2015/04/30 by Lindley Lentati, Stephen R. Taylor, Chiara M. F. Mingarelli +33 · 1 citation
Physics and Astronomy · #astro-ph.CO #astro-ph.IM
paper · pdf · doi:10.1093/mnras/stv1538
published as Monthly Notices of the Royal Astronomical Society 2015 453 (3): 2576-2598 · 24 pages, 5 tables, 17 figures
arxiv created 2015/09/09 · arxiv updated 2015/09/10
We 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. Performing a Bayesian analysis, we fit simultaneously for the intrinsic noise parameters for each pulsar, along with common correlated signals including clock, and Solar System ephemeris errors, obtaining a robust 95% upper limit on the dimensionless strain amplitude A of the background of A<3.0× 10-15 at a reference frequency of 1\mathrmyr-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 Ωgw(f)h2 < 1.1×10-9 at 2.8 nHz. We also present limits on the correlated power spectrum at a series of discrete frequencies, and show that our sensitivity to a fiducial isotropic GWB is highest at a frequency of ∼ 5×10-9~Hz. Finally we discuss the implications of our analysis for the astrophysics of supermassive black hole binaries, and present 95% upper limits on the string tension, Gμ/c2, 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 Gμ/c2<1.3×10-7, identical to that set by the \it Planck Collaboration, when combining \it Planck and high-ℓ Cosmic Microwave Background data from other experiments. For a stochastic relic background we set a limit of Ωrelicgw(f)h2<1.2 ×10-9, a factor of 9 improvement over the most stringent limits previously set by a pulsar timing array.