Spectroscopic lower limit to the redshift (z>0.863) of the BL Lac object 4FGL J2255.1+2411, a possible neutrino source
ATel #13202; Simona Paiano (Universita' dell'Insubria, INAF-OAPD), Paolo Padovani (ESO), Renato Falomo (INAF-OAPD), Paolo Giommi (ASI), Riccardo Scarpa (IAC, Universidad de la Laguna), Aldo Treves (Universita' dell'Insubria, INAF-OABrera)
on 19 Oct 2019; 09:41 UT
Credential Certification: Simona Paiano (simona.paiano@inaf.it)
Subjects: Optical, Gamma Ray, Neutrinos, Blazar
The most significant possible neutrino source found by the ANTARES collaboration is the BL Lac object MG3J225517+2409 associated to the gamma-ray source 4FGLJ2255.1+2411, and also associated with an IceCube high-energy track (Antares collaboration, 2019ICRC,36,840A). A SDSS spectrum obtained in 2013 is dominated by a non thermal continuum with no significant features. The redshift is therefore unknown.
In October 2019, we obtained optical spectroscopy of the object (g = 17.5, r = 17.1) in the 4100-7700 Ang band at the 10.4m GTC+OSIRIS. The spectrum has a S/N ~ 500 and shows the continuum typical of a BL Lac objects and it is available in the database ZBLLAC http://archive.oapd.inaf.it/zbllac/.
We found an absorption doublet identified as MgII 2800 intervening system (the two features are at 5209.8 Ang, EW = 0.37 Ang and at 5223.1 Ang, EW = 0.25 Ang).
We searched for possible intrinsic emission lines (e.g. MgII 2800 and CIV 1540 ) of the source . No lines are found with an upper limit of EW > 0.1 Ang. We conclude that the source is at z >= 0.8633.
At this redshift limit, the absolute magnitude M(UV) < -26.5, and the gamma-ray luminosity L(100MeV-100GeV)> 4x10^46 erg s-1. From our high quality spectrum, we estimated an emission line luminosity upper limit of 1.5x10^41 erg s-1. These values are close to the ones reported for the neutrino source TX0506+056.
ZBLLAC
