A new method of reconstructing images of gamma-ray telescopes applied to the LST-1 of CTAO

¹ Department of Physics, Tokai University, 4-1-1, Kita-Kaname, Hiratsuka, Kanagawa 259-1292, Japan
² Institute for Cosmic Ray Research, University of Tokyo, 5-1-5, Kashiwa-no-ha, Kashiwa, Chiba 277-8582, Japan
³ INFN and Università degli Studi di Siena, Dipartimento di Scienze Fisiche, della Terra e dell’Ambiente (DSFTA), Sezione di Fisica, Via Roma 56, 53100 Siena, Italy
⁴ Université Paris-Saclay, Université Paris Cité, CEA, CNRS, AIM, 91191 Gif-sur-Yvette Cedex, France
⁵ FSLAC IRL 2009, CNRS/IAC, La Laguna, Tenerife, Spain
⁶ Departament de Física Quàntica i Astrofísica, Institut de Ciències del Cosmos, Universitat de Barcelona, IEEC-UB, Martí i Franquès, 1, 08028 Barcelona, Spain
⁷ Instituto de Astrofísica de Andalucía-CSIC, Glorieta de la Astronomía s/n, 18008 Granada, Spain
⁸ Department of Astronomy, University of Geneva, Chemin d’Ecogia 16, 1290 Versoix, Switzerland
⁹ IPARCOS-UCM, Instituto de Física de Partículas y del Cosmos, and EMFTEL Department, Universidad Complutense de Madrid, Plaza de Ciencias, 1. Ciudad Universitaria, 28040 Madrid, Spain
¹⁰ INFN Sezione di Napoli, Via Cintia, ed. G, 80126 Napoli, Italy
¹¹ INAF – Osservatorio Astronomico di Roma, Via di Frascati 33, 00040 Monteporzio Catone, Italy
¹² Max-Planck-Institut für Physik, Föhringer Ring 6, 80805 München, Germany
¹³ INFN Sezione di Padova and Università degli Studi di Padova, Via Marzolo 8, 35131 Padova, Italy
¹⁴ Univ. Savoie Mont Blanc, CNRS, Laboratoire d’Annecy de Physique des Particules – IN2P3, 74000 Annecy, France
¹⁵ Universität Hamburg, Institut für Experimentalphysik, Luruper Chaussee 149, 22761 Hamburg, Germany
¹⁶ Graduate School of Science, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
¹⁷ Faculty of Science and Technology, Universidad del Azuay, Cuenca, Ecuador
¹⁸ Centro Brasileiro de Pesquisas Físicas, Rua Xavier Sigaud 150, 22290-180, Rio de Janeiro, Brazil
¹⁹ Instituto de Astrofísica de Canarias and Departamento de Astrofísica, Universidad de La Laguna, C. Vía Láctea, s/n, 38205 La Laguna, Santa Cruz de Tenerife, Spain
²⁰ CIEMAT, Avda. Complutense 40, 28040 Madrid, Spain
²¹ University of Geneva – Département de physique nucléaire et corpusculaire, 24 Quai Ernest Ansernet, 1211 Genève 4, Switzerland
²² INFN Sezione di Bari and Politecnico di Bari, via Orabona 4, 70124 Bari, Italy
²³ Institut de Fisica d’Altes Energies (IFAE), The Barcelona Institute of Science and Technology, Campus UAB, 08193 Bellaterra (Barcelona), Spain
²⁴ INAF – Osservatorio Astronomico di Brera, Via Brera 28, 20121 Milano, Italy
²⁵ Faculty of Physics and Applied Informatics, University of Lodz, ul. Pomorska 149-153, 90-236 Lodz, Poland
²⁶ INAF – Osservatorio di Astrofisica e Scienza dello spazio di Bologna, Via Piero Gobetti 93/3, 40129 Bologna, Italy
²⁷ INFN Sezione di Trieste and Università degli studi di Udine, via delle scienze 206, 33100 Udine, Italy
²⁸ INFN Sezione di Catania, Via S. Sofia 64, 95123 Catania, Italy
²⁹ INAF – Istituto di Astrofisica e Planetologia Spaziali (IAPS), Via del Fosso del Cavaliere 100, 00133 Roma, Italy
³⁰ Aix Marseille Univ, CNRS/IN2P3, CPPM, Marseille, France
³¹ University of Alcalá UAH, Departamento de Physics and Mathematics, Pza. San Diego, 28801 Alcalá de Henares, Madrid, Spain
³² INFN Sezione di Bari and Università di Bari, via Orabona 4, 70126 Bari, Italy
³³ INFN Sezione di Torino, Via P. Giuria 1, 10125 Torino, Italy
³⁴ Palacky University Olomouc, Faculty of Science, 17. listopadu 1192/12, 771 46 Olomouc, Czech Republic
³⁵ Dipartimento di Fisica e Chimica “E. Segrè”, Università degli Studi di Palermo, Via Archirafi 36, 90123 Palermo, Italy
³⁶ IRFU, CEA, Université Paris-Saclay, Bât 141, 91191 Gif-sur-Yvette, France
³⁷ Port d’Informació Científica, Edifici D, Carrer de l’Albareda, 08193 Bellaterrra (Cerdanyola del Vallès), Spain
³⁸ Department of Physics, TU Dortmund University, Otto-Hahn-Str. 4, 44227 Dortmund, Germany
³⁹ University of Rijeka, Department of Physics, Radmile Matejcic 2, 51000 Rijeka, Croatia
⁴⁰ Institute for Theoretical Physics and Astrophysics, Universität Würzburg, Campus Hubland Nord, Emil-Fischer-Str. 31, 97074 Würzburg, Germany
⁴¹ Department of Physics and Astronomy, University of Turku, FI- 20014 University of Turku, Finland
⁴² INFN Sezione di Roma La Sapienza, P.le Aldo Moro 2, 00185 Rome, Italy
⁴³ ILANCE, CNRS – University of Tokyo International Research Laboratory, University of Tokyo, 5-1-5 Kashiwa-no-Ha Kashiwa City, Chiba 277-8582, Japan
