TITLE: GCN CIRCULAR NUMBER: 17672 SUBJECT: GRB 150403A: VLT/X-shooter redshift DATE: 15/04/04 12:06:05 GMT FROM: Dong Xu at DARK/NBI V. Pugliese (API/Uva), D. Xu (DARK/NBI), N. R. Tanvir, K. Wiersema (U. Leicester), J. P. U. Fynbo, B. Milvang-Jensen (DARK/NBI), V. D'Elia (ASI/ASDC and INAF/Roma) report on behalf of a larger collaboration: We observed the afterglow of GRB 150403A (Lien et al. GCN 17665; Longo et al. GCN 17667) with X-shooter at the Very Large Telescope (Paranal Observatory, Chile). Observations started at 08:44:48 UT on 2015-04-04 (i.e., 10.84 hr after the burst), and consisted of photometry in V-, r-, z-, and g- bands as well as spectroscopy of 4x600 s exposures covering the spectral range between 3000 and 25000 AA, equipped with UVB/VIS/NIR arms. The optical afterglow is well detected in each photometric image, and has m(R) ~ 19.1 mag at 10.85 hr post-burst, calibrated with nearby USNO B1 stars. For the spectroscopy, prominent absorption lines are detected in a continuum throughout the arms. In a preliminary reduction we detect absorption features of SII, SiIV, OI, SiII, SiII*, CII, CII*, CIV, AlII, NiII*, FeII, FeII*, MnI, MgII, MgI at a common redshift of z = 2.06, which is consistent with a broad Lya trough at the same redshift. We suggest this is the redshift of the GRB. We also detect an intervening system at z=1.76, identified with absorption lines of SiII, CIV, AlII, and so on. We acknowledge the excellent support provided by Paranal staff, and in particular Andrea Mehner, and Emanuela Pompei.