White Dwarf-Black Hole Binary Progenitors of Low Redshift Gamma-ray Bursts

TL;DR

This paper explores white dwarf-black hole mergers as potential progenitors of low-redshift long gamma-ray bursts, providing evidence and models to support their contribution to the observed deviations from star formation rates.

Contribution

It introduces the hypothesis that white dwarf-black hole mergers can explain a subset of low-redshift long GRBs, supported by analytic and numerical analysis.

Findings

White dwarf-black hole mergers can produce long GRBs with observed durations and energies.

The rate of these mergers aligns with the excess of low-redshift long GRBs.

Parameter space analysis shows these systems can account for a significant sub-population.

Abstract

Although there is strong evidence that many long GRBs are associated with the collapse of a massive star, tantalizing results in recent years have upended the direct association of all long GRBs with massive stars. In particular, kilonova signals in some long GRB light curves as well as a suggested uptick in the rate density of long GRBs at low redshifts (deviating significantly from the star formation rate) suggest that compact object mergers may be a non-negligible fraction of the long GRB population. Here we investigate the contribution of white dwarf-black hole mergers to the long GRB population. We present evidence for the deviation of the long GRB rate density from the star formation rate at low redshifts, and provide analytic and numerical arguments for why a white dwarf-black hole merger system may be a viable progenitor to explain this deviation. We show the range of parameter space in which the durations, energetics, and rates of these systems can account for a significant sub-population of low-redshift long GRBs.