r process nucleosynthesis from matter ejected in binary neutron star mergers
Abstract
When binary systems of neutron stars merge, a very small fraction of their rest mass is ejected, either dynamically or secularly. This material is neutronrich and its nucleosynthesis provides the astrophysical site for the production of heavy elements in the Universe, together with a kilonova signal confirming neutronstar mergers as the origin of short gammaray bursts. We perform full generalrelativistic simulations of binary neutronstar mergers employing three different nuclearphysics equations of state (EOSs), considering both equal and unequalmass configurations, and adopting a leakage scheme to account for neutrino radiative losses. Using a combination of techniques, we carry out an extensive and systematic study of the hydrodynamical, thermodynamical, and geometrical properties of the matter ejected dynamically, employing the WinNet nuclearreaction network to recover the relative abundances of heavy elements produced by each configurations. Among the results obtained, three are particularly important. First, we find that, within the sample considered here, both the properties of the dynamical ejecta and the nucleosynthesis yields are robust against variations of the EOS and masses. Second, using a conservative but robust criterion for unbound matter, we find that the amount of ejected mass is ≲10^{3} M_{⊙}, hence at least one order of magnitude smaller than what normally assumed in modelling kilonova signals. Finally, using a simplified and grayopacity model we assess the observability of the infrared kilonova emission finding, that for all binaries the luminosity peaks around ∼1 /2 day in the H band, reaching a maximum magnitude of 13 , and decreasing rapidly after one day.
 Publication:

Physical Review D
 Pub Date:
 December 2017
 DOI:
 10.1103/PhysRevD.96.124005
 arXiv:
 arXiv:1709.09630
 Bibcode:
 2017PhRvD..96l4005B
 Keywords:

 General Relativity and Quantum Cosmology;
 Astrophysics  High Energy Astrophysical Phenomena
 EPrint:
 24 pages, 18 figures, submitted to PRD