A Common Envelope Binary Star Origin of Long Gamma-ray Bursts

TL;DR

This paper proposes a binary star merger model involving white dwarfs and helium star cores as the origin of long gamma-ray bursts, explaining their rarity, association with supernovae, and occurrence near star-forming regions.

Contribution

It introduces a novel binary evolution scenario for long gamma-ray bursts, linking their occurrence to common envelope mergers of specific stellar remnants.

Findings

Population synthesis supports the proposed rate of gamma-ray bursts.

The model predicts a correlation between burst rate and star formation rate.

Progenitors are of intermediate mass, differing from typical high-mass star models.

Abstract

The stellar origin of gamma-ray bursts can be explained by the rapid release of energy in a highly collimated, extremely relativistic jet. This in turn appears to require a rapidly spinning highly magnetised stellar core that collapses into a magnetic neutron star or a black hole within a relatively massive envelope. They appear to be associated with type Ib/c supernovae but, with a birthrate of around 10^{-6}-10^{-5} per year per galaxy, they are considerably rarer than such supernovae in general. To satisfy all these requirements we hypothesize a binary star model that ends with the merging of an oxygen neon white dwarf with the carbon-oxygen core of a naked helium star during a common envelope phase of evolution. The rapid spin and high magnetic field are natural consequences of such a merging. The evolution that leads to these progenitors is convoluted and so naturally occurs only very rarely. To test the hypothesis we evolve a population of progenitors and find that the rate is as required. At low metallicity we calculate that a similar fraction of stars evolve to this point and so would expect the gamma-ray burst rate to correlate with the star formation rate in any galaxy. This too is consistent with observations. These progenitors, being of intermediate mass, differ radically from the usually postulated high-mass stars. Thus we can reconcile observations that the bursts occur close to but not within massive star associations.