TITLE: GCN CIRCULAR NUMBER: 18779 SUBJECT: LIGO/Virgo G211117: LBT Follow-up of iPTF15fen DATE: 15/12/31 06:13:42 GMT FROM: Peter Garnavich at Notre Dame P. Garnavich (Notre Dame) reports: R. Pogge (OSU), J. Turner (UVa), and B. Rothberg (LBTO) obtained LBT/MODS spectra of iPTF15fen (Cenko et al., GCN 18762), the "hostless" candidate at 03:21:37.544 +31:27:08.1 (J2000). Spectra were taken 2015 Dec. 31.1 (UT) and cover 330 nm to 1.0 microns. The r-band acquisition image shows an unresolved source at the position of the iPTF transient. The red Digitized Sky Survey (DSS) image from 1992 also shows this source. The combined spectrum reveals a blue continuum with broad and extremely weak absorption features. The clearest features correspond to Balmer absorption lines of H-beta, H-gamma, and H-delta at low velocity. The source is likely a hydrogen-rich accretion disk in outburst. iPTF15fen is probably a Galactic dwarf nova or a nova-like cataclysmic variable. No narrow emission is detected at the center of the Balmer absorption features as often seen in outbursting disks, but this may be due to the low signal-to-noise ratio of these features.