The interstellar medium in the environment of the supernova-less long-duration GRB 111005A

TL;DR

This study investigates the interstellar medium of the host galaxy of GRB 111005A, a long-duration gamma-ray burst without an associated supernova, revealing unique ISM properties that suggest a different progenitor scenario.

Contribution

It provides detailed ISM characterization of the host galaxy of a supernova-less long GRB, highlighting differences from typical GRB hosts and proposing alternative progenitor explanations.

Findings

ISM is smooth with no recent gas inflow or outflow.

The host galaxy shows irregularities possibly due to interactions or mergers.

The environment suggests a non-massive star progenitor for GRB 111005A.

Abstract

Long ($>2$ s) gamma ray bursts (GRBs) are associated with explosions of massive stars, although in three instances, supernovae (SNe) have not been detected, despite deep observations. With new HI line and archival optical integral field spectroscopy data, we characterize the interstellar medium (ISM) of the host galaxy of one of these events, GRB 111005A, in order to shed light on the unclear nature of these peculiar objects. We found that the atomic gas, radio continuum, and rotational patterns are in general very smooth throughout the galaxy, which does not indicate a recent gas inflow or outflow. There is also no gas concentration around the GRB position. The ISM in this galaxy differs from that in hosts of other GRBs and SNe, which may suggest that the progenitor of GRB 111005A was not an explosion of a very massive star (e.g. a compact object merger). However, there are subtle irregularities of the GRB 111005A host (most at a $2\sigma$ level), which may point to a weak gas inflow or interaction. Since in the SE part of the host there is 15% more atomic gas and twice less molecular gas than in NW part, the molecular gas fraction is low. In the SE part there is also a region with very high H$\alpha$ equivalent width. There is more continuum 1.4 GHz emission to the SE and an S-shaped warp in the UV. Finally, there is also a low-metallicity region 3.5" (1 kpc) from the GRB position. Two galaxies within 300 kpc or a past merger can be responsible for these irregularities.