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 language||English (US)|
|State||Published - Oct 17 2017|
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