UC Berkeley

The merger of two neutron stars produces a neutron-rich outflow of >0.01 solar masses. This ejecta is a prime site for r-process nucleosynthesis, which will produce a range of radioactive heavy nuclei. Within a second of merger, an accretion disc forms around the central remnant. Material from this disc accretes onto the central compact object, launching a relativistic jet. The disc is also the source of a mildly-relativistic radioactive wind. Heating by r-process decays can accelerate accelerate portions of this wind by ~0.1c. Within a few hours, emission from the radioactive material gives rise to an ultraviolet, optical, and infrared transient: a kilonova. These ejecta are not expected to be spherically symmetric, so the emission will depend on the multi-dimensional ejecta structure as well as the viewing angle of the observer. Calculating this emission requires solving the time-dependent equation of radiation transport. To do so, I use Sedona, a parallel multi-dimensional, multi-frequency Monte Carlo radiation transport code. I analyze the parallel structure and performance of Sedona on modern supercomputers and discuss the performance and usability improvements I have made to the code. I use the endstates of a suite of 2D relativistic hydrodynamic simulations of jet-ejecta interaction as initial conditions for Sedona calculations, producing viewing angle-dependent light curves and spectra starting at 1.5 h after merger. I find that on this time-scale, jet shock heating does not affect the kilonova emission for the jet parameters surveyed. However, the jet disruption to the density structure of the ejecta does change the light curves. The jet carves a channel into the otherwise spheroidal ejecta, revealing the hot, inner regions, and making polar emission brighter and bluer. The winds launched from post-merger accretion discs are also aspherical. I continue a 3D general relativistic magnetohydrodynamic simulation of a disc wind in 2D hydrodynamics, and follow it until the flow is self-similar. I find that the inclusion of r-process heating doubles the mass-weighted median velocity, making the light curves brighter and bluer at ~1 d post-merger.