VLT identification of the optical afterglow of the gamma-ray burst GRB 000131 at z=4.50

We report the discovery of the gamma-ray burst GRB 000131 and its optical a fterglow. The optical identification was made with the VLT 84 hours after t he burst following a BATSE detection and an Inter Planetary Network localiz ation. GRB 000131 was a bright, long-duration GRB, with an apparent precurs or signal 62 s prior to trigger. The afterglow was detected in ESO VLT, NTT , and DK1.54m follow-up observations. Broad-band and spectroscopic observat ions of the spectral energy distribution reveals a sharp break at optical w avelengths which is interpreted as a Ly alpha absorption edge at 6700 Angst rom. 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 (dep ending on the assumed cosmology). The rapid power-law decay of the afterglo w (index alpha = 2.25, similar to bursts with a prior break in the lightcur ve), however, indicates collimated outflow which relaxes the energy require ments by a factor of < 200. The afterglow of GRB 000131 is the first to be identified with an 8-m class telescope.