Characterizing Candidate Blazar Counterparts of the Ultra-high-energy Event KM3-230213A

@article{adriani2026characterizing,
  title = {{Characterizing Candidate Blazar Counterparts of the Ultra-high-energy Event KM3-230213A}},
  author = {O. Adriani and S. Aiello and A. Albert and A. R. Alhebsi and M. Alshamsi and S. Alves Garre and A. Ambrosone and F. Ameli and M. Andre and L. Aphecetche and M. Ardid and S. Ardid and J. Aublin and F. Badaracco and L. Bailly-Salins and Z. Bardačová and B. Baret and A. Bariego-Quintana and Yvonne Becherini and M. Bendahman and Francesca Gualandi and Marouane Benhassi and M Bennani and David M. Benoit and Edward Berbee and E. Berti and Vincent Bertin and P. Betti and S. Biagi and M. Böttcher and Danilo Luigi Bonanno and S. Bottai and A. B. Bouasla and Jihad Boumaaza and Mohammed Bouta and Mieke C. Bouwhuis and C. Bozza and R. M. Bozza and Horea Branzas and F. Bretaudeau and Mischa Breuhaus and R. Bruijn and Jürgen Brunner and Riccardo Bruno and Ernst J. Buis and R. Buompane and Sara Buson and J. Busto and B. Caiffi and David C. Calvo and A. Capone and F. Carenini and V. Carretero and T. Cartraud and Paolo Castaldi and V. Cecchini and S. Celli and L Cerisy and M. Chabab and Andrew W Chen},
  journal = {The Astronomical Journal},
  year = {2026},
  month = aug,
  doi = {10.3847/1538-3881/ae7a4e},
  url = {https://doi.org/10.3847/1538-3881/ae7a4e},
  note = {CC BY 4.0},
}

TY  - JOUR
TI  - Characterizing Candidate Blazar Counterparts of the Ultra-high-energy Event KM3-230213A
AU  - O. Adriani
AU  - S. Aiello
AU  - A. Albert
AU  - A. R. Alhebsi
AU  - M. Alshamsi
AU  - S. Alves Garre
AU  - A. Ambrosone
AU  - F. Ameli
AU  - M. Andre
AU  - L. Aphecetche
AU  - M. Ardid
AU  - S. Ardid
AU  - J. Aublin
AU  - F. Badaracco
AU  - L. Bailly-Salins
AU  - Z. Bardačová
AU  - B. Baret
AU  - A. Bariego-Quintana
AU  - Yvonne Becherini
AU  - M. Bendahman
AU  - Francesca Gualandi
AU  - Marouane Benhassi
AU  - M Bennani
AU  - David M. Benoit
AU  - Edward Berbee
AU  - E. Berti
AU  - Vincent Bertin
AU  - P. Betti
AU  - S. Biagi
AU  - M. Böttcher
AU  - Danilo Luigi Bonanno
AU  - S. Bottai
AU  - A. B. Bouasla
AU  - Jihad Boumaaza
AU  - Mohammed Bouta
AU  - Mieke C. Bouwhuis
AU  - C. Bozza
AU  - R. M. Bozza
AU  - Horea Branzas
AU  - F. Bretaudeau
AU  - Mischa Breuhaus
AU  - R. Bruijn
AU  - Jürgen Brunner
AU  - Riccardo Bruno
AU  - Ernst J. Buis
AU  - R. Buompane
AU  - Sara Buson
AU  - J. Busto
AU  - B. Caiffi
AU  - David C. Calvo
AU  - A. Capone
AU  - F. Carenini
AU  - V. Carretero
AU  - T. Cartraud
AU  - Paolo Castaldi
AU  - V. Cecchini
AU  - S. Celli
AU  - L Cerisy
AU  - M. Chabab
AU  - Andrew W Chen
PY  - 2026
DA  - 2026/08/05
JO  - The Astronomical Journal
DO  - 10.3847/1538-3881/ae7a4e
UR  - https://doi.org/10.3847/1538-3881/ae7a4e
AB  - High-energy astrophysical neutrinos serve as crucial messengers for understanding hadronic acceleration processes and identifying the origins of cosmic rays, with blazars among the most promising neutrino sources. The KM3NeT experiment reported the detection of an ultrahigh-energy neutrino with an energy estimate of ∼220 PeV, the most energetic yet observed. The neutrino arrival direction has a 99% confidence region of 3° radius centered at R.A. 94 . ° 3, decl. −7 . ° 8 (J2000). In this work, 17 candidate blazars located within this region are identified. Comprehensive new observations and archival data analysis for these sources are presented. The study provides a complete multiwavelength coverage across radio, optical, X-ray, and gamma-ray bands, including proprietary data and dedicated follow-up observations. This study highlights flaring behavior in several candidate counterparts. One object exhibits a radio flare coinciding with the neutrino arrival time, with a pre-trial chance probability of 0.26%. Only for this object, the chance probability could be quantified in a robust way. Another candidate displays a rising trend in X-ray flux in a 1 yr window around the neutrino arrival time, while a third undergoes a gamma-ray flare during the same period. Based on the observational findings presented here, while none of these candidates can conclusively be linked to the neutrino, the implications of a possible blazar origin for the KM3NeT event are discussed.
SN  - 0004-6256
SN  - 1538-3881
ER  -