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

KM3NeT Collaboration; MessMapp Group; LAT Collaboration; m Telescope Group; SVOM Collaboration; P. Baldini; J. Buchner; A. K. Erkenov; N. Globus; A. Merloni; A. Paggi; A. V. Popkov; D. Porquet; M. Salvato; Y. V. Sotnikova; P. A. Voitsik

doi:10.3847/1538-3881/ae7a4e

arXiv · 2502.08484

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

KM3NeT Collaboration·MessMapp Group·LAT Collaboration·m Telescope Group·SVOM Collaboration·P. Baldini·J. Buchner·A. K. Erkenov·N. Globus·A. Merloni·A. Paggi·A. V. Popkov·D. Porquet·M. Salvato·Y. V. Sotnikova·P. A. Voitsik

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Abstract

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 ultra-high-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{\deg} radius centered at RA 94.3{\deg}, Dec -7.8{\deg} (J2000). In this work, seventeen 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%. Another candidate displays a rising trend in X-ray flux in a one-year window around the neutrino arrival time, while a third undergoes a gamma-ray flare during the same period. Based on the observational findings here presented, 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.

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KM3NeT Collaboration, MessMapp Group, LAT Collaboration, m Telescope Group, SVOM Collaboration, P. Baldini, J. Buchner, A. K. Erkenov, N. Globus, A. Merloni, A. Paggi, A. V. Popkov, D. Porquet, M. Salvato, Y. V. Sotnikova, P. A. Voitsik. 2025-02-12. Characterizing Candidate Blazar Counterparts of the Ultra-High-Energy Event KM3-230213A. https://doi.org/10.3847/1538-3881/ae7a4e

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