Prompt Searches for Very-high-energy γ-Ray Counterparts to IceCube Astrophysical Neutrino Alerts J. Abhir, A. Biland, K. Brand, T. Bretz, D. Dorner, et al. Astrophysical Journal, 2026 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 > 1 GeV) and very-high-energy (VHE; E > 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.
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Modelling of highly extended Gamma-ray emission around the Geminga Pulsar as detected with H.E.S.S. Proceedings of Science, 2024
Target of Opportunity observations of flaring blazars with H.E.S.S. Proceedings of Science, 2024
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Search for dark matter annihilation line signals with the H.E.S.S. Inner Galaxy Survey Proceedings of Science, 2024
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Joint H.E.S.S. and Fermi-LAT analysis of the region around PSR J1813-1749 Proceedings of Science, 2024
Multiwavelength Observations of the Blazar PKS 0735+178 in Spatial and Temporal Coincidence with an Astrophysical Neutrino Candidate IceCube-211208A Proceedings of Science, 2024
Joint searches by FACT, H.E.S.S., MAGIC and VERITAS for VHE gamma-ray emission associated with neutrinos detected by IceCube Proceedings of Science, 2024
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Expected performance of the ALTO particle detector array designed for 200 GeV - 50 TeV gamma-ray astronomy Proceedings of Science, 2022
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The young massive stellar cluster Westerlund 1 in γ rays as seen with H.E.S.S. Proceedings of Science, 2022
Detection of extended TeV emission around the Geminga pulsar with H.E.S.S. Proceedings of Science, 2022
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Detection of new Extreme BL Lac objects with H.E.S.S. and Swift XRT Proceedings of Science, 2022
Is PKS 0625−354 another variable TeV active galactic nucleus? Proceedings of Science, 2022
LMC N132D: a mature supernova remnant with a youthful gamma-ray spectrum Proceedings of Science, 2022
Evidence of 100 TeV γ-ray emission from HESS J1702-420: A new PeVatron candidate Proceedings of Science, 2022
Limits on primordial black hole evaporation from H.E.S.S. observations Proceedings of Science, 2022
Science verification of the new FlashCam-based camera in the 28 m telescope of H.E.S.S. Proceedings of Science, 2022
Revisiting the PeVatron candidate MGRO J1908+06 with an updated H.E.S.S. analysis Proceedings of Science, 2022
Deep observations of Kepler's SNR with H.E.S.S. Proceedings of Science, 2022
Observation of burst activity from SGR1935+2154 associated to first galactic FRB with H.E.S.S. Proceedings of Science, 2022
H.E.S.S. ToO program on nearby core-collapse Supernovae: search for very-high energy γ-ray emission towards the SN candidate AT2019krl in M74 Proceedings of Science, 2022
Search for dark matter annihilation signals from the Galactic Center with the H.E.S.S. Inner Galaxy Survey Proceedings of Science, 2022
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Search for dark matter annihilation signals from unidentified Fermi-LAT objects with H.E.S.S. Proceedings of Science, 2022
Astronomy outreach in Namibia: H.E.S.S. and beyond Proceedings of Science, 2022
Combined dark matter searches towards dwarf spheroidal galaxies with Fermi-LAT, HAWC, H.E.S.S., MAGIC, and VERITAS Proceedings of Science, 2022
Prompt Searches for Very-High-Energy {\gamma}-Ray Counterparts to IceCube Astrophysical Neutrino Alerts J Abhir, A Biland, K Brand, T Bretz, D Dorner, L Eisenberger, D Elsaesser, ... arXiv preprint arXiv:2512.16562 , 2025 2025
arXiv: Prompt Searches for Very-High-Energy γ-Ray Counterparts to IceCube Astrophysical Neutrino Alerts J Abhir, P Koundal, N van Eijndhoven, N Krieger, M Chernyakova, ... Astrophys. J. , 2025 2025
Blazars as a Potential Origin of the KM3-230213A Event O Adriani, A Albert, AR Alhebsi, S Alshalloudi, SA Garre, A Ambrosone, ... 2025 Citations: 1
