A neutrinosphere model for kilonova photometry

Models of the electromagnetic emission from a binary neutron star merger are interesting and useful in deducing properties of the merger. We present a unified, physically motivated kilonova model for the UV to IR lightcurves. We develop a neutrinosphere model to parametrize the ejecta composition, and account for ejecta anisotropy and viewing angle effects in producing the observed lightcurves. We are able to describe the data from GW170817, and present fits of the UV to IR lightcurves. Our total inferred ejecta mass of 0.075 solar masses agrees roughly with that inferred by previous models, but the mass ratios of our lanthanide-rich (i.e. “red'') to lanthanide-poor (i.e. “blue'') components is somewhat higher. The velocity of our lanthanide-rich component, 0.27c, is much higher than that inferred by previous models. We also fit blackbodies to the early-time optical photometry, accounting for the blueshift of the expanding ejecta. Our velocity and temperature fits are slower and, for the most part, colder than previous estimates.