation of the
source sky location and chirp frequency is possible.Comment: 22 pages, revtex4, 6 figure
Short GRBs at the dawn of the gravitational wave era
We derive the luminosity function and redshift distribution of short Gamma
Ray Bursts (SGRBs) using (i) all the available observer-frame constraints (i.e.
peak flux, fluence, peak energy and duration distributions) of the large
population of Fermi SGRBs and (ii) the rest-frame properties of a complete
sample of Swift SGRBs. We show that a steep with a>2.0
is excluded if the full set of constraints is considered. We implement a Monte
Carlo Markov Chain method to derive the and functions
assuming intrinsic Ep-Liso and Ep-Eiso correlations or independent
distributions of intrinsic peak energy, luminosity and duration. To make our
results independent from assumptions on the progenitor (NS-NS binary mergers or
other channels) and from uncertainties on the star formation history, we assume
a parametric form for the redshift distribution of SGRBs. We find that a
relatively flat luminosity function with slope ~0.5 below a characteristic
break luminosity ~3 erg/s and a redshift distribution of SGRBs
peaking at z~1.5-2 satisfy all our constraints. These results hold also if no
Ep-Liso and Ep-Eiso correlations are assumed. We estimate that, within ~200 Mpc
(i.e. the design aLIGO range for the detection of GW produced by NS-NS merger
events), 0.007-0.03 SGRBs yr should be detectable as gamma-ray events.
Assuming current estimates of NS-NS merger rates and that all NS-NS mergers
lead to a SGRB event, we derive a conservative estimate of the average opening
angle of SGRBs: ~3-6 deg. Our luminosity function implies an
average luminosity L~1.5 erg/s, nearly two orders of magnitude
higher than previous findings, which greatly enhances the chance of observing
SGRB "orphan" afterglows. Efforts should go in the direction of finding and
identifying such orphan afterglows as counterparts of GW events.Comment: 13 pages, 5 figures, 2 tables. Accepted for publication in Astronomy
& Astrophysics. Figure 5 and angle ranges corrected in revised versio
Adaptive filtering techniques for gravitational wave interferometric data: Removing long-term sinusoidal disturbances and oscillatory transients
It is known by the experience gained from the gravitational wave detector
proto-types that the interferometric output signal will be corrupted by a
significant amount of non-Gaussian noise, large part of it being essentially
composed of long-term sinusoids with slowly varying envelope (such as violin
resonances in the suspensions, or main power harmonics) and short-term ringdown
noise (which may emanate from servo control systems, electronics in a
non-linear state, etc.). Since non-Gaussian noise components make the detection
and estimation of the gravitational wave signature more difficult, a denoising
algorithm based on adaptive filtering techniques (LMS methods) is proposed to
separate and extract them from the stationary and Gaussian background noise.
The strength of the method is that it does not require any precise model on the
observed data: the signals are distinguished on the basis of their
autocorrelation time. We believe that the robustness and simplicity of this
method make it useful for data preparation and for the understanding of the
first interferometric data. We present the detailed structure of the algorithm
and its application to both simulated data and real data from the LIGO 40meter
proto-type.Comment: 16 pages, 9 figures, submitted to Phys. Rev.
Virgo calibration and reconstruction of the gravitational wave strain during VSR1
Virgo is a kilometer-length interferometer for gravitational waves detection
located near Pisa. Its first science run, VSR1, occured from May to October
2007. The aims of the calibration are to measure the detector sensitivity and
to reconstruct the time series of the gravitational wave strain h(t). The
absolute length calibration is based on an original non-linear reconstruction
of the differential arm length variations in free swinging Michelson
configurations. It uses the laser wavelength as length standard. This method is
used to calibrate the frequency dependent response of the Virgo mirror
actuators and derive the detector in-loop response and sensitivity within ~5%.