Fifteen years of Gamma-Ray Burst observations at Very High Energies with HESS E Ruiz-Velasco, C Arcaro, M de Lavergne, Z Huang, D Sanchez, ... arXiv preprint arXiv:2509.15869 , 2025 2025
Detecting Energetic Bursts In Very-High-Energy Gamma Rays: Analysis methods to increase the population of extragalactic transients in very-high-energy gamma rays using ALTO … M Senniappan Linnaeus University Press , 2025 2025
Searching for gamma-ray counterparts of FRBs with HESS A Jaitly, H Ashkar, F Bradascio, D Kostunin, G Rowell, F Schüssler, ... 38th International Cosmic Ray Conference (ICRC2023)-Gamma-ray Astronomy (GA … , 2024 2024
Monitoring the first candidate host for the merger of a Supermassive Black Hole Binary with HESS F Aharonian, F Ait-Benkhali, A Alkan, J Aschersleben, H Ashkar, ... 38th International Cosmic Ray Conference, 688 , 2024 2024 Citations: 1
Probing the morphology of the low state gamma-ray emission of M87 with HESS C Arcaro, N Mathieu, F Aharonian, F Ait-Benkhali, A Alkan, ... 38th International Cosmic Ray Conference, 696 , 2024 2024 Citations: 3
An updated view of the VHE gamma-ray sky around the stellar cluster Westerlund 2 with the HESS experiment TL Holch, F Aharonian, F Ait-Benkhali, A Alkan, J Aschersleben, H Ashkar, ... 38th International Cosmic Ray Conference, 778 , 2024 2024 Citations: 1
Joint searches by FACT, HESS, MAGIC and VERITAS for VHE gamma-ray emission associated with neutrinos detected by IceCube F Schüssler, H Ashkar, E Bernardini, A Berti, F Bradascio, S Buson, ... arXiv preprint arXiv:2309.15469 , 2023 2023 Citations: 6
Sensitivity to point-like sources of the ALTO atmospheric particle detector array, designed for 200 GeV–50 TeV γ-ray astronomy M Punch, M Senniappan, Y Becherini, GK Mezek, S Thoudam, T Bylund, ... Journal of High Energy Astrophysics 39, 1-13 , 2023 2023
Search for dark matter annihilation signals in the HESS inner galaxy survey H Abdalla, F Aharonian, FA Benkhali, EO Angüner, C Armand, H Ashkar, ... Physical Review Letters 129 (11), 111101 , 2022 2022 Citations: 167
Time-resolved hadronic particle acceleration in the recurrent nova RS Ophiuchi HESS Collaboration*†, F Aharonian, F Ait Benkhali, EO Angüner, ... Science 376 (6588), 77-80 , 2022 2022 Citations: 121
HESS ToO program on nearby core-collapse Supernovae: search for very-high energy γ-ray emission towards the SN candidate AT2019krl in M74 HESS Collaboration Proceedings of Science 395, 809 , 2022 2022
HESS follow-up of BBH merger events H Collabortion, M Arroyo Seglar, H Abdalla, F Aharonian, F Ait-Benkhali, ... 37th International Cosmic Ray Conference (ICRC2021) , 2022 2022
Search for TeV emission from the Fermi Bubbles at low Galactic latitudes with HESS inner Galaxy survey H Abdalla, F Aharonian, F Ait-Benkhali, O Anguener, C Arcaro, C Armand, ... 37th International Cosmic Ray Conference, 791 , 2022 2022
Searching for VHE gamma-ray emission associated with IceCube neutrino alerts using FACT, HESS, MAGIC, and VERITAS S Ansoldi, LA Antonelli, A Arbet Engels, M Artero, K Asano, D Baack, ... arXiv preprint arXiv:2109.04350 , 2022 2022
Revealing time-resolved particle acceleration in the recurrent Nova RS Ophiuchi F Aharonian, F Ait Benkhali, EO Angüner, H Ashkar, M Backes, ... arXiv e-prints, arXiv: 2202.08201 , 2022 2022
HESS ToO program on nearby core-collapse Supernovae: search for very-high energy γ-ray emission towards the SN candidate AT2019krl in M74 H Abdalla, F Aharonian, F Ait-Benkhali, O Anguener, C Arcaro, C Armand, ... 2022
Is PKS 0625-354 another variable TeV active galactic nucleus? H Abdalla, F Aharonian, F Ait-Benkhali, O Anguener, C Arcaro, C Armand, ... 2022
MOST CITED SCHOLAR PUBLICATIONS
A very-high-energy component deep in the γ-ray burst afterglow H Abdalla, R Adam, F Aharonian, F Ait Benkhali, EO Angüner, M Arakawa, ... Nature 575 (7783), 464-467 , 2019 2019 Citations: 439
Revealing x-ray and gamma ray temporal and spectral similarities in the GRB 190829A afterglow HESS collaboration, H Abdalla, F Aharonian, F Ait Benkhali, EO Angüner, ... Science 372 (6546), 1081-1085 , 2021 2021 Citations: 248
