PAIANO, SimonaSimonaPAIANOFALOMO, RenatoRenatoFALOMOTreves, AldoAldoTrevesScarpa, RiccardoRiccardoScarpa2021-02-112021-02-1120182041-8205http://hdl.handle.net/20.500.12386/30325The bright BL Lac object TXS 0506+056 is the most likely counterpart of the IceCube neutrino event EHE 170922A. The lack of this redshift prevents a comprehensive understanding of the modeling of the source. We present high signal-to-noise optical spectroscopy, in the range 4100-9000 Å, obtained at the 10.4 m Gran Telescopio Canarias. The spectrum is characterized by a power-law continuum and is marked by faint interstellar features. In the regions unaffected by these features, we found three very weak (EW ∼ 0.1 Å) emission lines that we identify with [O II] 3727 Å, [O III] 5007 Å, and [N II] 6583 Å, yielding the redshift z = 0.3365 ± 0.0010.STAMPAenArticle10.3847/2041-8213/aaad5e2-s2.0-85047749180000426055900005https://iopscience.iop.org/article/10.3847/2041-8213/aaad5e2018ApJ...854L..32PFIS/05 - ASTRONOMIA E ASTROFISICA