A Standard Siren Cosmological Measurement from the Potential GW190521
  Electromagnetic Counterpart ZTF19abanrhr
  The identification of the electromagnetic counterpart candidate ZTF19abanrhr
to the binary black hole merger GW190521 opens the possibility to infer
cosmological parameters from this standard siren with a uniquely identified
host galaxy. The distant merger allows for cosmological inference beyond the
Hubble constant. Here we show that the three-dimensional spatial location of
ZTF19abanrhr calculated from the electromagnetic data remains consistent with
the updated sky localization of GW190521 provided by the LIGO-Virgo
Collaboration. If ZTF19abanrhr is associated with the GW190521 merger and
assuming a flat wCDM model we find that $H_0 =48^{+24}_{-10}$ km/s/Mpc,
$\Omega_m =0.39^{+0.38}_{-0.29}$, and $w_0 = -1.29^{+0.63}_{-0.50}$ (median and
68% credible interval). If we use the Hubble constant value inferred from
another gravitational-wave event, GW170817, as a prior for our analysis,
together with assumption of a flat ${\Lambda}$CDM and the model-independent
constraint on the physical matter density ${\omega}_m$ from Planck, we find
$H_0 = 69.1^{8.7}_{-6.0}$ km/s/Mpc.
