TITLE:   GCN CIRCULAR
NUMBER:  19145
SUBJECT: LIGO/Virgo G211117: GRAWITA LBT follow-up of PS15dpn
DATE:    16/03/04 17:34:54 GMT
FROM:    Enzo Brocato at INAF-OA Roma  <enzo.brocato@oa-roma.inaf.it>

E. Palazzi (INAF-IASF Bo),  E. Cappellaro (INAF-OAPd), E. Brocato (INAF-OAR), M. Branchesi (Urbino . University/INFN Firenze), S. Covino (INAF-OAB), A. Grado (INAF-OAC), E. Pian (SNS-Pisa), F. Cusano (INAF-OABo), A. Marchetti (INAF-IASF Mi), A. Rossi , L.Amati (INAF-IASF Bo), L. A. Antonelli (INAF-OAR),  S. Campana,  P. D'Avanzo (INAF-OAB), V. D'Elia (INAF-ASDC), F. Getman (INAF-OAC), G. Giuffrida (INAF-ASDC), G.Greco (Urbino University/INFN Firenze), L. Limatola (INAF-OAC), M. Lisi (INAF-OAR), S. Marinoni, P.  Marrese (INAF-ASDC),  A. Melandri (INAF-OAB), L. Nicastro (INAF-IASF Bo), S. Piranomonte (INAF-OAR), L. Pulone (INAF-OAR), G. Stratta (Urbino University/INFN Firenze), G. Tagliaferri (INAF-OAB), V. Testa (INAF-OAR), L. Tomasella (INAF-OAPd) on behalf of the GRAvitational Wave Inaf TeAM (GRAWITA).

Further to GCN 18786 and GCN 18811, we report the spectroscopic classification of the Pan-STARRS transient PS15dpn within the localisation region of G211117. 
LBT/MODS and LBT/LUCI spectra were taken on 2016 Jan 28-29 and cover 320 nm to 1.0 microns the MODS optical spectra, 1.0 to 2-3 microns the LUCI infrared spectra.
Multiband LBT/LBC (UBVr) photometric observations were performed simultaneously with the infrared spectroscopy.  

The transient and its host galaxy are very well detected in both photometric and spectroscopic data.

The redshift of the host galaxy measured from narrow H_alpha, NII and OII emission lines  is z=0.1749.
Based on a preliminary calibration, the spectra show that the transient is a peculiar supernova of type Ibn similar to SN 2006jc few weeks after maximum (Pastorello et al. 2008, MNRAS 389,113).
Indeed there appear strong HeI emission lines (in particular the 501.6, 587.5, 706.5 nm transitions) of moderate width (FWHM< ~3000 km/s). In the near infrared two emissions are measured at ~1090 nm and  1280 nm likely due to MgII 933-934 nm and  He I 1083nm.