⁴⁴ Physics Program, Graduate School of Advanced Science and Engineering, Hiroshima University, 1-3-1 Kagamiyama, Higashi-Hiroshima City, Hiroshima 739-8526, Japan
⁴⁵ INFN Sezione di Roma Tor Vergata, Via della Ricerca Scientifica 1, 00133 Rome, Italy
⁴⁶ University of Split, FESB, R. Boškovića 32, 21000 Split, Croatia
⁴⁷ Department of Physics, Yamagata University, 1-4-12 Kojirakawamachi, Yamagata-shi 990-8560, Japan
⁴⁸ Institut für Theoretische Physik, Lehrstuhl IV: Plasma- Astroteilchenphysik, Ruhr-Universität Bochum, Universitätsstraße 150, 44801 Bochum, Germany
⁴⁹ Sendai College, National Institute of Technology, 4-16-1 Ayashi- Chuo, Aoba-ku, Sendai city, Miyagi 989-3128, Japan
⁵⁰ Josip Juraj Strossmayer University of Osijek, Department of Physics, Trg Ljudevita Gaja 6, 31000 Osijek, Croatia
⁵¹ INFN Dipartimento di Scienze Fisiche e Chimiche – Università degli Studi dell’Aquila and Gran Sasso Science Institute, Via Vetoio 1, Viale Crispi 7, 67100 L’Aquila, Italy
⁵² Chiba University, 1-33, Yayoicho, Inage-ku, Chiba-shi, Chiba 263-8522, Japan
⁵³ Kitashirakawa Oiwakecho, Sakyo Ward, Kyoto 606-8502, Japan
⁵⁴ FZU – Institute of Physics of the Czech Academy of Sciences, Na Slovance 1999/2, 182 21 Praha 8, Czech Republic
⁵⁵ Laboratory for High Energy Physics, École Polytechnique Fédérale, CH-1015 Lausanne, Switzerland
⁵⁶ Astronomical Institute of the Czech Academy of Sciences, Bocni II 1401, 14100 Prague, Czech Republic
⁵⁷ Faculty of Science, Ibaraki University, 2 Chome-1-1 Bunkyo, Mito, Ibaraki 310-0056, Japan
⁵⁸ Faculty of Science and Engineering, Waseda University, 3 Chome- 4-1 Okubo, Shinjuku City, Tokyo 169-0072, Japan
⁵⁹ Sorbonne Université, CNRS/IN2P3, Laboratoire de Physique Nucléaire et de Hautes Energies, LPNHE, 4 place Jussieu, 75005 Paris, France
⁶⁰ Institute of Particle and Nuclear Studies, KEK (High Energy Accelerator Research Organization), 1-1 Oho, Tsukuba, 305-0801, Japan
⁶¹ INFN Sezione di Trieste and Università degli Studi di Trieste, Via Valerio 2 I, 34127 Trieste, Italy
⁶² Escuela Politécnica Superior de Jaén, Universidad de Jaén, Campus Las Lagunillas s/n, Edif. A3, 23071 Jaén, Spain
⁶³ Saha Institute of Nuclear Physics, Sector 1, AF Block, Bidhan Nagar, Bidhannagar, Kolkata, West Bengal 700064, India
⁶⁴ Institute for Nuclear Research and Nuclear Energy, Bulgarian Academy of Sciences, 72 boul. Tsarigradsko chaussee, 1784 Sofia, Bulgaria
⁶⁵ Dipartimento di Fisica e Chimica ’E. Segrè’ Università degli Studi di Palermo, via delle Scienze, 90128 Palermo Italy
⁶⁶ Grupo de Electronica, Universidad Complutense de Madrid, Av. Complutense s/n, 28040 Madrid, Spain
⁶⁷ Institute of Space Sciences (ICE, CSIC), and Institut d’Estudis Espacials de Catalunya (IEEC), and Institució Catalana de Recerca I Estudis Avançats (ICREA), Campus UAB, Carrer de Can Magrans, s/n 08193 Bellatera, Spain
⁶⁸ Hiroshima Astrophysical Science Center, Hiroshima University 1-3-1 Kagamiyama, Higashi-Hiroshima, Hiroshima 739-8526, Japan
⁶⁹ School of Allied Health Sciences, Kitasato University, Sagamihara, Kanagawa 228-8555, Japan
⁷⁰ RIKEN, Institute of Physical and Chemical Research, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan
⁷¹ Charles University, Institute of Particle and Nuclear Physics, V Holešovičkách 2, 180 00 Prague 8, Czech Republic
⁷² Division of Physics and Astronomy, Graduate School of Science, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan
⁷³ Institute for Space-Earth Environmental Research, Nagoya University, Chikusa-ku, Nagoya 464-8601, Japan
⁷⁴ Kobayashi-Maskawa Institute (KMI) for the Origin of Particles and the Universe, Nagoya University, Chikusa-ku, Nagoya 464-8602, Japan
⁷⁵ Graduate School of Technology, Industrial and Social Sciences, Tokushima University, 2-1 Minamijosanjima, Tokushima 770-8506, Japan
⁷⁶ INFN Sezione di Pisa, Edificio C – Polo Fibonacci Largo Bruno Pontecorvo 3, 56127 Pisa Italy
⁷⁷ INFN Dipartimento di Scienze Fisiche e Chimiche – Università degli Studi dell’Aquila and Gran Sasso Science Institute, Via Vetoio 1, Viale Crispi 7, 67100 L’Aquila, Italy
⁷⁸ Gifu University, Faculty of Engineering, 1-1 Yanagido, Gifu 501-1193, Japan
⁷⁹ Department of Physical Sciences, Aoyama Gakuin University, Fuchinobe, Sagamihara, Kanagawa 252-5258, Japan
⁸⁰ Graduate School of Science and Engineering, Saitama University, 255 Simo-Ohkubo, Sakura-ku, Saitama city, Saitama 338-8570, Japan
⁸¹ Dipartimento di Fisica – Universitá degli Studi di Torino, Via Pietro Giuria 1, 10125 Torino, Italy
⁸² Department of Physics, Konan University, 8-9-1 Okamoto, Higashinada-ku Kobe 658-8501, Japan

