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A Hubble constant measurement from superluminal motion of the jet in GW170817

Hotokezaka, K. and Nakar, E. and Gottlieb, O. and Nissanke, S. and Masuda, K. and Hallinan, G. and Mooley, K. P. and Deller, A. T. (2018) A Hubble constant measurement from superluminal motion of the jet in GW170817. . (Submitted)

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The Hubble constant (H_0) measures the current expansion rate of the Universe, and plays a fundamental role in cosmology. Tremendous effort has been dedicated over the past decades to measure H_0. Notably, Planck cosmic microwave background (CMB) and the local Cepheid-supernovae distance ladder measurements determine H_0 with a precision of ∼1% and ∼2% respectively. A 3-σ level of discrepancy exists between the two measurements, for reasons that have yet to be understood. Gravitational wave (GW) sources accompanied by electromagnetic (EM) counterparts offer a completely independent standard siren (the GW analogue of an astronomical standard candle) measurement of H_0, as demonstrated following the discovery of the neutron star merger, GW170817. This measurement does not assume a cosmological model and is independent of a cosmic distance ladder. The first joint analysis of the GW signal from GW170817 and its EM localization led to a measurement of H_0=74^(+16)_(−8) km/s/Mpc (median and symmetric 68% credible interval). In this analysis, the degeneracy in the GW signal between the source distance and the weakly constrained viewing angle dominated the H_0 measurement uncertainty. Recently, Mooley et al. (2018) obtained tight constraints on the viewing angle using high angular resolution imaging of the radio counterpart of GW170817. Here we obtain a significantly improved measurement H_0=68.9^(+4.7)_(−4.6) km/s/Mpc by using these new radio observations, combined with the previous GW and EM data. We estimate that 15 more localized GW170817-like events (comparable signal-to-noise ratio, favorable orientation), having radio images and light curve data, will potentially bring resolution to the tension between the Planck and Cepheid-supernova measurements, as compared to 50-100 GW events without such data.

Item Type:Report or Paper (Discussion Paper)
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URLURL TypeDescription Paper
Hotokezaka, K.0000-0002-2502-3730
Hallinan, G.0000-0002-7083-4049
Mooley, K. P.0000-0002-2557-5180
Additional Information:The authors are grateful to Duncan Brown, Christopher Hirata, Victoria Scowcroft, Peter Shawhan, David Spergel, Hiranya Peiris for useful discussions. We thank the LIGO Scientific Collaboration and Virgo Collaboration for public access to data products. K.H. is supported by Lyman Spitzer Jr. Fellowship at Department of Astrophysical Sciences, Princeton University. E.N. and O.G. are supported by the I-Core center of excellence of the CHE-ISF. SMN is grateful for support from NWO VIDI and TOP Grants of the Innovational Research Incentives Scheme (Vernieuwingsimpuls) financed by the Netherlands Organization for Scientific Research (NWO). The work of K.M. is supported by NASA through the Sagan Fellowship Program executed by the NASA Exoplanet Science Institute, under contract with the California Institute of Technology (Caltech)/Jet Propulsion Laboratory (JPL). GH acknowledges the support of NSF award AST-1654815. A.T.D. is the recipient of an Australian Research Council Future Fellowship (FT150100415). Author Contributions: K.H. carried out MCMC simulations with the synthetic models. E.N. and O.G. derived an analytic model and carried out hydrodynamic simulation to derive constraints on the viewing angle. K.H. and K.M. analyzed the posterior samples and calculated H_0. G.H, K.P.M., A.T.D. provided the input observational data. K.H., E.N., S.N., G.H. wrote the paper. All coauthors discussed the results and provided comments on the manuscript. The authors declare no competing financial interests. Data Availability: MCMC samples are available from the corresponding author on request. Code Availability: The codes used for generating the synthetic light curves are currently being readied for public release. Markov chain Monte Carlo Ensemble sampler: emcee.
Group:Infrared Processing and Analysis Center (IPAC)
Funding AgencyGrant Number
Princeton UniversityUNSPECIFIED
Isreal Science FoundationUNSPECIFIED
Nederlandse Organisatie voor Wetenschappelijk Onderzoek (NWO)UNSPECIFIED
Australian Research CouncilFT150100415
Jansky FellowshipUNSPECIFIED
Record Number:CaltechAUTHORS:20180905-132851528
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:89394
Deposited By: Tony Diaz
Deposited On:05 Sep 2018 20:44
Last Modified:14 May 2019 21:40

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