Black hole-neutron star binaries with high spins and large mass asymmetries: III. Properties of the ejected material and its electromagnetic signatures

Compact binary systems consisting of a black hole (BH) and a neutron star (NS) are expected to provide detectable signals both in the gravitational wave and in the electromagnetic channels, thus representing excellent sources for multi-messenger astronomy. In this third paper in a series, we report on the geometric and thermodynamic properties of the purely dynamical ejecta component modeled in our general-relativistic magnetohydrodynamical simulations of BHNS systems over a comprehensive binary parameter space consisting of large mass ratio and high BH spin. The tidal disruption and dynamical mass ejection is studied by monitoring the transfer of energy and angular momentum to matter for the particular case of a highly unequal-mass binary with large BH spin, extending known results for low-mass-ratio, irrotational BHNS binaries. By varying the binary parameters, we investigate their influence on the geometric, thermodynamic, and kinematic properties of the ejected matter. Furthermore, we employ the nuclear-reaction network SkyNet to obtain the elemental abundances resulting from the r-process active in the ejecta and study how they depend on the properties of the progenitor objects. Finally, using the radiative-transfer code POSSIS, we compute the kilonova light-curves from the results of our simulations, discuss their bolometric and optical/near-infrared evolution, and compare them with the AT2017gfo data and upper-limits for S190814bv, finding overall consistency.