2020A&A...640L...4G

The uncertainty region of the highly energetic neutrino IceCube200107A includes 3HSP J095507.9+355101 (z=0.557), an extreme blazar, which was detected in a high, very hard, and variable X-ray state shortly after the neutrino arrival. Following a detailed multiwavelength investigation, we confirm that the source is a genuine BL Lac. This new detection differs from TXS 0506+056, which is thus far the first source associated with IceCube neutrinos, and is considered a "masquerading" BL Lac. As in the case of TXS 0506+056, 3HSP J095507.9+355101 is also way off the so-called blazar sequence. We consider 3HSP J095507.9+355101 a possible counterpart to the IceCube neutrino. Finally, we discuss some theoretical implications in terms of neutrino production.