Viewing Angle Dependence of Kilonova Lightcurves from Globally Aspherical Geometries
Abstract
The merger of two neutron stars (NSs) or a black hole (BH) and a neutron star produces a radioactively-powered transient known as a kilonova. The electromagnetic (EM) counterpart to the gravitational wave (GW) event GW170817 was the first observation of a kilonova, and the recent GW detection on 08/14/2019 was likely the first observation of a BH-NS merger. Kilonovae have primarily been modeled with spherically symmetric geometries, though the dynamical ejecta and disk outflow can be considerably anisotropic, an effect that is more pronounced for BH-NS mergers. We study the time-domain signatures of aspherical kilonovae using simple axisymmetric geometries, namely an ellipsoid and a torus. We perform simulations using the time-dependent Monte Carlo radiative transfer code SEDONA. We present the direction-dependent lightcurves of the ejecta, and quantify the systematic uncertainties involved in drawing inferences from a spherical or aspherical model. We provide a simple prescription to estimate the direction-dependent lightcurves of the aspherical ejecta from the lightcurve of the equivalent spherical ejecta (with the same mass and kinetic energy).
- Publication:
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American Astronomical Society Meeting Abstracts #235
- Pub Date:
- January 2020
- Bibcode:
- 2020AAS...23533401D