First detection of the Crab Nebula at TeV energies with a Cherenkov telescope in a dual-mirror Schwarzschild-Couder configuration: the ASTRI-Horn telescope

¹ INAF Osservatorio Astronomico di Roma, 00078 Monte Porzio Catone, Roma, Italy
² ASI Space Science Data Center, 00133 Roma, Italy
³ INAF IASF Palermo, 90146 Palermo, Italy
⁴ INAF IASF Milano, 20133 Milano, Italy
⁵ INAF Osservatorio Astronomico di Brera, 23807 Merate, LC, Italy
⁶ CTA Observatory, 40129 Bologna, Italy
⁷ LUPM IN2P3, Université de Montpellier, 34095 Montpellier, France
⁸ INAF Osservatorio Astronomico di Catania, 95123 Catania, Italy
⁹ MPI für Kernphysik, 69117 Heidelberg, Germany
¹⁰ CSR, North-West University, 2520 Potchefstroom, South Africa
¹¹ LPSC IN2P3, Université de Grenoble-Alpes, 38400 Saint-Martin-d’Hères, France
¹² INAF OAS Bologna, 40129 Bologna, Italy
¹³ IAG USP, Universidade de São Paulo, 5508-090 São Paulo, SP, Brazil
¹⁴ INAF Osservatorio Astronomico di Padova, 35122 Padova, Italy
¹⁵ INAF IRA Noto Station, 96017 Noto, SR, Italy
¹⁶ INAF IAPS Roma, 00133 Roma, Italy
¹⁷ Dipartimento di Fisica e Geologia, Università di Perugia, 06123 Perugia, Italy
¹⁸ INAF Osservatorio Astronomico di Capodimonte, 80131 Napoli, Italy

Received: 26 September 2019
Accepted: 20 December 2019

Abstract

We report on the first detection of very high-energy gamma-ray emission from the Crab Nebula by a Cherenkov telescope in dual-mirror Schwarzschild-Couder (SC) configuration. This result has been achieved by means of the 4 m ASTRI-Horn telescope, operated on Mt. Etna, Italy, and developed in the context of the Cherenkov Telescope Array Observatory preparatory phase. The dual-mirror SC design is aplanatic and characterized by a small plate scale, which allows us to implement large cameras with a large field of view, with small-size pixel sensors and a high level of compactness. The curved focal plane of the ASTRI camera is covered by silicon photo-multipliers, managed by an unconventional front-end electronic system that is based on a customized peak-sensing detector mode. The system includes internal and external calibration systems, hardware and software for control and acquisition, and the complete data archiving and processing chain. These observations of the Crab Nebula were carried out in December 2018 during the telescope verification phase for a total observation time (after data selection) of 24.4 h, equally divided between on- and off-axis source exposure. The camera system was still under commission and its functionality was not yet completely exploited. Furthermore, due to recent eruptions of the Etna Volcano, the mirror reflection efficiency was reduced. Nevertheless, the observations led to the detection of the source with a statistical significance of 5.4σ above an energy threshold of ∼3 TeV. This result provides an important step toward the use of dual-mirror systems in Cherenkov gamma-ray astronomy. A pathfinder mini-array based on nine ASTRI-like telescopes with a large field-of-view is in the course of implementation.