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29 March 2024
 
  » arxiv » 1504.3692

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European Pulsar Timing Array Limits On An Isotropic Stochastic Gravitational-Wave Background
Lindley Lentati ; Stephen R. Taylor ; Chiara M. F. Mingarelli ; Alberto Sesana ; Sotiris A. Sanidas ; Alberto Vecchio ; R. Nicolas Caballero ; K. J. Lee ; Rutger van Haasteren ; Stanislav Babak ; Cees G. Bassa ; Patrick Brem ; Marta Burgay ; David J. Champion ; Ismael Cognard ; Gregory Desvignes ; Jonathon R. Gair ; Lucas Guillemot ; Jason W. T. Hessels ; Gemma H. Janssen ; Ramesh Karuppusamy ; Michael Kramer ; Antoine Lassus ; Patrick Lazarus ; Kuo Liu ; Stefan Osłowski ; Delphine Perrodin ; Antoine Petiteau ; Andrea Possenti ; Mark B. Purver ; Pablo A. Rosado ; Roy Smits ; Ben Stappers ; Gilles Theureau ; Caterina Tiburzi ; Joris P. W. Verbiest ;
Date 14 Apr 2015
AbstractWe present new limits on an isotropic stochastic gravitational-wave background (GWB) using a six pulsar dataset spanning 18 yr of observations from the 2015 European Pulsar Timing Array data release (Desvignes et al. in prep.). Performing a Bayesian analysis, we fit simultaneously for the intrinsic noise parameters for each pulsar in this dataset, along with common correlated signals including clock, and Solar System ephemeris errors to obtain a robust 95$\%$ upper limit on the dimensionless strain amplitude $A$ of the background of $A<3.0 imes 10^{-15}$ at a reference frequency of $1mathrm{yr^{-1}}$ and a spectral index of $13/3$, corresponding to a background from inspiralling super-massive black hole binaries, constraining the GW energy density to $Omega_mathrm{gw}(f)h^2 < 3.6 imes10^{-10}$ at 2.8 nHz. We show that performing such an analysis when fixing the intrinsic noise parameters for the individual pulsars leads to an erroneously stringent upper limit, by a factor $sim 1.7$. We obtain a difference in the logarithm of the Bayesian evidence between models that include either a correlated background, or uncorrelated common red noise of $-1.0 pm 0.5$, indicating no support for the presence of a correlated GWB in this dataset. We discuss the implications of our analysis for the astrophysics of supermassive black hole binaries, and present 95$\%$ upper limits on the string tension, $Gmu/c^2$, characterising a background produced by a cosmic string network for a set of possible scenarios, and for a stochastic relic GWB. For a Nambu-Goto field theory cosmic string network, we set a limit $Gmu/c^2<1.3 imes10^{-7}$, identical to that set by the Planck Collaboration, combining Planck and high-$ell$ Cosmic Microwave Background data from other experiments. (Abridged)
Source arXiv, 1504.3692
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