First detection of VHE gamma-ray signal from the FSRQ TON 0599

Abe, K; Abe, S; Abhir, J; Abhishek, A; Acciari, VA; Aguasca-Cabot, A; Agudo, I; Aniello, T; Ansoldi, S; Antonelli, LA; Engels, AA; Arcaro, C; Asano, K; Babić, A; De Almeida, UB; Barrio, JA; Barrios-Jiménez, L; Batković, I; Baxter, J; González, JB; Bednarek, W; Bernardini, E; Bernete, J; Berti, A; Besenrieder, J; Bigongiari, C; Biland, A; Blanch, O; Bonnoli, G; Bošnjak; Bronzini, E; Burelli, I; Campoy-Ordaz, A; Carosi, A; Carosi, R; Carretero-Castrillo, M; Castro-Tirado, AJ; Cerasole, D; Ceribella, G; Chai, Y; Cifuentes, A; Contreras, JL; Cortina, J; Covino, S; D'Amico, G; Da Vela, P; Dazzi, F; De Angelis, A; De Lotto, B; De Menezes, R; Delfino, M; Delgado, J; Mendez, CD; Pierro, FD; Tria, RD; Venere, LD; Dinesh, A; Prester, DD; Donini, A; Dorner, D; Doro, M; Eisenberger, L; Elsaesser, D; Escudero, J; Foffano, L; Font, L; Fröse, S; Fukami, S; Fukazawa, Y; Garczarczyk, M; Gasparyan, S; Gaug, M; Paiva, JGG; Giglietto, N; Giordano, F; Gliwny, P; Godinović, N; Gradetzke, T; Grau, R; Green, D; Green, JG; Günther, P; Hadasch, D; Hahn, A; Hassan, T; Heckmann, L; Llorente, JH; Hrupec, D; Imazawa, R; Israyelyan, D; Martínez, IJ; Quiles, JJ; Jormanainen, J; Kankkunen, S; Kerszberg, D; Khachatryan, M; Konrad, J; Kouch, PM; Kubo, H; Kushida, J; Láinez, M; Lamastra, A; Lindfors, E; Lombardi, S; Longo, F; López-Coto, R; López-Moya, M; López-Oramas, A; Loporchio, S; Lorini, A; Lulić, A; Lyard, E; Majumdar, P; Makariev, M; Maneva, G; Manganaro, M; Mangano, S; Mannheim, K; Mariotti, M; Jermak, HE; Steele, IE

First detection of VHE gamma-ray signal from the FSRQ TON 0599

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Abe, K, Abe, S, Abhir, J, Abhishek, A, Acciari, VA, Aguasca-Cabot, A ORCID: 0000-0001-8816-4920, Agudo, I, Aniello, T, Ansoldi, S, Antonelli, LA, Engels, AA, Arcaro, C, Asano, K, Babić, A, De Almeida, UB, Barrio, JA, Barrios-Jiménez, L, Batković, I, Baxter, J, González, JB et al (2026) First detection of VHE gamma-ray signal from the FSRQ TON 0599. Monthly Notices of the Royal Astronomical Society, 546 (4). ISSN 0035-8711

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Publisher URL: https://doi.org/10.1093/mnras/stag032

Open Access URL: https://doi.org/10.1093/mnras/stag032 (Published version)

Abstract

TON 0599 (z = 0.7247) belongs to the few flat spectrum radio quasars (FSRQs) detected in the very high energy (VHE, 100GeV) gamma-ray band. Its redshift makes it currently one of the farthest VHE gamma-ray sources. It was detected for the first time with the MAGIC telescopes on 2017 December 15, and observed until December 29. The flux reached a maximum of about 50 per cent of the Crab Nebula flux above 80 GeV on the second night of observation, after which we witnessed a gradual decrease of the flux. The VHE gamma-ray spectrum connects smoothly to the one in the high energy (100 MeV) band obtained from simultaneous observations with Fermi-LAT. It features a cut-off at energies around 50 GeV, indicating the location of the gamma-ray emission zone beyond the broad line region. In addition, we were able to follow the spectral evolution during the fading phase of the flare. Multiwavelength analysis based on observations in optical, near-infrared, and radio bands acquired by the Whole Earth Blazar Telescope Collaboration from November to March, as well as observations in X-ray and optical-UV bands with instruments on board the Swift satellite, shows strong correlation between different bands. We model the broadband emission with a simple one-zone leptonic model, where the high-energy peak is predominantly produced by external Compton scattering of photons from the dusty torus.

Item Type:	Article
Uncontrolled Keywords:	alaxies: active; quasars: individual: TON 0599; galaxies: jets; gamma-rays: galaxies; astro-ph.HE; astro-ph.HE; 5106 Nuclear and Plasma Physics; 5101 Astronomical Sciences; 51 Physical Sciences; 5106 Nuclear and Plasma Physics; 5101 Astronomical Sciences; 51 Physical Sciences; 0201 Astronomical and Space Sciences; Astronomy & Astrophysics; 5101 Astronomical sciences; 5107 Particle and high energy physics; 5109 Space sciences
Subjects:	Q Science > QB Astronomy
Divisions:	Astrophysics Research Institute
Publisher:	Oxford University Press
Date of acceptance:	24 December 2025
Date of first compliant Open Access:	11 June 2026
Date Deposited:	11 Jun 2026 13:28
Last Modified:	11 Jun 2026 13:28
DOI or ID number:	10.1093/mnras/stag032
URI:	https://researchonline.ljmu.ac.uk/id/eprint/28816

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