^★ Corresponding author; gabriel.emery@cta-consortium.org

Received: 28 May 2024
Accepted: 27 September 2024

Abstract

Context. Imaging atmospheric Cherenkov telescopes (IACTs) are used to observe very high-energy photons from the ground. Gamma rays are indirectly detected through the Cherenkov light emitted by the air showers they induce. The new generation of experiments, in particular the Cherenkov Telescope Array Observatory (CTAO), sets ambitious goals for discoveries of new gamma-ray sources and precise measurements of the already discovered ones. To achieve these goals, both hardware and data analysis must employ cuttingedge techniques. This also applies to the LST-1, the first IACT built for the CTAO, which is currently taking data on the Canary island of La Palma.

Aims. This paper introduces a new event reconstruction technique for IACT data, aiming to improve the image reconstruction quality and the discrimination between the signal and the background from misidentified hadrons and electrons.

Methods. The technique models the development of the extensive air shower signal, recorded as a waveform per pixel, seen by CTAO telescopes’ cameras. Model parameters are subsequently passed to random forest regressors and classifiers to extract information on the primary particle.

Results. The new reconstruction was applied to simulated data and to data from observations of the Crab Nebula performed by the LST-1. The event reconstruction method presented here shows promising performance improvements. The angular and energy resolution, and the sensitivity, are improved by 10 to 20% over most of the energy range. At low energy, improvements reach up to 22%, 47%, and 50%, respectively. A future extension of the method to stereoscopic analysis for telescope arrays will be the next important step.