TITLE: GCN CIRCULAR NUMBER: 22346 SUBJECT: GRB 180115A: Redshift from OSIRIS/GTC DATE: 18/01/15 22:57:40 GMT FROM: Antonio de Ugarte Postigo at IAA-CSIC A. de Ugarte Postigo (HETH/IAA-CSIC, DARK/NBI), Z. Cano, L. Izzo, C.C. Thoene, D.A. Kann (HETH/IAA-CSIC), N. Castro-Rodriguez (Grantecan, IAC, ULL), D. Perez Valladares (Grantecan) report on behalf of a larger collaboration: We observed the afterglow of GRB 180115A (Cannizzo et al. GCN 22335, Cano et al. GCN 22345) with OSIRIS at the 10.4m GTC telescope. The observation consisted of 3x900s exposure with grism R1000B, covering the range between 3700 and 7800 Angstrom and was performed under bad seeing conditions. The observation started at 20:32 UT (16.28 hr after the burst), and the acquisition image shows the afterglow at r=21.2+/-0.2. The spectrum shows a weak continuum over all the spectral range. The low signal to noise ratio of the spectrum only allows us to detect a single broad spectral feature that we identify as Lyman alpha at a redshift of 2.487.