MAGIC observations provide compelling evidence of hadronic multi-TeV emission from the putative PeVatron SNR G106.3+2.7

¹ Japanese MAGIC Group: Institute for Cosmic Ray Research (ICRR), The University of Tokyo, Kashiwa, 277-8582 Chiba, Japan
² Instituto de Astrofisica de Canarias and Dpto. de Astrofisica, Universidad de La Laguna, 38200 La Laguna, Tenerife, Spain
³ Instituto de Astrofisica de Andalucia-CSIC, Glorieta de la Astronomia s/n, 18008 Granada, Spain
⁴ National Institute for Astrophysics (INAF), 00136 Rome, Italy
⁵ Università di Udine and INFN Trieste, 33100 Udine, Italy
⁶ Max-Planck-Institut für Physik, 80805 München, Germany
⁷ Università di Padova and INFN, 35131 Padova, Italy
⁸ Institut de Fisica d'Altes Energies (IFAE), The Barcelona Institute of Science and Technology (BIST), 08193 Bellaterra (Barcelona), Spain
⁹ Technische Universität Dortmund, 44221 Dortmund, Germany
¹⁰ Croatian MAGIC Group: University of Zagreb, Faculty of Electrical Engineering and Computing (FER), 10000 Zagreb, Croatia
¹¹ IPARCOS Institute and EMFTEL Department, Universidad Complutense de Madrid, 28040 Madrid, Spain
¹² Centro Brasileiro de Pesquisas Físicas (CBPF), 22290-180 URCA, Rio de Janeiro (RJ), Brazil
¹³ University of Lodz, Faculty of Physics and Applied Informatics, Department of Astrophysics, 90-236 Lodz, Poland
¹⁴ Deutsches Elektronen-Synchrotron (DESY), 15738 Zeuthen, Germany
¹⁵ ETH Zürich, 8093 Zürich, Switzerland
¹⁶ Università di Pisa and INFN Pisa, 56126 Pisa, Italy
¹⁷ Universitat de Barcelona, ICCUB, IEEC-UB, 08028 Barcelona, Spain
¹⁸ Armenian MAGIC Group: A. Alikhanyan National Science Laboratory, 0036 Yerevan, Armenia
¹⁹ Centro de Investigaciones Energéticas, Medioambientales y Tecnologicas, 28040 Madrid, Spain
²⁰ Department for Physics and Technology, University of Bergen, 5007 Bergen, Norway
²¹ INFN MAGIC Group: INFN Sezione di Catania and Dipartimento di Fisica e Astronomia, University of Catania, 95123 Catania, Italy
²² INFN MAGIC Group: INFN Sezione di Torino and Università degli Studi di Torino, 10125 Torino, Italy
²³ INFN MAGIC Group: INFN Sezione di Bari and Dipartimento Interateneo di Fisica dell'Università e del Politecnico di Bari, 70125 Bari, Italy
²⁴ Croatian MAGIC Group: University of Rijeka, Faculty of Physics, 51000 Rijeka, Croatia
²⁵ Universität Würzburg, 97074 Würzburg, Germany
²⁶ University of Geneva, Chemin d'Ecogia 16, 1290 Versoix, Switzerland
²⁷ Finnish MAGIC Group: Finnish Centre for Astronomy with ESO, University of Turku, 20014 Turku, Finland
²⁸ Departament de Fisica, and CERES-IEEC, Universitat Autönoma de Barcelona, 08193 Bellaterra, Spain
²⁹ Japanese MAGIC Group: Physics Program, Graduate School of Advanced Science and Engineering, Hiroshima University, 739-8526 Hiroshima, Japan
³⁰ Armenian MAGIC Group: ICRANet-Armenia, 0019 Yerevan, Armenia
³¹ Croatian MAGIC Group: University of Split, Faculty of Electrical Engineering, Mechanical Engineering and Naval Architecture (FESB), 21000 Split, Croatia
³² Croatian MAGIC Group: Josip Juraj Strossmayer University of Osijek, Department of Physics, 31000 Osijek, Croatia
³³ Japanese MAGIC Group: Department of Physics, Tokai University, Hiratsuka, 259-1292 Kanagawa, Japan
³⁴ Università di Siena and INFN Pisa, 53100 Siena, Italy
³⁵ Saha Institute of Nuclear Physics, A CI of Homi Bhabha National Institute, Kolkata 700064, West Bengal, India
³⁶ Inst. for Nucl. Research and Nucl. Energy, Bulgarian Academy of Sciences, 1784 Sofia, Bulgaria
³⁷ Japanese MAGIC Group: Department of Physics, Yamagata University, Yamagata 990-8560, Japan
³⁸ Finnish MAGIC Group: Space Physics and Astronomy Research Unit, University of Oulu, 90014 Oulu, Finland
³⁹ Japanese MAGIC Group: Department of Physics, Kyoto University, 606-8502 Kyoto, Japan
⁴⁰ Japanese MAGIC Group: Institute for Space-Earth Environmental Research and Kobayashi-Maskawa Institute for the Origin of Particles and the Universe, Nagoya University, 464-6801 Nagoya, Japan
⁴¹ Croatian MAGIC Group: Ruđer Bošković Institute, 10000 Zagreb, Croatia
⁴² INFN MAGIC Group: INFN Sezione di Perugia, 06123 Perugia, Italy
⁴³ INFN MAGIC Group: INFN Roma Tor Vergata, 00133 Roma, Italy
⁴⁴ Japanese MAGIC Group: Department of Physics, Konan University, Kobe, Hyogo 658-8501, Japan
⁴⁵ International Center for Relativistic Astrophysics (ICRA), Rome, Italy
⁴⁶ Port d'Informacio Cientifica (PIC), 08193 Bellaterra (Barcelona), Spain
⁴⁷ Ruhr-Universität Bochum, Fakultät für Physik und Astronomie, Astronomisches Institut (AIRUB), 44801 Bochum, Germany
⁴⁸ University of Innsbruck, Institute for Astro- and Particle Physics, University of Innsbruck, A-6020 Innsbruck, Austria
⁴⁹ Dipartimento di Fisica, Università di Trieste, 34127 Trieste, Italy
⁵⁰ University of Lodz, Faculty of Physics and Applied Informatics, Department of Astrophysics, 90-236 Lodz, Poland

