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We analyse the distribution of matter around the progenitor star of gamma-rayburst GRB 021004 as well as the properties of its host galaxy withhigh-resolution echelle as well as near-infrared spectroscopy. Observationswere taken by the 8.2m Very Large Telescope with the Ultraviolet and VisualEchelle spectrograph (UVES) and the Infrared Spectrometer And Array Camera(ISAAC) between 10 and 14 hours after the onset of the event. We report thefirst detection of emission lines from a GRB host galaxy in the near-infrared,detecting H-alpha and the [O III] doublet. These allow an independentmeasurement of the systemic redshift (z = 2.3304 +/- 0.0005) which is notcontaminated by absorption as the Ly-alpha line is, and the deduction ofproperties of the host galaxy. From the visual echelle spectroscopy, we findseveral absorption line groups spanning a range of about 3,000 km/s in velocityrelative to the redshift of the host galaxy. The absorption profiles are verycomplex with both velocity-broadened components extending over several 100 km/sand narrow lines with velocity widths of only 20 km/s. By analogy with QSOabsorption line studies, the relative velocities,widths, and degrees ofionization of the lines ("line-locking", "ionization--velocity correlation")show that the progenitor had both an extremely strong radiation field andseveral distinct mass loss phases (winds). These results are consistent withGRB progenitors being massive stars, such as Luminous Blue Variables (LBVs) orWolf--Rayet stars, providing a detailed picture of the spatial and velocitystructure of the GRB progenitor star at the time of explosion. The host galaxyis a prolific star-forming galaxy with a SFR of about 40 solar masses per year.

GRB 021004: Tomography of a gamma-ray burst progenitor and its host galaxy