TITLE: GCN CIRCULAR NUMBER: 11993 SUBJECT: GRB 110503A: Redshift from 10.4m GTC DATE: 11/05/03 22:50:27 GMT FROM: Antonio Deugarte at IAA-CSIC A. de Ugarte Postigo (DARK/NBI), A.J. Castro-Tirado, J.C. Tello (IAA-CSIC), A. Cabrera Lavers, D. Reverte (GTC) report on behalf of a larger collaboration: We have observed the afterglow of GRB 110503A (Stamatikos et al. GCNC11991) using OSIRIS at the 10.4m GTC telescope (La Palma, Spain). Observations consisted on 2x900s using the R500B grating, starting at 21:36UT (4.0h after the burst). In a preliminary analysis, using archival calibrations, we detect a high signal to noise ratio continuum with absorption features that include SiIV, SiII, CIV, FeII, AlII, AlIII, ZnII, MgII and MgI at a common redshift of z=1.613, which we identify as the redshift of the afterglow.