A standard siren measurement of the Hubble constant using GW170817 and the latest observations of the electromagnetic counterpart afterglow

We present a new constraint on the Hubble constant $H_0$ using the latest measurements of the electromagnetic counterpart to the gravitational wave (GW) event GW170817. We use the latest optical, X-ray and radio observations of the afterglow up to $\sim 3.5$ years after the GW detection, and properly take into account the impact of the host galaxy peculiar velocity. We find $75.46^{+5.34}_{-5.39}$ km s$^{-1}$ Mpc$^{-1}$ (68\% Credible Interval), a $\sim7\%$ precision measurement, which is a significant improvement compared to the $14\%$ precision of the first standard siren measurement. Our result is consistent within $1\sigma$ with the Cepheid-anchored Supernova and within $1.5 \sigma$ with the Cosmic Microwave Background measurements of the Hubble constant. We also explore the impact of the various assumptions made when fitting for the afterglow on the Hubble constant estimate.