On the redshift of the BL Lac neutrino candidate 4C+41.11 (3FHLJ0423.8+4149)

ATel #12802; Simona Paiano (FINCA - University of Turku, INAF-OAPD), Renato Falomo (INAF-OAPD), Aldo Treves (Università degli Studi dell’Insubria, OA-Brera), Chiara Righi (OA-Brera), Riccardo Scarpa (IAC, Universidad de La Laguna), Elina Lindfors (FINCA - University of Turku)
on 24 May 2019; 13:14 UT
Credential Certification: Simona Paiano (simona.paiano@inaf.it)

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4C+41.11 is a peculiar BL Lac object characterised by a low synchrotron peak frequency that is located in the proximity to a well reconstructed neutrino event (Righi et al. 2018). The source is at low galactic latitude (b = -5.4 degrees) and it is severely absorbed (E(B-V)=0.6). We obtained an optical spectrum of the source (R~19.5) at the 10.4m Gran Telescopio Canarias using OSIRIS (exposure time = 3600 sec and spectral range = 4800-9000 Ang). The observed spectrum is characterised by the a power-law emission (spectral index = -0.6). We detect a single emission line at 6997.6 Ang of equivalent width EW = 1.9 Ang. The most plausible identification of this line is [OIII] (5007 Ang) that yields a tentative redshift of z = 0.397. The component of [OIII] doublet (4959 Ang) is washed out by the telluric band at 6870 Ang. The optical spectrum is reported in our online ZBLLAC database (http://www.oapd.inaf.it/zbllac/). At this redshift the Fermi-LAT gamma-ray luminosity, in the 100 MeV to 100 GeV range, is ~1.5x10^46 erg s-1, comparable to that of TXS0506+056.

ZBLLAC