TITLE: GCN CIRCULAR NUMBER: 26382 SUBJECT: LIGO/Virgo S191205ah: MASTER OT 1.5m OSN imaging and 10.4m GTC spectroscopy DATE: 19/12/08 07:13:28 GMT FROM: Alberto J. Castro-Tirado at IAA-CSIC A. F. Valeev (SAO-RAS), Y.-D. Hu, A. J. Castro-Tirado, F. J. Aceituno and E. Fernandez-Garcia (IAA-CSIC), V. Sokolov (SAO-RAS), I. Carrasco and A. Castellon (UMA) and N. Castro-Rodriguez (GRANTECAN, IAC, ULL), on behalf of a larger collaboration, report: Following the detection of MASTER OT J123123.61-043847.2 (Lipunov al. GCNC 26379, Murata et al. GCN 26381) within the error area of the GW event S191205ah (LVC, GCNC 26350), we obtained imaging at the 1.5m OSN telescope in Granada (Spain) and optical spectra covering the range 3700-10000 A with the 10.4m GTC telescope equipped with OSIRIS in La Palma (Spain) starting on Dec 8, 05:20 UT. For MASTER OT J123123.61-043847.2 a magnitude r' = 17.9 on Dec 8, 05:20 UT is derived. The GTC spectrum is consistent with a type Ia SN at redshift z = 0.056 +/- 0.003, implying an absolute optical magnitude close to the expected absolute magnitude at peak of type Ia SNe (M_V = -19.3). Therefore we consider that MASTER OT J123123.61-043847.2 is unrelated to the S191205ah GW alert.