Astron. Astrophys. 364, L54-L61 (2000)

Letter to the Editor

VLT identification of the optical afterglow of the gamma-ray burst GRB 000131 at  ^*

M.I. Andersen ¹, J. Hjorth ², H. Pedersen ², B.L. Jensen ², L.K. Hunt ³, J. Gorosabel ⁴, P. Moller ⁵, J. Fynbo ^2,5, R.M. Kippen ⁶, B. Thomsen ⁷, L.F. Olsen ², L. Christensen ², M. Vestergaard ⁸, N. Masetti ⁹, E. Palazzi ⁹, K. Hurley ¹⁰, T. Cline ¹¹, L. Kaper ¹³ and A.O. Jaunsen <sup>14

1</sup> University of Oulu, Division of Astronomy, P.O. Box 3000, 90014 Oulu, Finland (Michael.Andersen@oulu.fi)
² University of Copenhagen, Astronomical Observatory, Juliane Maries Vej 30, 2100 Copenhagen O, Denmark
³ Centro per l'Astronomia Infrarossa e lo Studio del Mezzo Interstellare, CNR, Largo E. Fermi 5, 50125 Firenze, Italy
⁴ Danish Space Research Institute, Juliane Maries Vej 30, 2100 Copenhagen O, Denmark
⁵ European Southern Observatory, Karl-Schwarzschild-Strasse 2, 85748 Garching, Germany
⁶ University of Alabama in Huntsville and NASA/Marshall Space Flight Center, SD50, Huntsville, AL 35812, USA
⁷ University of Aarhus, Institute of Physics and Astronomy, 8000 Århus C, Denmark
⁸ Ohio State University, Astronomy Department, 140 West 18th Avenue, Columbus, OH 43210-1173, USA
⁹ Instituto Tecnologie e Studio Radiazoni Extraterresti, CNR, Via Gobetti 101, 40129 Bologna, Italy
¹⁰ University of California, Space Science Laboratory, Berkeley, CA 94720-7450, USA
¹¹ NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA
¹² Sterrenkundig Instituut "Anton Pannekoek", Kruislaan 403, 1098 SJ Amsterdam, The Netherlands
¹³ University of Oslo, Institute of Theoretical Astrophysics, PB 1029, Blindern, 0315 Oslo, Norway

Received 18 August 2000 / Accepted 6 October 2000

Abstract

We report the discovery of the gamma-ray burst GRB 000131 and its optical afterglow. The optical identification was made with the VLT 84 hours after the burst following a BATSE detection and an Inter Planetary Network localization. GRB 000131 was a bright, long-duration GRB, with an apparent precursor signal 62 s prior to trigger. The afterglow was detected in ESO VLT, NTT, and DK1.54m follow-up observations. Broad-band and spectroscopic observations of the spectral energy distribution reveals a sharp break at optical wavelengths which is interpreted as a Ly absorption edge at 6700 Å. This places GRB 000131 at a redshift of . The inferred isotropic energy release in gamma rays alone was (depending on the assumed cosmology). The rapid power-law decay of the afterglow (index =2.25, similar to bursts with a prior break in the lightcurve), however, indicates collimated outflow, which relaxes the energy requirements by a factor of 200. The afterglow of GRB 000131 is the first to be identified with an 8-m class telescope.

Key words: cosmology: observations gamma rays: bursts ISM: dust, extinction

* Based on observations collected at the European Southern Observatory, La Silla and Paranal, Chile (ESO Programmes 64.H-0573, 64.H-0580, 64.O-0187, and 64.H-0313)

Send offprint requests to: M.I. Andersen

Correspondence to: Michael.Andersen@oulu.fi

SIMBAD Objects

Contents

• 1. Introduction
• 2. Detection of the gamma-ray burst
• 3. Localization and identification of the afterglow
• 4. Follow-up observations and data analysis
  • 4.1. Image analysis and photometry
  • 4.2. Optical images
  • 4.3. Near-infrared images
  • 4.4. Spectroscopy
• 5. Discussion
  • 5.1. The light curve of the afterglow
  • 5.2. Spectral energy distribution
  • 5.3. The spectroscopic redshift of GRB 000131
• 6. Conclusions
• Acknowledgements
• References

© European Southern Observatory (ESO) 2000

Online publication: December 15, 2000
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