The host of GRB 060206: kinematics of a distant galaxy

TL;DR

This study analyzes the kinematics and environment of the distant galaxy hosting GRB 060206 through early optical spectroscopy, revealing multiple absorption systems, fine-structure lines, and the host galaxy's properties.

Contribution

First detailed spectroscopic analysis of GRB 060206's host galaxy and intervening system, including velocity structures and UV pumping mechanisms of fine-structure lines.

Findings

Detected four velocity systems indicating starburst wind shells.

Identified UV pumping as the origin of fine-structure lines.

Constrained the host galaxy's brightness and the intervening system's properties.

Abstract

We present early (starting 1.6h after the burst) WHT/ISIS optical spectroscopy of the afterglow of the gamma-ray burst GRB 060206 detecting a range of metal absorption lines and their fine-structure transitions. Additional information is provided by the afterglow lightcurve. The resolution and wavelength range of the spectra and the bright afterglow facilitate a detailed study and fitting of the absorption line systems in order to derive column densities. We also use deep imaging to detect the host galaxy and probe the nature of an intervening system at z = 1.48 seen in absorption in the afterglow spectra. We detect four discrete velocity systems in the resonant metal absorption lines, best explained by shells within and/or around the host created by starburst winds. The fine-structure lines have no less than three components with strengths decreasing from the redmost components. We therefore suggest that the fine-structure lines are best explained to be produced by UV pumping from which follows that the redmost component is the one closest to the burst where also NV was detected. The host is detected in deep HST imaging with F814W_AB = 27.48 +- 0.19 mag and a 3 sigma upper limit of H = 20.6 mag (Vega) is achieved. A candidate counterpart for the intervening absorption system is detected as well, which is quite exceptional for an absorber in the sightline towards a GRB afterglow. The intervening system shows no temporal evolution as claimed by Hao et al. (2007) which we prove from our WHT spectra taken before and Subaru spectra taken during the observations from Hao et al.