GRBs as Probes of Massive Stars Near and Far

TL;DR

Long-duration gamma-ray bursts serve as powerful tools to study the death of massive stars across the universe, revealing diverse environments and helping understand their formation biases.

Contribution

This paper discusses efforts to build a complete GRB sample and analyze their environments, highlighting the diversity and potential biases in using GRBs as probes of massive stars.

Findings

GRB environments vary widely in metallicity and extinction.

Some GRB sightlines show significant Lyman continuum escape.

Detection of a 2175AA extinction bump in a GRB host.

Abstract

Long-duration gamma-ray bursts are the manifestations of massive stellar death. Due to the immense energy release they are detectable from most of the observable universe. In this way they allow us to study the deaths of single (or binary) massive stars possibly throughout the full timespan massive stars have existed in the Universe. GRBs provide a means to infer information about the environments and typical galaxies in which massive stars are formed. Two main obstacles remain to be crossed before the full potential of GRBs as probes of massive stars can be harvested: i) we need to build more complete and well understood samples in order not to be fooled by biases, and ii) we need to understand to which extent GRBs may be intrinsically biased in the sense that they are only formed by a limited subset of massive stars defined by most likely a restricted metallicity interval. We describe the status of an ongoing effort to build a more complete sample of long-duration GRBs with measured redshifts. Already now we can conclude that the environments of GRB progenitors are very diverse with metallicities ranging from solar to a hundredth solar and extinction ranging from none to A_V>5 mag. We have also identified a sightline with significant escape of Lyman continuum photons and another with a clear 2175AA extinction bump.