A new long gamma-ray burst formation pathway at solar metallicity

TL;DR

This paper proposes a new binary evolution pathway for long gamma-ray burst formation at solar metallicity, explaining observed LGRBs in high-metallicity environments through stable reverse mass transfer in binary stars.

Contribution

It introduces a novel LGRB formation channel at high metallicity via binary interactions, supported by population synthesis modeling and energy calculations.

Findings

Stable reverse mass transfer produces rapidly rotating, stripped stars at collapse.

This channel accounts for 10-20% of the local LGRB rate density.

The predicted rate varies between 1 and 100 Gpc$^{-3}$ yr$^{-1}$ depending on assumptions.

Abstract

Context. Long gamma-ray bursts (LGRBs) are generally observed in low-metallicity environments. However, 10 to 20 per cent of LGRBs at redshift $z<2$ are associated with near-solar to super-solar metallicity environments, remaining unexplained by traditional LGRB formation pathways that favour low metallicity progenitors. Aims. In this work, we propose a novel formation channel for LGRBs that is dominant at high metallicities. We explore how a stripped primary star in a binary can be spun up by a second, stable reverse-mass-transfer phase, initiated by the companion star. Methods. We use POSYDON, a state-of-the-art population synthesis code that incorporates detailed single- and binary-star mode grids, to investigate the metallicity dependence of the stable reverse-mass-transfer LGRB formation channel. We determine the available energy to power an LGRB from the rotational profile and internal structure of a collapsing star, and investigate how the predicted rate density of the proposed channel changes with different star formation histories and criteria for defining a successful LGRB. Results. Stable reverse mass transfer can produce rapidly rotating, stripped stars at collapse. These stars retain enough angular momentum to account for approximately 10-20% of the observed local LGRB rate density, under a reasonable assumption for the definition of a successful LGRB. However, the local rate density of LGRBs from stable reverse mass transfer can vary significantly, between 1 and 100 Gpc$^{-3}$ yr$^{-1}$, due to strong dependencies on cosmic star formation rate and metallicity evolution, as well as the assumed criteria for successful LGRBs.