Second Einstein Telescope Mock Science Challenge : Detection of the GW Stochastic Background from Compact Binary Coalescences

We present the results of the search for an astrophysical gravitational-wave stochastic background during the second Einstein Telescope mock data and science challenge. Assuming that the loudest sources can be detected individually and removed from the data, we show that the residual background can be recovered with an accuracy of $1$ with the standard cross-correlation statistic, after correction of a systematic bias due to the non-isotropy of the sources.Comment: 15 pages, 4 figures, accepted for publication in Physical Review

Astrophysical Sources of Stochastic Gravitational-Wave Background

We review the spectral properties of stochastic backgrounds of astrophysical origin and discuss how they may differ from the primordial contribution by their statistical properties. We show that stochastic searches with the next generation of terrestrial interferometers could put interesting constrains on the physical properties of astrophysical populations, such as the ellipticity and magnetic field of magnetars, or the coalescence rate of compact binaries.Comment: 12 pages, 3 figures,accepted for publication in CQG, GWDAW12 conference proceedings version corrected in comparison published version where we found an error in equation (4

Stochastic Gravitational Wave Background from Coalescing Binary Black Holes

We estimate the stochastic gravitational wave (GW) background signal from the field population of coalescing binary stellar mass black holes (BHs) throughout the Universe. This study is motivated by recent observations of BH-Wolf-Rayet star systems and by new estimates in the metallicity abundances of star forming galaxies that imply BH-BH systems are more common than previously assumed. Using recent analytical results of the inspiral-merger-ringdown waveforms for coalescing binary BH systems, we estimate the resulting stochastic GW background signal. Assuming average quantities for the single source energy emissions, we explore the parameter space of chirp mass and local rate density required for detection by advanced and third generation interferometric GW detectors. For an average chirp mass of 8.7$M_{\odot}$, we find that detection through 3 years of cross-correlation by two advanced detectors will require a rate density, $r_0 \geq 0.5 \rm{Mpc}^{-3} \rm{Myr}^{-1}$. Combining data from multiple pairs of detectors can reduce this limit by up to 40%. Investigating the full parameter space we find that detection could be achieved at rates $r_0 \sim 0.1 \rm{Mpc}^{-3} \rm{Myr}^{-1}$ for populations of coalescing binary BH systems with average chirp masses of $\sim 15M_{\odot}$ which are predicted by recent studies of BH-Wolf-Rayet star systems. While this scenario is at the high end of theoretical estimates, cross-correlation of data by two Einstein Telescopes could detect this signal under the condition $r_0 \geq 10^{-3} \rm{Mpc}^{-3} \rm{Myr}^{-1}$. Such a signal could potentially mask a primordial GW background signal of dimensionless energy density, $\Omega_{\rm{GW}}\sim 10^{-10}$, around the (1--500) Hz frequency range.Comment: 22 pages, 5 figures, 2 tables, Accepted for publication by Ap

Evidence for a dual population of neutron star mergers from short Gamma-Ray Burst observations

Short duration Gamma-Ray Bursts are thought to originate from the coalescence of neutron stars in binary systems. They are detected as a brief ($<$ 2s), intense flash of gamma-ray radiation followed by a weaker, rapidly decreasing afterglow. They are expected to be detected by Advanced LIGO and Virgo when their sensitivity will be low enough. In a recent study we identified a population of short Gamma-Ray Bursts that are intrinsically faint and nearby. Here we provide evidence in favor of the existence of this new population that can hardly be reproduced with a model of field neutron star binary coalescences. We propose that these systems may be produced dynamically in globular clusters, and may result from the merger of a black hole and a neutron star. The advanced LIGO and Virgo observation of a high rate of NSBH mergers compatible with the dynamical formation in globular clusters would be a confirmation of this hypothesis and would enable for the derivation of the mass function of black holes inside globular clusters, as well as the luminosity function of faint short GRBs.Comment: 15 pages, 5 figures, 1 table, submitted to Ap

Searching Gravitational Waves from Pulsars, Using Laser Beam Interferometers

We use recent population synthesis results to investigate the distribution of pulsars in the frequency space, having a gravitational strain high enough to be detected by the future generations of laser beam interferometers. We find that until detectors become able to recover the entire population, the frequency distribution of the 'detectable' population will be very dependent on the detector noise curve. Assuming a mean equatorial deformation $\epsilon =10^{-6}$, the optimal frequency is around 450 Hz for interferometers of the first generation (LIGO or VIRGO) and shifts toward 85 Hz for advanced detectors. An interesting result for future detection stategies is the significant narrowing of the distribution when improving the sensitivity: with an advanced detector, it is possible to have 90% of detection probability while exploring less than 20% of the parameter space (7.5% in the case of $\epsilon =10^{-5}$). In addition, we show that in most cases the spindown of 'detectable' pulsars represents a period shift of less than a tens of nanoseconds after one year of observation, making them easier to follow in the frequency space.Comment: 5 pages, 3 figures accepted for publication in Astronomy & Astrophysic

Stochastic background from extra-galactic double neutron stars

We present Monte Carlo simulations of the extra galactic population of inspiralling double neutron stars, and estimate its contribution to the astrophysical gravitational wave background, in the frequency range of ground based interferometers, corresponding to the last thousand seconds before the last stable orbit when more than 96 percent of the signal is released. We show that sources at redshift z>0.5 contribute to a truly continuous background which may be detected by correlating third generation interferometers.Comment: 13 pages, 7 figures - proceeding of a talk given at the 11th GWDAW, to appear in CQ

Stochastic backgrounds of gravitational waves from extragalactic sources

Astrophysical sources emit gravitational waves in a large variety of processes occurred since the beginning of star and galaxy formation. These waves permeate our high redshift Universe, and form a background which is the result of the superposition of different components, each associated to a specific astrophysical process. Each component has different spectral properties and features that it is important to investigate in view of a possible, future detection. In this contribution, we will review recent theoretical predictions for backgrounds produced by extragalactic sources and discuss their detectability with current and future gravitational wave observatories.Comment: 10 pages, 9 figures, proceedings of the GWDAW 10 Conference, submitted to Class. & Quantum Gra

Gravitational Wave Background from Magnetars

We investigate the gravitational wave background produced by magnetars. The statistical properties of these highly magnetized stars were derived by population synthesis methods and assumed to be also representative of extragalactic objects. The adopted ellipticity was calculated from relativistic models using equations of state and assumptions concerning the distribution of currents in the neutron star interior. The maximum amplitude occurs around 1.2 kHz, corresponding to $\Omega_{gw} \sim 10^{-9}$ for a type I superconducting neutron star model. The expected signal is a continuous background that could mask the cosmological contribution produced in the early stage of the Universe.Comment: accepted for publication in A&A; 17 pages, 7 figures; formula 21 has been corrected with respect to the published versio

Quark core formation in spinning-down pulsars

Pulsars spin-down due to magnetic torque reducing its radius and increasing the central energy density. Some pulsar which are born with central densities close to the critical value of quark deconfinement may undergo a phase transition and structural re-arrengement. This process may excite oscillation modes and emmit gravitational waves. We determine the rate of quark core formation in neutron stars using a realistic population synthesis code.Comment: Proceedings of the 2nd International Workshop on Astronomy and Relativistic Astrophysics, to appear in IJMP