On August 17, 2017, the Advanced LIGO and Advanced Virgo gravitational-wave detectors observed a
low-mass compact binary inspiral. The initial sky localization of the source of the gravitational-wave signal,
GW170817, allowed electromagnetic observatories to identify NGC 4993 as the host galaxy. In this work, we
improve initial estimates of the binary’s properties, including component masses, spins, and tidal parameters,
using the known source location, improved modeling, and recalibrated Virgo data. We extend the range of
gravitational-wave frequencies considered down to 23 Hz, compared to 30 Hz in the initial analysis. We also
compare results inferred using several signal models, which are more accurate and incorporate additional
physical effects as compared to the initial analysis. We improve the localization of the gravitational-wave
source to a 90% credible region of 16 deg2. We find tighter constraints on the masses, spins, and tidal
parameters, and continue to find no evidence for nonzero component spins. The component masses are
inferred to lie between 1.00 and 1.89 M⊙ when allowing for large component spins, and to lie between 1.16
and 1.60 M⊙ (with a total mass 2.73þ0.04 −0.01 M⊙) when the spins are restricted to be within the range observed in
Galactic binary neutron stars. Using a precessing model and allowing for large component spins, we
constrain the dimensionless spins of the components to be less than 0.50 for the primary and 0.61 for the
secondary. Under minimal assumptions about the nature of the compact objects, our constraints for the tidal
deformability parameter Λ˜ are (0,630) when we allow for large component spins, and 300þ420
−230 (using a 90%
highest posterior density interval) when restricting the magnitude of the component spins, ruling out several
equation-of-state models at the 90% credible level. Finally, with LIGO and GEO600 data, we use a Bayesian
analysis to place upper limits on the amplitude and spectral energy density of a possible postmerger signal.