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 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. ₃₉^+5. 34 km s^-1 Mpc^-1 (68% credible interval), a 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 with the cepheid-anchored supernova and within 1. 5 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.