Prompt Searches for Very-high-energy <i>γ</i> -Ray Counterparts to IceCube Astrophysical Neutrino Alerts

Abstract The search for sources of high-energy astrophysical neutrinos can be significantly advanced through a multimessenger approach, which seeks to detect the γ -rays that accompany neutrinos as they are produced at their sources. Multimessenger 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 high-energy ( E &gt; 1 GeV) and very-high-energy (VHE; E &gt; 100 GeV) γ -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: follow-up observations of single astrophysical neutrino candidate events (such as IceCube-170922A), and observation of known γ -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 2017 September (after the IceCube-170922A event) and 2021 January. Our study found no associations between γ -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 γ -ray flux.

Publication Details

Journal
The Astrophysical Journal
Published
2026-01-20
DOI
https://doi.org/10.3847/1538-4357/ae2c4e
Primary Topic
Astrophysics and Cosmic Phenomena
Type
article
Field-Weighted Citation Impact
0.00

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article

Prompt Searches for Very-high-energy γ -Ray Counterparts to IceCube Astrophysical Neutrino Alerts

The Astrophysical Journal
Astrophysics and Cosmic Phenomena
article

Prompt Searches for Very-high-energy γ -Ray Counterparts to IceCube Astrophysical Neutrino Alerts

article en

Abstract

Abstract The search for sources of high-energy astrophysical neutrinos can be significantly advanced through a multimessenger approach, which seeks to detect the γ -rays that accompany neutrinos as they are produced at their sources. Multimessenger 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 high-energy ( E &gt; 1 GeV) and very-high-energy (VHE; E &gt; 100 GeV) γ -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: follow-up observations of single astrophysical neutrino candidate events (such as IceCube-170922A), and observation of known γ -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 2017 September (after the IceCube-170922A event) and 2021 January. Our study found no associations between γ -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 γ -ray flux.

The Astrophysical JournalVol. 997(2)
National Science Foundation, Smithsonian Institution, U.S. Department of Energy, National Aeronautics and Space Administration, University of Wisconsin-Madison, Nvidia, Michigan State University, Villum Fonden, Polarforskningssekretariatet, Marquette University, Centres de Recerca de Catalunya, Department of Science and Innovation, South Africa, National Energy Research Scientific Computing Center, European Commission, National Research Foundation, Deutsche Forschungsgemeinschaft, Agence Nationale de la Recherche, Ministry of Education, Culture, Sports, Science and Technology, Schweizerischer Nationalfonds zur Förderung der Wissenschaftlichen Forschung, Universiteit van Amsterdam, Bundesministerium für Bildung und Forschung, Austrian Science Fund, Fonds De La Recherche Scientifique - FNRS, Belgian Federal Science Policy Office, Generalitat de Catalunya, Centre National d’Etudes Spatiales, Eidgenössische Technische Hochschule Zürich, Fonds Wetenschappelijk Onderzoek, Conselho Nacional de Desenvolvimento Científico e Tecnológico, National Research Foundation of Korea, Agenzia Spaziale Italiana, Knut och Alice Wallenbergs Stiftelse, Max-Planck-Gesellschaft, Vetenskapsrådet, Hrvatska Zaklada za Znanost, Fundação Carlos Chagas Filho de Amparo à Pesquisa do Estado do Rio de Janeiro, Centre National de la Recherche Scientifique, Istituto Nazionale di Astrofisica, Commissariat à l'Énergie Atomique et aux Énergies Alternatives, High Energy Accelerator Research Organization, RWTH Aachen University, Université Paris-Saclay, Chiba University, National Commission on Research, Science and Technology, Ministério da Ciência, Tecnologia, Inovações e Comunicações, University of Namibia, Istituto Nazionale di Fisica Nucleare, Bundesministerium für Bildung, Wissenschaft und Forschung, Helmholtz Alliance for Astroparticle Physics, Alliance de recherche numérique du Canada, Instituto de Astrofísica de Canarias, Office of Science, College of Engineering, Michigan State University, Natural Sciences and Engineering Research Council of Canada, Science and Technology Facilities Council, Deutsches Elektronen-Synchrotron, Japan Society for the Promotion of Science, Japan Aerospace Exploration Agency, European Regional Development Fund, Marsden Fund, Agencia Estatal de Investigación, Institut National de Physique Nucléaire et de Physique des Particules, Institute for Cosmic Ray Research, University of Tokyo, Institute for Global Prominent Research, Chiba University, Office of Polar Programs, Office of Advanced Cyberinfrastructure, Office of Experimental Program to Stimulate Competitive Research
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