Received: 9 September 2022
Accepted: 11 November 2022

Abstract

Context. Certain types of supernova remnants (SNRs) in our Galaxy are assumed to be PeVatrons, capable of accelerating cosmic rays (CRs) to ~ PeV energies. However, conclusive observational evidence for this has not yet been found. The SNR G106.3+2.7, detected at 1–100 TeV energies by different γ-ray facilities, is one of the most promising PeVatron candidates. This SNR has a cometary shape, which can be divided into a head and a tail region with different physical conditions. However, in which region the 100 TeV emission is produced has not yet been identified because of the limited position accuracy and/or angular resolution of existing observational data. Additionally, it remains unclear as to whether the origin of the γ-ray emission is leptonic or hadronic.

Aims. With the better angular resolution provided by new MAGIC data compared to earlier γ-ray datasets, we aim to reveal the acceleration site of PeV particles and the emission mechanism by resolving the SNR G106.3+2.7 with 0.1° resolution at TeV energies.

Methods. We observed the SNR G106.3+2.7 using the MAGIC telescopes for 121.7 h in total – after quality cuts – between May 2017 and August 2019. The analysis energy threshold is ~0.2 TeV, and the angular resolution is 0.07−0.1°. We examined the γ-ray spectra of different parts of the emission, whilst benefitting from the unprecedented statistics and angular resolution at these energies provided by our new data. We also used measurements at other wavelengths such as radio, X-rays, GeV γ-rays, and 10 TeV γ-rays to model the emission mechanism precisely.

Results. We detect extended γ-ray emission spatially coincident with the radio continuum emission at the head and tail of SNR G106.3+2.7. The fact that we detect a significant γ-ray emission with energies above 6.0 TeV from only the tail region suggests that the emissions above 10 TeV detected with air shower experiments (Milagro, HAWC, Tibet ASγ and LHAASO) are emitted only from the SNR tail. Under this assumption, the multi-wavelength spectrum of the head region can be explained with either hadronic or leptonic models, while the leptonic model for the tail region is in contradiction with the emission above 10 TeV and X-rays. In contrast, the hadronic model could reproduce the observed spectrum at the tail by assuming a proton spectrum with a cutoff energy of ~1 PeV for that region. Such high-energy emission in this middle-aged SNR (4−10 kyr) can be explained by considering a scenario where protons escaping from the SNR in the past interact with surrounding dense gases at present.

Conclusions. The γ-ray emission region detected with the MAGIC telescopes in the SNR G106.3+2.7 is extended and spatially coincident with the radio continuum morphology. The multi-wavelength spectrum of the emission from the tail region suggests proton acceleration up to ~PeV, while the emission mechanism of the head region could either be hadronic or leptonic.