TY - JOUR
T1 - Characterizing Candidate Blazar Counterparts of the Ultra-high-energy Event KM3-230213A
AU - KM3NeT Collaboration
AU - MessMapp Group
AU - Fermi LAT Collaboration
AU - Owens Valley Radio Observatory 40-m Telescope Group
AU - SVOM Collaboration
AU - Adriani, O.
AU - Aiello, S.
AU - Albert, A.
AU - Alhebsi, A. R.
AU - Alshamsi, M.
AU - Alves Garre, S.
AU - Ambrosone, A.
AU - Ameli, F.
AU - Andre, M.
AU - Aphecetche, L.
AU - Ardid, M.
AU - Ardid, S.
AU - Aublin, J.
AU - Badaracco, F.
AU - Bailly-Salins, L.
AU - Bardačová, Z.
AU - Baret, B.
AU - Bariego-Quintana, A.
AU - Becherini, Y.
AU - Bendahman, M.
AU - Benfenati Gualandi, F.
AU - Benhassi, M.
AU - Bennani, M.
AU - Benoit, D. M.
AU - Berbee, E.
AU - Berti, E.
AU - Bertin, V.
AU - Betti, P.
AU - Biagi, S.
AU - Boettcher, M.
AU - Bonanno, D.
AU - Bottai, S.
AU - Bouasla, A. B.
AU - Boumaaza, J.
AU - Bouta, M.
AU - Bouwhuis, M.
AU - Bozza, C.
AU - Bozza, R. M.
AU - Brânzaş, H.
AU - Bretaudeau, F.
AU - Breuhaus, M.
AU - Bruijn, R.
AU - Brunner, J.
AU - Bruno, R.
AU - Buis, E.
AU - Buompane, R.
AU - Bruel, P.
AU - Fegan, S. J.
AU - Horan, D.
AU - Laviron, A.
N1 - Publisher Copyright:
© 2026. The Author(s). Published by the American Astronomical Society. Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.
PY - 2026/9/1
Y1 - 2026/9/1
N2 - 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 (Formula presented) .° 3, decl. −7 (Formula presented) .° 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.
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 (Formula presented) .° 3, decl. −7 (Formula presented) .° 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.
KW - Blazars (164)
KW - High energy astrophysics (739)
KW - Neutrino astronomy (1100)
KW - Neutrino telescopes (1105)
KW - Time domain astronomy (2109)
KW - Ultra-high-energy cosmic radiation (1733)
UR - https://www.scopus.com/pages/publications/105046921357
U2 - 10.3847/1538-3881/ae7a4e
DO - 10.3847/1538-3881/ae7a4e
M3 - Article
AN - SCOPUS:105046921357
SN - 0004-6256
VL - 172
JO - Astronomical Journal
JF - Astronomical Journal
IS - 3
M1 - 139
ER -