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Are we there yet? Time to detection of nanohertz gravitational waves based on pulsar-timing array limits

Taylor, S. R. and Vallisneri, M. and Ellis, J. A. and Mingarelli, C. M. F. and Lazio, T. J. W. and van Haasteren, R. (2016) Are we there yet? Time to detection of nanohertz gravitational waves based on pulsar-timing array limits. Astrophysical Journal Letters, 819 (1). Art. No. L6. ISSN 2041-8205.

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Decade-long timing observations of arrays of millisecond pulsars have placed highly constraining upper limits on the amplitude of the nanohertz gravitational-wave stochastic signal from the mergers of supermassive black hole binaries (~10^(−15) strain at f = 1 yr^(−1)). These limits suggest that binary merger rates have been overestimated, or that environmental influences from nuclear gas or stars accelerate orbital decay, reducing the gravitational-wave signal at the lowest, most sensitive frequencies. This prompts the question whether nanohertz gravitational waves (GWs) are likely to be detected in the near future. In this Letter, we answer this question quantitatively using simple statistical estimates, deriving the range of true signal amplitudes that are compatible with current upper limits, and computing expected detection probabilities as a function of observation time. We conclude that small arrays consisting of the pulsars with the least timing noise, which yield the tightest upper limits, have discouraging prospects of making a detection in the next two decades. By contrast, we find large arrays are crucial to detection because the quadrupolar spatial correlations induced by GWs can be well sampled by many pulsar pairs. Indeed, timing programs that monitor a large and expanding set of pulsars have an ~80% probability of detecting GWs within the next 10 years, under assumptions on merger rates and environmental influences ranging from optimistic to conservative. Even in the extreme case where 90% of binaries stall before merger and environmental coupling effects diminish low-frequency gravitational-wave power, detection is delayed by at most a few years.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Taylor, S. R.0000-0003-0264-1453
Vallisneri, M.0000-0002-4162-0033
Mingarelli, C. M. F.0000-0002-4307-1322
Lazio, T. J. W.0000-0002-3873-5497
van Haasteren, R.0000-0002-6428-2620
Additional Information:© 2016 American Astronomical Society. Received 2015 November 18; accepted 2016 January 21; published 2016 February 23. It is our pleasure to thank Pablo Rosado, Alberto Sesana, Jonathan Gair, Lindley Lentati, Sarah Burke-Spolaor, Xavier Siemens, Maura McLaughlin, Joseph Romano, and Michael Kramer for very useful suggestions. We also thank the full NANOGrav collaboration for their comments and remarks. S.R.T. was supported by an appointment to the NASA Postdoctoral Program at the Jet Propulsion Laboratory, administered by Oak Ridge Associated Universities through a contract with NASA. M.V. acknowledges support from the JPL RTD program. J.A.E. and R.v.H. acknowledge support by NASA through Einstein Fellowship grants PF4-150120 and PF3-140116, respectively. C.M.F.M. was supported by a Marie Curie International Outgoing Fellowship within the European Union Seventh Framework Programme. This work was supported in part by National Science Foundation Physics Frontier Center award No. 1430284 and by grant PHYS-1066293 and the hospitality of the Aspen Center for Physics. This research was performed at the Jet Propulsion Laboratory, under contract with the National Aeronautics and Space Administration.
Funding AgencyGrant Number
JPL/NASA Postdoctoral ProgramUNSPECIFIED
NASA Oak Ridge Associated UniversitiesUNSPECIFIED
JPL Research and Technology Development FundUNSPECIFIED
NASA Einstein FellowshipPF4-150120
NASA Einstein FellowshipPF3-140116
Marie Curie International Outgoing FellowshipUNSPECIFIED
Subject Keywords:gravitational waves; methods: data analysis; pulsars: general
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Other Numbering System NameOther Numbering System ID
Space Radiation Laboratory2016-34
Issue or Number:1
Record Number:CaltechAUTHORS:20160226-073845969
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Official Citation:S. R. Taylor et al 2016 ApJ 819 L6
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:64786
Deposited By: Ruth Sustaita
Deposited On:29 Feb 2016 20:27
Last Modified:09 Mar 2020 13:19

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