GRB 021004: Tomography of a gamma-ray burst progenitor and its host galaxy*
Instituto de Astrofísica de Andalucía (IAA-CSIC), Glorieta de la Astronomía s/n, 18.008 Granada, Spain e-mail: email@example.com
2 European Southern Observatory, Karl-Schwarzschild-Strasse 2, 85748 Garching bei München, Germany
3 Instituto de Astronomía, Universidad Nacional Autónoma de México, Apdo. Postal 877, Ensenada 22800, Baja California, México
4 INAF, Osservatorio Astronomico di Brera, via E. Bianchi 46, 23807 Merate (LC), Italy
5 Laboratorio de Astrofísica Estelar y Exoplanetas, Dpto. Astrofísica, Centro de Astrobiología (CSIC/INTA), PO Box 78, 28691 Villanueva de la Cañada, Madrid, Spain
6 Calar Alto Observatory, Centro Astronómico Hispano Alemán, C . Jesús Durbán Remón, 2-2, 04004 Almería, Spain
7 Thüringer Landessternwarte Tautenburg, Sternwarte 5, 07778 Tautenburg, Germany
8 European Space Agency (ESA), European Space Astronomy Centre (ESAC), PO Box, Apdo. de correos 78, 28691 Villanueva de la Cañada, Madrid, Spain
9 NASA Marshall Space Flight Center, NSSTC, 320 Sparkman Drive, Huntsville, Alabama 35805, USA
10 Dark Cosmology Centre, Niels Bohr Institute, University of Copenhagen, Juliane Maries Vej 30, 2100 København Ø, Denmark
11 INAF - Osservatorio Astronomico di Trieste, via Tiepolo, 11, 34131 Trieste, Italy
12 Scuola Normale Superiore di Pisa, Piazza dei Cavalieri 7, 56126 Pisa, Italy
13 Department of Physics & Astronomy, University of Leicester, University Road, Leicester LE1 7RH, UK
14 Astronomical Institute “Anton Pannekoek”, University of Amsterdam, PO number 94249, 1090 GE, Amsterdam, The Netherlands
15 INAF - IASF di Bologna, via Gobetti 101, 40129 Bologna, Italy
16 Space Telescope Science Institute, 3700 San Martín Dr, Baltimore, MD 21218-2463, USA
17 Max-Planck-Institut für extraterrestrische Physik, 85748 Garching, Germany
Accepted: 26 March 2010
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 Hα 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 Lyα 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 yr-1.
Key words: gamma-ray bust: general / techniques: spectroscopic / stars: Wolf-Rayet / galaxies: starburst / cosmology: observations
© ESO, 2010