Constraining the Observer Angle of the Kilonova AT2017gfo Associated with GW170817: Implications for the Hubble Constant
Abstract
There is a strong degeneracy between the luminosity distance (D _{ L }) and the observer viewing angle (θ _{obs}; hereafter viewing angle) of the gravitational wave (GW) source with an electromagnetic counterpart, GW170817. Here, for the first time, we present independent constraints on {θ }_{obs}}={32.5}_{9.7}^{^\circ +11.7} from broadband photometry of the kilonova (kN) AT2017gfo associated with GW170817. These constraints are consistent with independent results presented in the literature using the associated gammaray burst GRB 170817A. Combining the constraints on θ _{obs} with the GW data, we find an improvement of 24% on H _{0}. The observer angle constraints are insensitive to other model parameters, e.g., the ejecta mass, the halfopening angle of the lanthaniderich region and the temperature. A broad wavelength coverage extending to the nearinfrared is helpful to robustly constrain θ _{obs}. While the improvement on H _{0} presented here is smaller than the one from high angular resolution imaging of the radio counterpart of GW170817, kN observations are significantly more feasible at the typical distances of such events from current and future LIGO─Virgo collaboration observing runs (D _{ L } ∼ 100 Mpc). Our results are insensitive to the assumption of the peculiar velocity of the kN host galaxy.
 Publication:

The Astrophysical Journal
 Pub Date:
 January 2020
 DOI:
 10.3847/15384357/ab5799
 arXiv:
 arXiv:1909.13810
 Bibcode:
 2020ApJ...888...67D
 Keywords:

 Hubble constant;
 Cosmological parameters;
 Radiative transfer;
 Gravitational waves;
 Astrophysics  High Energy Astrophysical Phenomena
 EPrint:
 7 pages