Production of Nickel-56 in black hole-neutron star merger accretion disk outflows

The likely outcome of a compact object merger event is a central black hole surrounded by a rapidly accreting torus of debris. This disk of debris is a rich source of element synthesis, the outcome of which is needed to predict electromagnetic counterparts of individual events and to understand the contribution of mergers to galactic chemical evolution. Here we study disk outflow nucleosynthesis in the context of a two-dimensional, time-dependent black hole-neutron star merger accretion disk model. We use two time snapshots from this model to examine the impact of the evolution of the neutrino fluxes from the disk on the element synthesis. While the neutrino fluxes from the early-time disk snapshot appear to favor neutron-rich outflows, by the late-time snapshot the situation is reversed. As a result we find copious production of Nickel-56 in the outflows.