Prompt Searches for Very-High-Energy γ-Ray Counterparts to IceCube Astrophysical Neutrino Alerts

J Abhir; A Biland; K Brand; T. Bretz; D Dorner; L Eisenberger; Dominik Elsaesser; P Kaaret; M. J Millard; M Hostert; FACT Collaboration; High Energy Stereoscopic System (H.E.S.S.) Collaboration; MAGIC Collaboration; VERITAS Collaboration; Fermi-LAT Collaboration; IceCube Collaboration

doi:10.48550/arxiv.2512.16562

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Prompt Searches for Very-High-Energy γ-Ray Counterparts to IceCube Astrophysical Neutrino Alerts

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Prompt Searches for Very-High-Energy γ-Ray Counterparts to IceCube Astrophysical Neutrino Alerts

J Abhir, A Biland, K Brand, T. Bretz, D Dorner, L Eisenberger, Dominik Elsaesser, P Kaaret, M. J Millard, M Hostert, …

ArXiv.org

Cornell University

12/18/2025

DOI: 10.48550/arxiv.2512.16562

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Preprint (Author's original)This preprint has not been evaluated by subject experts through peer review. Preprints may undergo extensive changes and/or become peer-reviewed journal articles. Open Access

Abstract

The search for sources of high-energy astrophysical neutrinos can be significantly advanced through a multi-messenger approach, which seeks to detect the gamma rays that accompany neutrinos as they are produced at their sources. Multi-messenger observations have so far provided the first evidence for a neutrino source, illustrated by the joint detection of the flaring blazar TXS 0506+056 in highenergy (HE, E > 1 GeV) and very-high-energy (VHE, E > 100 GeV) gamma rays in coincidence with the high-energy neutrino IceCube-170922A, identified by IceCube. Imaging atmospheric Cherenkov telescopes (IACTs), namely FACT, H.E.S.S., MAGIC, and VERITAS, continue to conduct extensive neutrino target-of-opportunity follow-up programs. These programs have two components: followup observations of single astrophysical neutrino candidate events (such as IceCube-170922A), and observation of known gamma-ray sources after the identification of a cluster of neutrino events by IceCube. Here we present a comprehensive analysis of follow-up observations of high-energy neutrino events observed by the four IACTs between September 2017 (after the IceCube-170922A event) and January 2021. Our study found no associations between gamma-ray sources and the observed neutrino events. We provide a detailed overview of each neutrino event and its potential counterparts. Furthermore, a joint analysis of all IACT data is included, yielding combined upper limits on the VHE gamma-ray flux.

Physics - High Energy Astrophysical Phenomena

Details

Title: Subtitle: Prompt Searches for Very-High-Energy γ-Ray Counterparts to IceCube Astrophysical Neutrino Alerts
Creators: J Abhir - ETH Zurich
A Biland - ETH Zurich
K Brand - University of Würzburg
T. Bretz - ETH Zurich
D Dorner - University of Würzburg
L Eisenberger
Dominik Elsaesser
P Kaaret
M. J Millard
M Hostert
FACT Collaboration
High Energy Stereoscopic System (H.E.S.S.) Collaboration
MAGIC Collaboration
VERITAS Collaboration
Fermi-LAT Collaboration
IceCube Collaboration
Resource Type: Preprint
Publication Details: ArXiv.org
DOI: 10.48550/arxiv.2512.16562
ISSN: 2331-8422
Publisher: Cornell University; Ithaca, New York
Language: English
Date posted: 12/18/2025
Academic Unit: Physics and Astronomy
Record Identifier: 9985093923802771

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