Energy-dependent and energy-integrated two-moment general-relativistic neutrino transport simulations of hypermassive neutron star

TL;DR

This study compares energy-dependent and energy-integrated neutrino transport methods in general-relativistic simulations of hypermassive neutron stars, revealing significant differences in disk, ejecta, and neutrino signals.

Contribution

It demonstrates that energy-dependent neutrino transport provides more accurate modeling of neutron star merger remnants compared to energy-integrated schemes.

Findings

Energy-dependent transport yields more neutron-rich, thicker disks.

Ejecta are more massive and neutron-rich with energy-dependent schemes.

Neutrino energies and luminosities are about 30% higher in energy-dependent simulations.

Abstract

We compare two-moment based \emph{energy-dependent} and 3 variants of \emph{energy-integrated} neutrino transport general-relativistic magnetohydrodynamics simulations of hypermassive neutron star. To study the impacts due to the choice of the neutrino transport schemes, we perform simulations with the same setups and input neutrino microphysics. We show that the main differences between energy-dependent and energy-integrated neutrino transport are found in the disk and ejecta properties, as well as in the neutrino signals. The properties of the disk surrounding the neutron star and the ejecta in energy-dependent transport are very different from the ones obtained using energy-integrated schemes. Specifically, in the energy-dependent case, the disk is more neutron-rich at early times, and becomes geometrically thicker at later times. In addition, the ejecta is more massive, and on average more neutron-rich in the energy-dependent simulations. Moreover, the average neutrino energies and luminosities are about 30\% higher. Energy-dependent neutrino transport is necessary if one wants to better model the neutrino signals and matter outflows from neutron star merger remnants via numerical simulations.