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Two years after its first scientific run, Virgo is about to start a new data taking campaign, jointly with the LIGO detectors. For this year's run, upgrades of the detector and intense commissioning efforts have been made to further increase the performances of the detectors. This presentation aims at reviewing the recent results and their astrophysical consequences. We also discuss the expected improvements in sensitivity, with the upcoming run and with the future Advanced Virgo detector, and their impact on the detection of gravitational waves.
In 2011, the Virgo gravitational wave (GW) detector will definitively end its science program following the shut-down of the LIGO detectors the year before. The years to come will be devoted to the development and installation of second generation detectors. It is the opportune time to review what has been learned from the GW searches in the kilometric interferometers data. Since 2007, data have been collected by the LIGO and Virgo detectors. Analyses have been developed and performed jointly by the two collaborations. Though no detection has been made so far, meaningful upper limits have been set on the astrophysics of the sources and on the rate of GW events. This paper will focus on the transient GW searches performed over the last 3 years. This includes the GW produced by compact binary systems, supernovae core collapse, pulsar glit...
Cosmic strings are linear topological defects which are expected to form during symmetry-breaking phase transitions in the early universe. In addition, some inflation models based on string theory predict that fundamental strings and D-strings could grow to cosmic scales and constitute a network of cosmic superstrings. When forming loops, cosmic strings radiate energy through bursts of gravitational waves in the presence of cuspy features. This mechanism represents one of the most promising observational signatures to detect the existence of cosmic strings. The sensitivity of ground-based gravitational-wave detectors LIGO and Virgo allows us to explore an unconstrained region of the cosmic string parameter space. After reviewing the cosmic string models and the targeted gravitational-wave signals, we present the search for cosmic string...
Two simulations of the seasonal variation of the global atmospheric CO2 distribution are obtained by combining an atmospheric transport model, two parameterizations of soil heterotrophic respiration (SHR), and a mechanistic model of carbon assimilation in the biosphere (CARAIB) that estimates the net primary production (NPP) of continental vegetation. The steady state hypothesis of the biosphere allows the spatial distribution and the global content of the soil carbon to be expressed as a function of the root fractions of soil respiration under forested and herbaceous vegetation covers. The sensitivity of the modeled CO2 signal to the wind field does not exceed the observed interannual variability. The influence of the various vegetation zones is quantified by the Fourier analysis of the modeled atmospheric signal. In the northern hemi...
Performance of gravitational wave (GW) detectors can be characterized by several figures of merit (FOMs) which are used to guide the detector's commissioning and operations, and to gauge astrophysical sensitivity. One key FOM is the range in Mpc, averaged over orientation and sky location, at which a GW signal from binary neutron star inspiral and coalescence would have a signal-to-noise ratio (SNR) of 8 in a single detector. This fixed-SNR approach does not accurately reflect the effects of transient noise (glitches), which can severely limit the detectability of transient GW signals expected from a variety of astrophysical sources. We propose a FOM based instead on a fixed false-alarm probability (FAP). This is intended to give a more realistic estimate of the detectable GW transient range including the effect of glitches. Our approa...
Time shifting the output of gravitational wave detectors operating in coincidence is a convenient way of estimating the background in a search for short-duration signals. In this paper, we show how non-stationary data affect the background estimation precision. We present a method of measuring the fluctuations of the data and computing its effects on a coincident search. In particular, we show that for fluctuations of moderate amplitude, time slides larger than the fluctuation time scales can be used. We also recall how the false alarm variance saturates with the number of time shifts.
Performance of gravitational wave (GW) detectors can be characterized by several figures of merit (FOMs) which are used to guide the detector's commissioning and operations, and to gauge astrophysical sensitivity. One key FOM is the range in Mpc, averaged over orientation and sky location, at which a GW signal from binary neutron star inspiral and coalescence would have a signal-to-noise ratio (SNR) of 8 in a single detector. This fixed-SNR approach does not accurately reflect the effects of transient noise (glitches), which can severely limit the detectability of transient GW signals expected from a variety of astrophysical sources. We propose a FOM based instead on a fixed false-alarm probability (FAP). This is intended to give a more realistic estimate of the detectable GW transient range including the effect of glitches. Our approa...
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