Angular Momentum Role in the Hypercritical Accretion of Binary-Driven Hypernovae

TL;DR

This paper investigates how angular momentum transfer during hypercritical accretion in binary-driven hypernovae influences neutron star collapse and jet formation, using full general relativity simulations to improve understanding of GRB progenitors.

Contribution

It provides the first estimates of angular momentum transfer in hypercritical accretion onto neutron stars within the IGC paradigm, highlighting the role of angular momentum excess in jet production.

Findings

Neutron star reaches mass-shedding or instability limit within seconds.

Maximum dimensionless angular momentum of neutron star is approximately 0.7.

Angular momentum transported exceeds neutron star's maximum support, leading to jet emission.

Abstract

The induced gravitational collapse (IGC) paradigm explains a class of energetic, $E_{\rm iso}\gtrsim 10^{52}$~erg, long-duration gamma-ray bursts (GRBs) associated with Ic supernovae, recently named binary-driven hypernovae (BdHNe). The progenitor is a tight binary system formed of a carbon-oxygen (CO) core and a neutron star companion. The supernova ejecta of the exploding CO core triggers a hypercritical accretion process onto the neutron star, which reaches in a few seconds the critical mass, and gravitationally collapses to a black hole emitting a GRB. In our previous simulations of this process we adopted a spherically symmetric approximation to compute the features of the hypercritical accretion process. We here present the first estimates of the angular momentum transported by the supernova ejecta, $L_{\rm acc}$, and perform numerical simulations of the angular momentum transfer to the neutron star during the hyperaccretion process in full general relativity. We show that the neutron star: i) reaches in a few seconds either mass-shedding limit or the secular axisymmetric instability depending on its initial mass; ii) reaches a maximum dimensionless angular momentum value, $[c J/(G M^2)]_{\rm max}\approx 0.7$; iii) can support less angular momentum than the one transported by supernova ejecta, $L_{\rm acc} > J_{\rm NS,max}$, hence there is an angular momentum excess which necessarily leads to jetted emission.