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From bright binaries to bumpy backgrounds: Mapping realistic gravitational wave skies with pulsar-timing arrays

Taylor, Stephen R. and van Haasteren, Rutger and Sesana, Alberto (2020) From bright binaries to bumpy backgrounds: Mapping realistic gravitational wave skies with pulsar-timing arrays. Physical Review D, 102 (8). Art. No. 084039. ISSN 2470-0010. doi:10.1103/PhysRevD.102.084039.

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Within the next several years, pulsar-timing array programs will likely usher in the next era of gravitational-wave astronomy through the detection of a stochastic background of nanohertz-frequency gravitational waves, originating from a cosmological population of inspiraling supermassive binary black holes. While the source positions will likely be isotropic to a good approximation, the gravitational-wave angular power distribution will be anisotropic, with the most massive and/or nearby binaries producing signals that may resound above the background. We study such a realistic angular power distribution, developing fast and accurate sky-mapping strategies to localize pixels and extended regions of excess power while simultaneously modeling the background signal from the less massive and more distant ensemble. We find that power anisotropy will be challenging to discriminate from isotropy for realistic gravitational-wave skies, requiring SNR >10 in order to favor anisotropy with 10:1 posterior odds in our case study. Amongst our techniques, modeling the population signal with multiple point sources in addition to an isotropic background provides the most physically motivated and easily interpreted maps, while spherical-harmonic modeling of the square-root power distribution, P(Ω)^(1/2), performs best in discriminating from overall isotropy. Our techniques are modular and easily incorporated into existing pulsar-timing array analysis pipelines.

Item Type:Article
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URLURL TypeDescription Paper ItemCode
Taylor, Stephen R.0000-0003-0264-1453
van Haasteren, Rutger0000-0002-6428-2620
Additional Information:© 2020 American Physical Society. Received 9 June 2020; accepted 25 August 2020; published 15 October 2020. We thank Sharan Banagiri, Vuk Mandic, Joe Romano, Eric Thrane, Ethan Payne, and Marc Kamionkowski, as well as colleagues in the NANOGrav collaboration and the International Pulsar Timing Array, for useful discussions. Much of this work was performed at the Jet Propulsion Laboratory, where S. R. T. was supported by appointment to the NASA Postdoctoral Program, administered by Oak Ridge Associated Universities and the Universities Space Research Association through a contract with NASA. S. R. T. was also supported by the NANOGrav NSF Physics Frontier Center Award No. 1430284. This work was supported in part by National Science Foundation Grant No. PHYS-1066293 and by the hospitality of the Aspen Center for Physics. A. S. is supported by the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation program ERC-2018-COG under Grant Agreement No. 818691 (B Massive). A majority of the computational work was performed on the Nemo cluster at UWM supported by NSF Grant No. 0923409. Some of the results in this paper have been derived using the healpix [106] package.
Funding AgencyGrant Number
NASA Postdoctoral ProgramUNSPECIFIED
European Research Council (ERC)818691
Issue or Number:8
Record Number:CaltechAUTHORS:20201019-072046979
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:106130
Deposited By: Tony Diaz
Deposited On:20 Oct 2020 15:51
Last Modified:16 Nov 2021 18:50

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