The Candidate Blazar Counterparts of the Ultra-High-Energy Event KM3-230213A

The detection by the KM3NeT experiment of the ultra-high-energy event KM3-230213A marks a milestone in neutrino astrophysics. With an energy estimated at ~ 220 PeV, it is the most energetic cosmic neutrino observed to date, opening the question of its astrophysical origin. Blazars, among the most powerful cosmic accelerators, have been proposed as promising sources of both astrophysical neutrinos and ultra-high-energy cosmic rays. In this contribution, seventeen candidate blazars are identified in the 3° radius error region of KM3-230213A through their multiwavelength signatures. Using archival data and dedicated observations, their properties are characterised throughout the whole electromagnetic spectrum, from radio to gamma rays. Three sources exhibit flaring behaviour in one of the examined bands, in coincidence with the neutrino arrival time. While none of these can be unequivocally associated with the neutrino, the implications of a possible blazar origin of the KM3NeT event are discussed.