VLT identification of the optical afterglow of the gamma-ray burst GRB000131 at z=4.50

M.I. Andersen, J. Hjorth, B.L. Jesen, L.K. Hunt, J. Gorosabel, P. Møller, J. Fynbo, R.M. Kippen, B. Thomsen, F.L. Olsen, L. Christensen, M. Vestergaard, N. Masetti, E. Palazzi, K. Hurley, T. Cline, L. Kaper, A.O. Jaunsen

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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 alpha absorption edge at 6700 Angstrom. This places GRB 000131 at a redshift of 4.500 +/- 0.015. The inferred isotropic energy release in gamma rays alone was similar to 10(54) erg (depending on the assumed cosmology). The rapid power-law decay of the afterglow (index alpha = 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.
Original languageEnglish
JournalAstronomy & Astrophysics
Issue number1
Pages (from-to)L54-L61
Publication statusPublished - 2000


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