A quiescent galaxy at the position of the long GRB 050219A

TL;DR

This paper reports the discovery of a long gamma-ray burst host galaxy that is an old, quiescent early-type galaxy, challenging the typical association of such bursts with star-forming galaxies and expanding understanding of their environments.

Contribution

It presents the first case of a long GRB occurring in an early-type, post-starburst galaxy, showing that GRBs can originate in diverse galaxy types.

Findings

Host galaxy is an old, quiescent early-type galaxy at z=0.211

The galaxy has an extremely low specific star-formation rate

This is the first long GRB host identified as an early-type galaxy

Abstract

Long-duration gamma-ray bursts (LGRBs) are produced by the collapse of very massive stars. Due to the short lifetime of their progenitors, LGRBs pinpoint star-forming galaxies. We present here a multi-band search for the host galaxy of the long dark GRB 050219A within the enhanced Swift/XRT error circle. We used spectroscopic observations acquired with VLT/X-shooter to determine the redshift and star-formation rate of the putative host galaxy. We compared the results with the optical/IR spectral energy distribution obtained with different facilities. Surprisingly, the host galaxy is a old and quiescent early-type galaxy at z = 0.211 characterised by an unprecedentedly low specific star-formation rate. It is the first LGRB host to be also an early-type post-starburst galaxy. This is further evidence that GRBs can explode in all kind of galaxies, with the only requirement being an episode of star-formation.