Axisymmetric Radiative Transfer Models of Kilonovae
Abstract
The detailed observations of GW170817 proved for the first time directly that neutron star mergers are a major production site of heavy elements. The observations could be fit by a number of simulations that qualitatively agree, but can quantitatively differ (e.g. in total rprocess mass) by an order of magnitude. We categorize kilonova ejecta into several typical morphologies motivated by numerical simulations, and apply a radiative transfer Monte Carlo code to study how the geometric distribution of the ejecta shapes the emitted radiation. We find major impacts on both spectra and light curves. The peak bolometric luminosity can vary by two orders of magnitude and the timing of its peak by a factor of five. These findings provide the crucial implication that the ejecta masses inferred from observations are uncertain by at least an order of magnitude. Mixed twocomponent models with lanthaniderich ejecta are particularly sensitive to geometric distribution. A subset of mixed models shows very strong viewing angle dependence due to lanthanide "curtaining", which persists even if the relative mass of lanthaniderich component is small. The angular dependence is weak in the rest of our models, but different geometric combinations of the two components lead to a highly diverse set of light curves. We identify geometrydependent P Cygni features in late spectra that directly map out strong lines in the simulated opacity of neodymium, which can help to constrain the ejecta geometry and to directly probe the rprocess abundances.
 Publication:

arXiv eprints
 Pub Date:
 March 2020
 arXiv:
 arXiv:2004.00102
 Bibcode:
 2020arXiv200400102K
 Keywords:

 Astrophysics  High Energy Astrophysical Phenomena
 EPrint:
 21 pages, 17 figures: submitted to ApJ