Neutrino-driven winds in binary neutron star mergers

Neutrinos are produced in copious amounts in the hot environment of a Binary Neutron Star Merger (BNSM). Although being the main source of cooling, neutrinos get scattered and absorbed while leaking out the post-merger system because of the large matter densities. If matter in the decoupling region gets enough momentum by neutrino absorption to overcome the gravitational well of the central merger remnant, neutrinos are able to power mass ejection called neutrino-driven winds. At the same time, neutrino absorption on nucleons affects the ejecta composition by changing the amount of neutrons. Since the neutron richness in the ejecta sets the strength of the r-process nucleosynthesis and the matter opacity, the macronova signal arising from the decay of the unstable r-process nuclei in the wind carries the signature of weak interactions in mergers as it shines in the optical wavelength band.
The detection of the blue macronova following the event GW170817 was a clear observational signature of weak interactions in BNSMs. However, other mass ejection channels beside neutrino-driven winds have been shown to potentially contribute to this optical counterpart of the macronova. In addition, relativistic jets launched from the central engine and drilling through the ejecta have been shown to impact the macronova signal, complicating our understanding of the diversity of macronova light curves. Looking forward to future, new macronova detections, it is therefore important to systematically study neutrino-driven wind contribution to macronova light curves for different total masses, mass ratios of the binary and Equation of States (EoSs), as well as accounting for jet-wind interplays for different jet properties.
For this purpose, I am going to talk about the implementation of an inexpensive, efficient approximation to the neutrino transport called Advanced Spectral Leakage (ASL). This scheme can be coupled to Lagrangian hydrodynamics with the Smoothed-Particle Hydrodynamics (SPH) approach to provide neutrino-driven wind profiles from dynamical simulations of BNSMs. In this way, it will be possible to systematically extract the associated macronova light curves and characterize their diversity.