2017/10/19 by C. Guidorzi, R. Margutti, D. Brout +17 · 1 citation
Physics and Astronomy · #astro-ph.CO
paper · pdf · doi:10.3847/2041-8213/aaa009
Submitted to ApJL. Comments Welcome. Revised uncertainties in v2
arxiv created 2017/10/19 · arxiv updated 2017/12/27
The luminosity distance measurement of GW170817 derived from GW analysis in Abbott et al. 2017 (here, 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 \rmerg<Ek≤ 3× 1050 \rmerg propagating into an environment with density n∼10-2-10-4 \rmcm-3, with preference for wider jets (opening angle θj=15 deg). For these jets, our modeling indicates an off-axis angle θ\rm obs∼25-50 deg. We combine our constraints on θ\rm obs 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 ± (11.5)/(7.5) km/s/Mpc, which is higher than the value of H0=70.0 ± (12.0)/(8.0) 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 ± (11.6)/(9.6) 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.