TITLE: GCN CIRCULAR NUMBER: 16335 SUBJECT: Swift Trigger 600114: Optical spectroscopy from GTC DATE: 14/05/28 07:54:06 GMT FROM: Javier Gorosabel at IAA-CSIC J. Gorosabel (IAA-CSIC/UPV-EHU), A. de Ugarte Postigo (IAA-CSIC/DARK-NBI), C. Thöne (IAA-CSIC), T. Muñoz-Darias (Oxford Uni.), R. Sanchez-Ramirez (IAA-CSIC), R. Scarpa (IAC-ULL), report on behalf of a larger collaboration. We have obtained spectroscopic data of the optical counterpart of the bright X-ray source in M31 (Barthelmy et al. GCNC 16332) with the 10.4m GTC telescope. Observations started on May 28.17800 UT, 6.9 hr post burst. Three 600s spectra where taken with the R1000B grism yielding a spectral range between 3700 and 7700 A at a resolution of ~1000. The slit was positioned within the central light of the globular cluster that is probably associated with the event (FMZ2005-7). A preliminary reduction of the spectra reveals several absorption lines, including Na I, the Balmer series and Ca II, all blue-shifted consistently with the 427 km/s reported by Kang et al. 2012 (ApJS, 199, 37). A very preliminary analysis shows no excess with respect what we would expect from the globular cluster emission. A deeper analysis is ongoing.