The Population of Helium-Merger Progenitors: Observational Predictions

TL;DR

This paper predicts observational features of helium-merger gamma-ray burst progenitors by combining population synthesis models with current understanding of GRB engines and common envelope evolution.

Contribution

It introduces a novel approach coupling population synthesis with GRB models to predict observable signatures of helium-merger progenitors.

Findings

Distinct environmental signatures around helium-merger GRBs.

Some mergers do not produce GRBs, expanding the understanding of astrophysical transients.

Predictions enable identification of past mergers in GRB afterglows.

Abstract

The helium-merger gamma-ray burst progenitor is produced by the rapid accretion onto a compact remnant (neutron star or black hole) when it undergoes a common envelope inspiral with its companion's helium core. This merger phase produces a very distinct environment around these outbursts and recent observations suggest that, in some cases, we are detecting the signatures of the past merger in the GRB afterglow. These observations allow us, for the first time, to study the specific features of the helium merger progenitor. In this paper, we couple population synthesis calculations to our current understanding of gamma-ray burst engines and common envelope evolution to make observational predictions for the helium-merger gamma-ray burst population. Many mergers do not produce GRB outbursts and we discuss the implications of these mergers with the broader population of astrophysical transients.