TITLE: GCN CIRCULAR NUMBER: 20408 SUBJECT: LIGO/Virgo G268556/GW170104: TNG spectroscopic observations of iPTF17ck and iPTF17dz DATE: 17/01/09 17:44:47 GMT FROM: Paolo D'Avanzo at INAF-OAB P. D'Avanzo (INAF-OAB), L. Tomasella, E. Cappellaro (INAF-OAPD), S. Piranomonte (INAF-OAR), A. Melandri (INAF-OAB), V. D'Elia (INAF-ASDC), G. Greco (Urbino University/INFN Firenze), G. Stratta (Urbino University/INFN Firenze), S. Ascenzi (INAF-OAR), M.T. Botticella (INAF-OAC), E. Palazzi (INAF-IAFS Bo), A. Rossi (INAF-IASF Bo), S. Covino (INAF-OAB), L.Amati (INAF-IASF Bo), L. A. Antonelli, (INAF-OAR), M. Branchesi (Urbino University/INFN Firenze), S. Campana (INAF-OAB), F. Getman (INAF-OAC), A. Grado (INAF-OAC), L. Limatola (INAF-OAC), M. Lisi (INAF-OAR), L. Nicastro (INAF-IASF Bo), E. Pian (SNS-Pisa), L. Pulone (INAF-OAR), G. Tagliaferri (INAF-OAB), V. Testa (INAF-OAR), S. Yang (INAF-OAPD), E. Brocato (INAF-OAR), L. Di Fabrizio, G. Mainella (INAF/TNG) on behalf of GRavitational Wave Inaf TeAm report: We observed the transients iPTF17ck and iPTF17dz (Kasliwal et al., LVC GCN 20398) with the TNG 3.6m telescope located in Canary Islands equipped with the DOLORES camera in spectroscopic mode. The observations were carried out between 2017-01-09.1044 UT and 2017-01-09.1797 UT. The iPTF17ck spectrum is consistent with a Seyfert galaxy. We detect prominent emission features consistent with [OII], Hdelta, Hgamma, Hbeta, [OIII], Halpha at a common redshift z~0.122 (broadly consistent with the photometric redshift of this galaxy reported in SDSS-DR13: z=0.169 +/- 0.034). We cannot identify any contribution from the optical transient in the spectrum, nor in the acquisition image. The iPTF17dz spectrum shows that this transient is a normal SN of type Ia about 1 week before maximum at a redshift z~0.092 (that is smaller than the photometric redshift of this galaxy reported in SDSS-DR13: z=0.235 +/- 0.085). The classification was performed using the GELATO (Harutyunyan et al. 2008, A&A, 488, 383) and SNID (Blondin and Tonry 2007, ApJ, 666, 1024) tools. [GCN OPS NOTE(10jan17): Per author's request, all the SN name references were changed from '16' to '17'.]