High-Resolution Spectroscopy of GRB030226: Features of a Massive Star Progenitor or Intervening Absorption Systems?

TL;DR

This study analyzes high-resolution spectra of GRB030226 revealing multiple absorption systems, concluding that some are intervening galaxies rather than circumstellar wind features, challenging previous assumptions about the progenitor environment.

Contribution

It provides the first detailed high-resolution spectral analysis of GRB host and intervening systems, clarifying their origins and challenging prior circumstellar wind interpretations.

Findings

High column densities of low-ionization species suggest intervening systems.

Two absorption systems are similar to Damped Lyman-alpha systems in QSO sight lines.

The z=1.96337 system is likely an intervening galaxy, not circumstellar material.

Abstract

We present a high-resolution Keck/ESI spectrum of GRB, which exhibits four absorption systems at z=1.04329, 1.95260, 1.96337, and 1.98691. The two highest redshift systems, separated by about 2400 km/s, have been previously suspected as kinematic features arising in the circumstellar wind around the progenitor star. However, the high column densities of low-ionization species (including possibly neutral hydrogen) in the blue-shifted system, are inconsistent with the expected highly ionized state of the circumstellar wind from the massive progenitor star, even prior to the GRB explosion. This conclusion is also supported by the lack of detectable absorption from fine-structure transitions of SiII and FeII. Instead we conclude that the two redshift systems are similar to multiple DLAs found in QSO sight lines with a similar velocity separation and chemical abundance of [Cr/Fe] and [Zn/Fe]. The absorption system at z=1.96337 is likely an intervening low-mass galaxy, possibly related to the GRB host as part of a forming large-scale structure.