Improved Constraints on H 0 from a Combined Analysis of Gravitational-wave and Electromagnetic Emission from GW170817

C. Guidorzi, R. Margutti, D. Brout, D. Scolnic, W. Fong, K. D. Alexander, P. S. Cowperthwaite, J. Annis, E. Berger, P. K. Blanchard, R. Chornock, D. L. Coppejans, T. Eftekhari, J. A. Frieman, D. Huterer, M. Nicholl, M. Soares-Santos, G. Terreran, V. A. Villar, P. K.G. Williams

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The luminosity distance measurement of GW170817 derived from gravitational-wave analysis in Abbott et al. (2017a, hereafter A17:H0) is highly correlated with the measured inclination of the NS-NS system. To improve the precision of the distance measurement, we attempt to constrain the inclination by modeling the broadband X-ray-to-radio emission from GW170817, which is dominated by the interaction of the jet with the environment. We update our previous analysis and we consider the radio and X-ray data obtained at t < 40 days since merger. We find that the afterglow emission from GW170817 is consistent with an off-axis relativistic jet with energy E k ∼ 1048 -3 1050 erg propagating into an environment with density n ∼ 10-2-10-4 cm-3, with preference for wider jets (opening angle θ j = 15°). For these jets, our modeling indicates an off-axis angle θ obs ∼ 25°-50°. We combine our constraints on θ obs with the joint distance-inclination constraint from LIGO. Using the same ∼170 km s-1 peculiar velocity uncertainty assumed in A17:H0 but with an inclination constraint from the afterglow data, we get a value of km s-1 Mpc-1, which is higher than the value of km s-1 Mpc-1 found in A17:H0. Further, using a more realistic peculiar velocity uncertainty of 250 km s-1 derived from previous work, we find km s-1 Mpc-1 for H 0 from this system. This is in modestly better agreement with the local distance ladder than the Planck cosmic microwave background, though such a significant discrimination will require ∼50 such events. Measurements at t > 100 days of the X-ray and radio emission will lead to tighter constraints.

Original languageEnglish (US)
Article numberL36
JournalAstrophysical Journal Letters
Issue number2
StatePublished - Dec 20 2017

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


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