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Astrophysics, High Energy Astrophysical Phenomena, astro-ph.HE
Abstract:
A merger of binary neutron stars creates heavy unstable elements whose
radioactive decay produces a thermal emission known as a kilonova. In this
paper, we predict the photometric and polarimetric behaviour of this emission
by performing 3-D Monte Carlo radiative transfer simulations. In particular, we
choose three hydrodynamical models for merger ejecta, two including jets with
different luminosities and one without a jet structure, to help decipher the
impact of jets on the light curve and polarimetric behaviour. In terms of
photometry, we find distinct color evolutions across the three models. Models
without a jet show the highest variation in light curves for different viewing
angles. In contrast, to previous studies, we find models with a jet to produce
fainter kilonovae when viewed from orientations close to the jet axis, compared
to a model without a jet. In terms of polarimetry, we predict relatively low
levels (<~0.3-0.4%) at all orientations that, however, remain non-negligible
until a few days after the merger and longer than previously found. Despite the
low levels, we find that the presence of a jet enhances the degree of
polarization at wavelengths ranging from 0.25 to 2.5\micron, an effect that is
found to increase with the jet luminosity. Thus, future photometric and
polarimetric campaigns should observe kilonovae in blue and red filters for a
few days after the merger to help constrain the properties of the ejecta (e.g.
composition) and jet.
