The second H.E.S.S. gamma-ray burst catalogue: 15 years of observations with the H.E.S.S. telescopes

¹ University of Southern Denmark, Campusvej 55, 5230 Odense M, Denmark
² Astronomy & Astrophysics Section, School of Cosmic Physics, Dublin Institute for Advanced Studies, DIAS Dunsink Observatory, Dublin D15 XR2R, Ireland
³ Max-Planck-Institut für Kernphysik, P.O. Box 103980, D 69029 Heidelberg, Germany
⁴ Laboratoire Leprince-Ringuet, École Polytechnique, CNRS, Institut Polytechnique de Paris, F-91128, Palaiseau, France
⁵ University of Namibia, Department of Physics, Private Bag 13301, Windhoek, 10005 Namibia
⁶ Centre for Space Research, North-West University, Potchefstroom, 2520 South Africa
⁷ Deutsches Elektronen-Synchrotron DESY, Platanenallee 6, 15738, Zeuthen, Germany
⁸ Institut für Physik und Astronomie, Universität Potsdam, Karl-Liebknecht-Strasse 24/25, D 14476 Potsdam, Germany
⁹ Université Paris Cité, CNRS, Astroparticule et Cosmologie, F-75013, Paris, France
¹⁰ Linnaeus University Sweden, Universitetsplatsen 1, 352 52 Växjö, Sweden
¹¹ Institut für Physik, Humboldt-Universität zu Berlin, Newtonstr. 15, D 12489 Berlin, Germany
¹² LUX, Observatoire de Paris, Université PSL, CNRS, Sorbonne Université, 5 Pl. Jules Janssen, 92190 Meudon, France
¹³ Sorbonne Université, CNRS/IN2P3, Laboratoire de Physique Nucléaire, et de Hautes Energies, LPNHE, 4 place Jussieu, 75005 Paris, France
¹⁴ IRFU, CEA, Université Paris-Saclay, F-91191, Gif-sur-Yvette, France
¹⁵ Friedrich-Alexander-Universität Erlangen-Nürnberg, Erlangen Centre for Astroparticle Physics, Nikolaus-Fiebiger-Str. 2, 91058 Erlangen, Germany
¹⁶ Instytut Fizyki Jdrowej PAN, ul. Radzikowskiego 152, ul. Radzikowskiego 152, 31-342, Kraków, Poland
¹⁷ School of Physics, University of the Witwatersrand, 1 Jan Smuts Avenue, Braamfontein, Johannesburg 2050, South Africa
¹⁸ School of Physical Sciences and Centre for Astrophysics & Relativity, Dublin City University, Glasnevin, Dublin D09 W6Y4, Ireland
¹⁹ University of Oxford, Department of Physics, Denys Wilkinson Building, Keble Road, Oxford, OX1 3RH, UK
²⁰ Aix Marseille Université, CNRS/IN2P3, CPPM, Marseille, France
²¹ Laboratoire Univers et Particules de Montpellier, Université Montpellier, CNRS/IN2P3, CC 72, Place Eugène Bataillon F-34095, Montpellier Cedex 5, France
²² School of Science, Western Sydney University, Locked Bag 1797, Penrith South DC NSW 2751, Australia
²³ Université Bordeaux, CNRS, LP2I Bordeaux, UMR 5797, F-33170, Gradignan, France
²⁴ Institut für Astronomie und Astrophysik, Universität Tübingen, Sand 1 D 72076, Tübingen, Germany
²⁵ Universität Innsbruck, Institut für Astro- und Teilchenphysik, Technikerstraße 25 6020, Innsbruck, Austria
²⁶ Universität Hamburg, Institut für Experimentalphysik, Luruper Chaussee 149 D 22761, Hamburg, Germany
²⁷ Obserwatorium Astronomiczne, Uniwersytet Jagielloński, ul. Orla 171 30-244, Kraków, Poland
²⁸ Landessternwarte, Universität Heidelberg, Königstuhl, D 69117, Heidelberg, Germany
²⁹ Institute of Astronomy, Faculty of Physics, Astronomy and Informatics, Nicolaus Copernicus University, Grudziadzka 5 87-100, Torun, Poland
³⁰ Nicolaus Copernicus Astronomical Center, Polish Academy of Sciences, ul. Bartycka 18 00-716, Warsaw, Poland
³¹ School of Physical Sciences, University of Adelaide, Adelaide 5005, Australia
³² University of Leicester, School of Physics and Astronomy, University Road Leicester LE1 7RH, United Kingdom
³³ Yerevan Physics Institute, 2 Alikhanian Brothers St. 0036, Yerevan, Armenia
³⁴ Department of Physics, Konan University, 8-9-1 Okamoto, Higashinada Kobe, Hyogo 658-8501, Japan
³⁵ Kapteyn Astronomical Institute, University of Groningen, Landleven 12 9747 AD, Groningen, The Netherlands
³⁶ GRAPPA, Anton Pannekoek Institute for Astronomy, University of Amsterdam, Science Park 904 1098 XH Amsterdam, The Netherlands
³⁷ Laboratoire d’Annecy De Physique Des Particules (LAPP), CNRS, 9 Chem. de Bellevue 74940 Annecy, France
³⁸ Scuola Internazionale Superiore di Studi Avanzati (SISSA), Via Bonomea 265 I-34136, Trieste, Italy
³⁹ INFN Sezione di Padova, Via Marzolo 8 35131 Padova, Italy

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Received: 13 June 2025
Accepted: 8 January 2026

Abstract

Context. Recent observational efforts using imaging atmospheric Cherenkov telescopes (IACTs) have led to firm detections of very-high-energy (VHE) signals from bright gamma-ray bursts (GRBs), often at moderate redshifts.

Aims. This work presents 15 years of H.E.S.S. GRB observations and examines their implications through population comparisons and selected modelling cases.

Methods. GRBs are a key science target of the High Energy Stereoscopic System (H.E.S.S.). With a low-energy threshold (≲100 GeV) and rapid repointing capabilities, H.E.S.S. can begin follow-up observations within tens of seconds after a GRB trigger, covering the late prompt or early afterglow phases.

Results. We report GRB follow-up observations with H.E.S.S. from 2004 to 2019, which resulted in no significant VHE signals (aside from the detections of GRB 180720B and GRB 190829A). The resulting upper limits comprise the largest set available for GRBs at VHE.

Conclusions. A subset of bursts with favourable conditions were selected for X-ray analysis and emission modelling. Population studies were performed to compare detected and non-detected GRBs. The results indicate that VHE-detected GRBs are not a distinct population, but tend to feature luminous X-ray emission and favourable redshift and observing conditions. This highlights the potential of next-generation IACTs such as the Cherenkov Telescope Array Observatory (CTAO), whose lower energy threshold will enhance the detection of fainter and more distant GRBs.