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 H0 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 similar to 3.5 years after the GW detection, and properly take into account the impact of the host galaxy peculiar velocity. We find 75.46 thorn 5.34 -5.39 km s-1 Mpc-1 (68% credible interval), a similar to 7% 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 cepheidanchored 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.