Search for dark matter annihilation signals in the HESS inner galaxy survey H Abdalla, F Aharonian, FA Benkhali, EO Angüner, C Armand, H Ashkar, ... Physical Review Letters 129 (11), 111101 , 2022 2022 Citations: 167
Broadband multi-wavelength properties of M87 during the 2017 Event Horizon Telescope campaign JC Algaba, J Anczarski, K Asada, M Baloković, S Chandra, YZ Cui, ... The Astrophysical Journal Letters 911 (1), L11 , 2021 2021 Citations: 140
Time-resolved hadronic particle acceleration in the recurrent nova RS Ophiuchi HESS Collaboration*†, F Aharonian, F Ait Benkhali, EO Angüner, ... Science 376 (6588), 77-80 , 2022 2022 Citations: 121
The 2014 TeV γ-ray flare of Mrk 501 seen with HESS: temporal and spectral constraints on Lorentz invariance violation H Abdalla, F Aharonian, F Ait Benkhali, EO Angüner, M Arakawa, ... The Astrophysical Journal 870 (2), 93 , 2019 2019 Citations: 111
Particle transport within the pulsar wind nebula HESS J1825–137 H Abdalla, F Aharonian, F Ait Benkhali, EO Angüner, M Arakawa, ... Astronomy & Astrophysics 621, A116 , 2019 2019 Citations: 101
Resolving acceleration to very high energies along the jet of Centaurus A Nature 582 (7812), 356-359 , 2020 2020 Citations: 98
First ground-based measurement of sub-20 GeV to 100 GeV γ-Rays from the Vela pulsar with HESS II H Abdalla, F Aharonian, F Ait Benkhali, EO Angüner, M Arakawa, ... Astronomy & Astrophysics 620, A66 , 2018 2018 Citations: 90
Searches for gamma-ray lines and ‘pure WIMP’spectra from Dark Matter annihilations in dwarf galaxies with HESS M Cirelli, P Panci, F Sala, J Silk, M Taoso, H Abdalla, F Aharonian, ... Journal of cosmology and astroparticle physics 2018 (11), 037 , 2018 2018 Citations: 81
Search for dark matter signals towards a selection of recently detected DES dwarf galaxy satellites of the Milky Way with HESS H Abdallah, R Adam, F Aharonian, F Ait Benkhali, EO Angüner, ... Physical Review D 102 (6), 062001 , 2020 2020 Citations: 76
The starburst galaxy NGC 253 revisited by HESS and Fermi-LAT H Abdalla, F Aharonian, F Ait Benkhali, EO Angüner, M Arakawa, ... Astronomy & Astrophysics 617, A73 , 2018 2018 Citations: 67
Resolving the Crab pulsar wind nebula at teraelectronvolt energies Nature astronomy 4 (2), 167-173 , 2020 2020 Citations: 66
HESS and MAGIC observations of a sudden cessation of a very-high-energy γ-ray flare in PKS 1510− 089 in May 2016 H Abdalla, R Adam, F Aharonian, F Ait Benkhali, EO Angüner, C Arcaro, ... Astronomy & astrophysics 648, A23 , 2021 2021 Citations: 48
Constraints on the emission region of 3C 279 during strong flares in 2014 and 2015 through VHE γ-ray observations with HESS H Abdalla, R Adam, F Aharonian, F Ait Benkhali, EO Angüner, M Arakawa, ... Astronomy & Astrophysics 627, A159 , 2019 2019 Citations: 44
Evidence of 100 TeV γ-ray emission from HESS J1702-420: A new PeVatron candidate H Abdalla, F Aharonian, F Ait Benkhali, EO Angüner, C Arcaro, C Armand, ... Astronomy & Astrophysics 653, A152 , 2021 2021 Citations: 43
Detection of very-high-energy γ-ray emission from the colliding wind binary η Car with HESS H Abdalla, R Adam, F Aharonian, F Ait Benkhali, EO Angüner, M Arakawa, ... Astronomy & Astrophysics 635, A167 , 2020 2020 Citations: 36
HESS and Fermi-LAT observations of PSR B1259–63/LS 2883 during its 2014 and 2017 periastron passages H Abdalla, R Adam, F Aharonian, F Ait Benkhali, EO Angüner, M Arakawa, ... Astronomy & Astrophysics 633, A102 , 2020 2020 Citations: 36
HESS and Suzaku observations of the Vela X pulsar wind nebula H Abdalla, F Aharonian, F Ait Benkhali, EO Angüner, M Arakawa, ... Astronomy & Astrophysics 627, A100 , 2019 2019 Citations: 35
HESS detection of very high-energy γ-ray emission from the quasar PKS 0736+ 017 H Abdalla, R Adam, F Aharonian, F Ait Benkhali, EO Angüner, M Arakawa, ... Astronomy & Astrophysics 633, A162 , 2020 2020 Citations: 34
