Neutron star binaries produced by binary-driven hypernovae, their mergers, and the link between long and short GRBs

TL;DR

This paper models binary-driven hypernovae (BdHNe) to explain long gamma-ray bursts, classifies them based on orbital periods, and simulates their evolution to predict neutron star mergers and short GRB characteristics.

Contribution

It provides a detailed classification of BdHNe, performs numerical simulations of BdHN II systems, and predicts properties of resulting neutron star mergers and short GRBs.

Findings

BdHN I produce GRBs >10^{52} erg with black hole formation.

BdHN II yield GRBs between 10^{50} and 10^{52} erg with stable neutron stars.

BdHN III result in lower energy GRBs <10^{50} erg and system disruption.

Abstract

The binary-driven hypernova (BdHN) model explains long gamma-ray bursts (GRBs) associated with supernovae (SNe) Ic through physical episodes that occur in a binary composed of a carbon-oxygen (CO) star and a neutron star (NS) companion in close orbit. The CO core collapse triggers the cataclysmic event, originating the SN and a newborn NS (hereafter $\nu$NS) at its center. The $\nu$NS and the NS accrete SN matter. BdHNe are classified based on the NS companion fate and the GRB energetics, mainly determined by the orbital period. In BdHNe I, the orbital period is of a few minutes, so the accretion causes the NS to collapse into a Kerr black hole (BH), explaining GRBs of energies $>10^{52}$ erg. BdHN II, with longer periods of tens of minutes, yields a more massive but stable NS, accounting for GRBs of $10^{50}$--$10^{52}$ erg. BdHNe III have still longer orbital periods (e.g., hours), so the NS companion has a negligible role, which explains GRBs with a lower energy release of $<10^{50}$ erg. BdHN I and II might remain bound after the SN, so they could form NS-BH and binary NS (BNS), respectively. In BdHN III, the SN likely disrupts the system. We perform numerical simulations of BdHN II to compute the characteristic parameters of the BNS left by them, their mergers, and the associated short GRBs. We obtain the mass of the central remnant, whether it is likely to be a massive NS or a BH, the conditions for disk formation and its mass, and the event's energy release. The role of the NS nuclear equation of state is outlined.