S. Piranomonte (INAF-OAR), P. D'Avanzo, A. Melandri (INAF-OAB), E. Palazzi (INAF-IAFS Bo), M. Branchesi (Urbino University/INFN Pisa), G.Greco (Urbino University/INFN Firenze), P. Astone (INFN-Roma), E. Brocato (INAF-OAR), S. Campana (INAF-OAB), E. Cappellaro (INAF-OAPd), S. Covino (INAF-OAB), F. Getman (INAF-OAC), G. Giuffrida (ASDC), 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), F. Ricci (Sapienza University), G. Stratta (Urbino University/INFN Firenze), V. Testa (INAF-OAR), L. Tomasella (INAF-OAPd), A. Fiorenzano, W. Boschin, D. Carosati (INAF-TNG), on behalf of the INAF Gravitational Astronomy group report:
We report the result of the analysis of the spectrum of the optical transient reported by Rabinowitz et al. (LSQ15bjb; LIGO/Virgo Circular #18473), located in the skymap of the advanced LIGO and Virgo trigger G194575 (Singer et al., LIGO/Virgo Circular #18442) and observed with the 3.6m Italian TNG telescope (Canary Islands, Spain), equipped with DOLORES (D'Avanzo et al. LIGO/Virgo Circular #18476).
Based on a preliminary calibration, the spectrum, obtained on 2015 Oct 26 of 21:59:10 UT, shows that the transient is a supernova of type Ia. The best fit obtained using SNID (Blondin & Tonry 2007, ApJ 666,1024) is with SN 1990N (Mazzali et al. 1993 A&A 269, 423), 6 days days before maximum and placed at a redshift z~0.03. Assuming this redshift, the ejecta expansion velocity measured from the SiII 6355 absorption is about 10900 km/s.