Neutrino-driven winds in the aftermath of a neutron star merger: nucleosynthesis and electromagnetic transients

TL;DR

This paper investigates neutrino-driven winds after neutron star mergers, analyzing nucleosynthesis yields, their dependence on remnant lifetime, and resulting electromagnetic transients, including light curves and spectral features.

Contribution

It provides a detailed nucleosynthesis analysis of neutrino-driven winds in neutron star mergers, highlighting the impact of remnant lifetime and ejecta angles on element production and electromagnetic signals.

Findings

Yields depend on neutron star lifetime and polar angle.

Up to 9e-3 solar masses become unbound within 200 ms.

Light curve peaks in blue band after 4 hours, infrared peak after 3-4 days.

Abstract

We present a comprehensive nucleosynthesis study of the neutrino-driven wind in the aftermath of a binary neutron star merger. Our focus is the initial remnant phase when a massive central neutron star is present. Using tracers from a recent hydrodynamical simulation, we determine total masses and integrated abundances to characterize the composition of unbound matter. We find that the nucleosynthetic yields depend sensitively on both the life time of the massive neutron star and the polar angle. Matter in excess of up to $9 \cdot 10^{-3} M_\odot$ becomes unbound until $\sim 200~{\rm ms}$. Due to electron fractions of $Y_{\rm e} \approx 0.2 - 0.4$ mainly nuclei with mass numbers $A < 130$ are synthesized, complementing the yields from the earlier dynamic ejecta. Mixing scenarios with these two types of ejecta can explain the abundance pattern in r-process enriched metal-poor stars. Additionally, we calculate heating rates for the decay of the freshly produced radioactive isotopes. The resulting light curve peaks in the blue band after about $4~{\rm h}$. Furthermore, high opacities due to heavy r-process nuclei in the dynamic ejecta lead to a second peak in the infrared after $3-4~{\rm d}$.