TITLE: GCN CIRCULAR NUMBER: 25721 SUBJECT: LIGO/Virgo S190910d: AT2019pvu, AT2019pvv, AT2019pvz and AT2019pwa 10.4m GTC spectroscopy DATE: 19/09/10 23:31:49 GMT FROM: Alberto J. Castro-Tirado at IAA-CSIC A. J. Castro-Tirado (IAA-CSIC), A. F. Valeev and V. V. Sokolov (SAO-RAS), Y.-D. Hu and E. Fernandez-Garcia (IAA-CSIC), I. Carrasco and A. Castellon (UMA) and J. Font Serra (GRANTECAN, IAC, ULL), on behalf of a larger collaboration, report: Following the detection of ZTF19abyfhov/AT2019pvu, ZTF19abyfhaq/AT2019pvv, ZTF19abyfbii/AT2019pvz and ZTF19abyfazm/AT2019pwa (Anand et al., GCN 25706) within the error area of the GW event S190910d (LVC, GCNC 25695), we obtained imaging and optical spectra covering the range 3700-10000 A with the 10.4m GTC telescope equipped with OSIRIS in La Palma (Spain) starting on Sep 10, 20:25 UT. For AT2019pvu, a magnitude r = 20.33 +/- 0.05 on Sep 10, 20:58 UT is derived. Cross-correlating the transient spectrum (broad lines) with supernova template spectra in SNID (Blondin & Tonry, 2007), we find a good match to the spectra of SNIa at redshift z = 0.133 +/- 0.001. For AT2019pvv, a magnitude r = 21.08 +/- 0.05 on Sep 10, 22:14 UT is derived. The spectrum shows a faint H-alpha line in emission at z = 0 but the low S/N ratio prevents a more precise classification at this stage. For AT2019pvz, a magnitude r = 20.26 +/- 0.05 on Sep 10, 20:27 UT is derived. The spectrum is consistent with that of a SN Ia at the nearby host galaxy redshift z = 0.1286 +/- 0.0005 (based on H-alpha, H-beta, [O III] and others narrow emission lines). For AT2019pwa, a magnitude r = 18.38 +- 0.03 on Sep 10, 21:31 UT is derived. The spectrum displays a blue continuum with the Ca II H&K 3934 A and 3969 A doublet in absorption at z = 0 being the only clear features, which supports the object being a cataclysmic variable in our Galaxy, in agreement with Perley and Copperwheat (GCNC 25720). Therefore we consider ZTF19abyfhov/AT2019pvu, ZTF19abyfhaq/AT2019pvv, ZTF19abyfbii/AT2019pvz and ZTF19abyfazm/AT2019pwa to be unrelated to the GW event S190910d.