The principle of the strain reconstruction is highlighted and the h(t)
systematic errors are estimated. A photon calibrator is used to check the sign
of h(t). The reconstructed h(t) during VSR1 is valid from 10 Hz up to 10 kHz
with systematic errors estimated to 6% in amplitude. The phase error is
estimated to be 70 mrad below 1.9 kHz and 6 micro-seconds above.Comment: 8 pages, 8 figures, proceedings of Amaldi 8 conference, to be
published in Journal of Physics Conference Series (JPCS). Second release:
correct typo
Calibration and sensitivity of the Virgo detector during its second science run
The Virgo detector is a kilometer-length interferometer for gravitational
wave detection located near Pisa (Italy). During its second science run (VSR2)
in 2009, six months of data were accumulated with a sensitivity close to its
design. In this paper, the methods used to determine the parameters for
sensitivity estimation and gravitational wave reconstruction are described. The
main quantities to be calibrated are the frequency response of the mirror
actuation and the sensing of the output power. Focus is also put on their
absolute timing. The monitoring of the calibration data as well as the
parameter estimation with independent techniques are discussed to provide an
estimation of the calibration uncertainties. Finally, the estimation of the
Virgo sensitivity in the frequency-domain is described and typical
sensitivities measured during VSR2 are shown.Comment: 30 pages, 23 figures, 1 table. Published in Classical and Quantum
Gravity (CQG), Corrigendum include
Scientific Objectives of Einstein Telescope
The advanced interferometer network will herald a new era in observational
astronomy. There is a very strong science case to go beyond the advanced
detector network and build detectors that operate in a frequency range from 1
Hz-10 kHz, with sensitivity a factor ten better in amplitude. Such detectors
will be able to probe a range of topics in nuclear physics, astronomy,
cosmology and fundamental physics, providing insights into many unsolved
problems in these areas.Comment: 18 pages, 4 figures, Plenary talk given at Amaldi Meeting, July 201
Reconstruction of the gravitational wave signal during the Virgo science runs and independent validation with a photon calibrator
The Virgo detector is a kilometer-scale interferometer for gravitational wave
detection located near Pisa (Italy). About 13 months of data were accumulated
during four science runs (VSR1, VSR2, VSR3 and VSR4) between May 2007 and
September 2011, with increasing sensitivity.
In this paper, the method used to reconstruct, in the range 10 Hz-10 kHz, the
gravitational wave strain time series from the detector signals is
described. The standard consistency checks of the reconstruction are discussed
and used to estimate the systematic uncertainties of the signal as a
function of frequency. Finally, an independent setup, the photon calibrator, is
described and used to validate the reconstructed signal and the
associated uncertainties.
The uncertainties of the time series are estimated to be 8% in
amplitude. The uncertainty of the phase of is 50 mrad at 10 Hz with a
frequency dependence following a delay of 8 s at high frequency. A bias
lower than and depending on the sky direction of the GW is
also present.Comment: 35 pages, 16 figures. Accepted by CQ
Search for Gravitational Wave Bursts from Six Magnetars
Soft gamma repeaters (SGRs) and anomalous X-ray pulsars (AXPs) are thought to be magnetars: neutron stars powered by extreme magnetic fields. These rare objects are characterized by repeated and sometimes spectacular gamma-ray bursts. The burst mechanism might involve crustal fractures and excitation of non-radial modes which would emit gravitational waves (GWs). We present the results of a search for GW bursts from six galactic magnetars that is sensitive to neutron star f-modes, thought to be the most efficient GW emitting oscillatory modes in compact stars. One of them, SGR 0501+4516, is likely similar to 1 kpc from Earth, an order of magnitude closer than magnetars targeted in previous GW searches. A second, AXP 1E 1547.0-5408, gave a burst with an estimated isotropic energy >10(44) erg which is comparable to the giant flares. We find no evidence of GWs associated with a sample of 1279 electromagnetic triggers from six magnetars occurring between 2006 November and 2009 June, in GW data from the LIGO, Virgo, and GEO600 detectors. Our lowest model-dependent GW emission energy upper limits for band-and time-limited white noise bursts in the detector sensitive band, and for f-mode ringdowns (at 1090 Hz), are 3.0 x 10(44)d(1)(2) erg and 1.4 x 10(47)d(1)(2) erg, respectively, where d(1) = d(0501)/1 kpc and d(0501) is the distance to SGR 0501+4516. These limits on GW emission from f-modes are an order of magnitude lower than any previous, and approach the range of electromagnetic energies seen in SGR giant flares for the first time.United States National Science FoundationScience and Technology Facilities Council of the United KingdomMax-Planck-SocietyState of Niedersachsen/GermanyItalian Istituto Nazionale di Fisica NucleareFrench Centre National de la Recherche ScientifiqueAustralian Research CouncilCouncil of Scientific and Industrial Research of IndiaIstituto Nazionale di Fisica Nucleare of ItalySpanish Ministerio de Educacion y CienciaConselleria d'Economia Hisenda i Innovacio of the Govern de les Illes BalearsFoundation for Fundamental Research on Matter supported by the Netherlands Organisation for Scientific ResearchPolish Ministry of Science and Higher EducationFoundation for Polish ScienceRoyal SocietyScottish Funding CouncilScottish Universities Physics AllianceNational Aeronautics and Space Administration NNH07ZDA001-GLASTCarnegie TrustLeverhulme TrustDavid and Lucile Packard FoundationResearch CorporationAlfred P. Sloan FoundationRussian Space AgencyRFBR 09-02-00166aIPN JPL Y503559 (Odyssey), NASA NNG06GH00G, NASA NNX07AM42G, NASA NNX08AC89G (INTEGRAL), NASA NNG06GI896, NASA NNX07AJ65G, NASA NNX08AN23G (Swift), NASA NNX07AR71G (MESSENGER), NASA NNX06AI36G, NASA NNX08AB84G, NASA NNX08AZ85G (Suzaku), NASA NNX09AU03G (Fermi)Astronom
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