Improved constraints on H0 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

Research output: Contribution to journalArticlepeer-review


The luminosity distance measurement of GW170817 derived from GW analysis in Abbott et al. (2017) (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 broad-band 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 1048 erg < Ek ≤ 3 ×1050 erg propagating into an environment with density n - 10−2 − 10−4 cm−3, with preference for wider jets (opening angle θj = 15). For these jets, our modeling indicates an off-axis angle θobs - 25 − 50. We combine our constraints on θobs with the joint distance-inclination constraint from LIGO. Using the same - 170 km/sec peculiar velocity uncertainty assumed in A17:H0 but with an inclination constraint from the afterglow data, we get a value of H0 =74.0 ±117..55 km/s/Mpc, which is higher than the value of H0 =70.0 ±128..00 km/s/Mpc found in A17:H0. Further, using a more realistic peculiar velocity uncertainty of 250 km/sec derived from previous work, we find H0 =75.5 ±119..66 km/s/Mpc for H0 from this system. We note that this is in modestly better agreement with the local distance ladder than the Planck CMB, though a significant such discrimination will require - 50 such events. Future measurements at t > 100 days of the X-ray and radio emission will lead to tighter constraints.

Original languageEnglish (US)
JournalUnknown Journal
StatePublished - Oct 17 2017

ASJC Scopus subject areas

  • General

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