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

Context. Long gamma-ray bursts (LGRBs) are generally observed in low-metallicity environments. However, 10% to 20% of LGRBs at redshift z < 2 are associated with near-solar to super-solar metallicity environments, remaining unexplained by traditional LGRB formation pathways that favor 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 used <ns0:monospace>POSYDON</ns0:monospace>, 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 investigated 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.