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

Alberto Javier Castro-Tirado, Palle Moller, Guillermo Miguel Garcia-Segura, Javier Gorosabel, Enrique Perez, Antonio de Ugarte Postigo, Enrique Solano, David Barrado, Sylvio Klose, David Alexander Kann, Jose Maria Castro Ceron, Chryssa Kouveliotou, Johan Peter Uldall Fynbo, Jens Hjorth, Holger Pedersen, Elena Pian, Evert Rol, Eliana Palazzi, Nicola Masetti, Nial R TanvirPaul Marijn Vreeswijk, Michael Ingemann Andersen, Andrew S Fruchter, Jochen Greiner, Ralph A M J Wijers, Edward P J van den Heuvel

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Aims. We analyse the distribution of matter around the progenitor star of gamma-ray burst GRB 021004 and the properties of its host galaxy with high-resolution echelle and near-infrared spectroscopy. Methods. Observations were taken by the 8.2 m Very Large Telescope with the Ultraviolet and Visual Echelle spectrograph (UVES) and the Infrared Spectrometer And Array Camera (ISAAC) between 10 and 14 h after the onset of the event. Results. We report the first detection of emission lines from a GRB host galaxy in the near-infrared, detecting Ha and the [O III] doublet. These allow us to independently measure the systemic redshift (z = 2.3304 +/- 0.0005), which is not contaminated by absorption as the Lya line is, and infer the host galaxy properties. From the visual echelle spectroscopy, we find several absorption-line groups spanning a range of about 3000 km s-1 in velocity relative to the redshift of the host galaxy. The absorption profiles are very complex with both velocity-broadened components extending over several 100 km s-1 and narrow lines with velocity widths of only 20 km s-1. By analogy with QSO absorption line studies, the relative velocities, widths, and degrees of ionization of the lines ( line- locking , ionization-velocity correlation ) show that the progenitor had both an extremely strong radiation field and several distinct mass-loss phases (winds). Conclusions. These results are consistent with GRB progenitors being massive stars, such as luminous blue variables (LBVs) or Wolf-Rayet stars, providing a detailed picture of the spatial and velocity structure of the GRB progenitor star at the time of explosion. The host galaxy is a prolific star-forming galaxy with a SFR of 40 M.
Original languageEnglish
Pages (from-to)1 - 9
Number of pages9
JournalAstronomy & Astrophysics
Issue number9
Publication statusPublished - 2010
Externally publishedYes

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