Journal
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
Volume 453, Issue 3, Pages 2576-2598Publisher
OXFORD UNIV PRESS
DOI: 10.1093/mnras/stv1538
Keywords
gravitational waves; methods: data analysis; pulsars: general
Categories
Funding
- European Research Council to implement the Large European Array for Pulsars (LEAP)
- 'Programme National de Cosmologie and Galaxies' (PNCG) of CNRS/INSU, France
- STFC in the UK
- Netherlands Foundation for Scientific Research NWO
- Higher Education Funding Council for England
- Science and Technology Facilities Council
- NSF under MRI-R2 award [PHY-0960291]
- Sherman Fairchild Foundation
- Junior Research Fellowship at Trinity Hall College, Cambridge University
- NASA Postdoctoral Program at the Jet Propulsion Laboratory
- NASA
- Marie Curie International Outgoing Fellowship within the 7th European Community Framework Programme
- Royal Society
- NWO Vidi fellowship (PI JWTH)
- International Max Planck Research School Bonn/Cologne and the Bonn-Cologne Graduate School
- National Natural Science Foundation of China [11373011]
- NASA Einstein Fellowship [PF3-140116]
- NWO Vidi fellowship
- ERC Starting Grant 'DRAG-NET' [337062]
- International Max Planck Research School Bonn/Cologne
- European Research Council for the ERC Synergy Grant BlackHoleCam [610058]
- Alexander von Humboldt Foundation
- STFC [ST/K000845/1, ST/L000768/1] Funding Source: UKRI
- Science and Technology Facilities Council [ST/L000768/1] Funding Source: researchfish
- European Research Council (ERC) [337062] Funding Source: European Research Council (ERC)
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We present new limits on an isotropic stochastic gravitational-wave background (GWB) using a six pulsar data set 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 per cent upper limit on the dimensionless strain amplitude A of the background of A < 3.0 x 10(-15) at a reference frequency of 1 yr(-1) and a spectral index of 13/3, corresponding to a background from inspiralling supermassive black hole binaries, constraining the GW energy density to Omega(gw)(f)h(2) < 1.1 x 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 similar to 5 x 10(-9) Hz. Finally, we discuss the implications of our analysis for the astrophysics of supermassive black hole binaries, and present 95 per cent upper limits on the string tension, G mu/c(2), characterizing 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 G mu/c(2) < 1.3x10(-7), identical to that set by the Planck Collaboration, when combining Planck and high-l cosmic microwave background data from other experiments. For a stochastic relic background, we set a limit of Omega(relic)(gw)(f)h(2) < 1.2 x 10(-9), a factor of 9 improvement over the most stringent limits previously set by a pulsar timing array.
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