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We report on multiwavelength studies of the blazar NVSS J171822+423948, whichis identified as the low-energy counterpart of 4FGL J1718.5+4237, the onlygamma-ray source known to be cospatial with the IceCube neutrino eventIC-201221A. After a 12-year long quiescent period undetected by Fermi-LAT,gamma-ray activities with a tenfold flux increase emerge soon (a few tens ofdays) after arrival of the neutrino. Associated optical flares in the ZTF $g$,$r$, and $i$ bands are observed together with elevated WISE infrared fluxes.Synchronized variations suggest that both the gamma-ray emission and theneutrino event are connected to the blazar. Furthermore, the optical spectrumreveals emission lines at a redshift $z$ = 2.68 $\pm$ 0.01. Thus, it is thefirst candidate for a neutrino-emitting blazar at the redshift above 2.Discussions of theoretical constraints of neutrino production and comparisonswith other candidates are presented.

Awakening of A Blazar at Redshift 2.7 Temporally Coincident with Arrival of Cospatial Neutrino Event IceCube-201221A