TITLE: GCN GRB OBSERVATION REPORT NUMBER: 3176 SUBJECT: GRB 050401: VLT spectroscopic redshift DATE: 05/04/03 19:59:02 GMT FROM: Jens Hjorth at U.Copenhagen Johan P. U. Fynbo, Brian L. Jensen, Jens Hjorth (Niels Bohr Institute), Klaas Wiersema, Rhaana Starling (U. Amsterdam), Paul Vreeswijk (ESO), Evert Rol, Andrew Levan (U. Leicester), Sara Ellison (U. Victoria), Nicola Masetti (IASF-Bologna) report on behalf of a larger collaboration: "Using FORS2 on the Very Large Telescope we have obtained spectra of the afterglow of GRB 050401 (GCN 3161, 3162, 3163) on 2005, April 2. We detect several absorption lines consistent with two absorption systems at redshifts z = 2.50 and z = 2.90. The likely redshift of GRB 050401 is hence z = 2.90. For a standard cosmology (H_0 = 70 km/s/Mpc, Omega_m = 0.3, Omega_w = 0.7, w = -1) the Swift fluence (GCN 3173) corresponds to an isotropic energy release of 2.6 x 10^53 erg. We thank Paul Price for providing a finding chart for the optical afterglow and the ESO staff for excellent support."