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We present three-dimensional radiative transfer calculations for the ejectafrom a neutron star merger that include line-by-line opacities for tens ofmillions of bound-bound transitions, composition from an r-process nuclearnetwork, and time-dependent thermalization of decay products from individual$\alpha$ and $\beta^-$ decay reactions. In contrast to expansion opacities andother wavelength-binned treatments, a line-by-line treatment enables us includefluorescence effects and associate spectral features with the emitting andabsorbing lines of individual elements. We find variations in the syntheticobservables with both the polar and azimuthal viewing angles. The spectraexhibit blended features with strong interactions by Ce III, Sr II, Y II, andZr II that vary with time and viewing direction. We demonstrate the importanceof wavelength-calibration of atomic data using a model with calibrated Sr, Y,and Zr data, and find major differences in the resulting spectra, including abetter agreement with AT2017gfo. The synthetic spectra for near-polarinclination show a feature at around 8000 A, similar to AT2017gfo. However,they evolve on a more rapid timescale, likely due to the low ejecta mass (0.005M$_\odot$) as we take into account only the early ejecta. The comparativelyfeatureless spectra for equatorial observers gives a tentative prediction thatfuture observations of edge-on kilonovae will appear substantially differentfrom AT2017gfo. We also show that 1D models obtained by spherically averagingthe 3D ejecta lead to dramatically different direction-integrated luminositiesand spectra compared to full 3D calculations.

Self-consistent 3D radiative transfer for kilonovae: directional spectra from merger simulations