TITLE: GCN CIRCULAR NUMBER: 18213 SUBJECT: GRB 150818A: Spectroscopic confirmation of the SN from GTC DATE: 15/08/31 17:49:21 GMT FROM: Antonio de Ugarte Postigo at IAA-CSIC A. de Ugarte Postigo (IAA-CSIC, DARK/NBI), Z. Cano (U. Iceland), D. A. Perley (DARK/NBI), S. Schulze (PUC, MAS), D. Xu (NAOC/CAS), R. Sanchez-Ramirez (IAA-CSIC), D. Malesani (DARK/NBI), G. Lombardi (GRANTECAN, IAC, ULL), and A. Garcia (GRANTECAN), R. Scarpa (GRANTECAN) report on behalf of a larger collaboration: We observed the counterpart of GRB 150818A (D'Elia et al. GCN 18152; Marshall et al. GCN 18155; McCauley et al. GCN 18161; Mazaeva et al. GCN 18175; Sanchez-Ramirez et al. GCN 18177; Mazaeva et al. GCN 18182, GCN 18189, GCN 18205; Schulze et al. GCN 18179) with the 10.4 m GTC telescope (+OSIRIS) on the 29th August 2015 (11.4 days after the burst). The observation consisted of 3x900 s spectroscopy using the R1000B grism (3700-7800 AA coverage with a resolution of ~1000) plus g-, r- and i-band imaging. We detect a point-like source at the location of the afterglow superposed on top of an extended source. The combined spectrum shows broad features typical of a broad-lined Type Ic SN near maximum light, thus confirming the detection of a rising supernova proposed by Mazaeva et al. (GCN 18205). The spectrum also shows narrow emission features of [OII], [OIII] and H-beta at z=0.282 (Sanchez-Ramirez et al. GCN 18177).