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


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Letter to the Editor

VLT identification of the optical afterglow of the gamma-ray burst GRB 000131 at [FORMULA] *

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 14

1 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[FORMULA] absorption edge at 6700 Å. This places GRB 000131 at a redshift of [FORMULA]. The inferred isotropic energy release in gamma rays alone was [FORMULA] (depending on the assumed cosmology). The rapid power-law decay of the afterglow (index [FORMULA]=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 [FORMULA] 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

© European Southern Observatory (ESO) 2000

Online publication: December 15, 2000

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