The r-process in proto-neutron star winds with anisotropic neutrino emission

The astrophysical origin of the r-process nuclei is still unknown. Even the most promising scenario, the neutrinodriven winds from a nascent neutron star, encounters severe difficulties in obtaining the requisite entropy and short dynamic timescale for the r-process. In this study, the effect of anisotropy in neutrino emission from a proto-neutron star surface is examined with semianalytic neutrino-driven wind models. The increase of neutrino number density in the wind owing to the anisotropy is modeled schematically by enhancing the effective neutrino luminosity. It is shown that the neutrino heating rate from neutrino-antineutrino pair annihilation into electronpositron pairs can significantly increase owing to the anisotropy and can play a dominant role in the heating of wind material. A factor of 5 increase in the effective neutrino luminosity results in a 50% higher entropy and a factor of 10 shorter dynamic timescale owing to this enhanced neutrino heating. The nucleosynthesis calculations show that this change is enough for the robust r-process, producing the third abundance peak (A=195) and beyond. Future multidimensional studies with accurate neutrino transport will be needed if such anisotropy relevant to the current scenario (more than a factor of a few) is realized during the wind phase (similar to 1 - 10 s).