The CTAO LST-1 (left) and the MAGIC telescopes (right) observing together on the Canary Island of La Palma.
Photo Credit: © Mireia Nievas Rosillo
Scientific Frontline: Extended "At a Glance" Summary: Blazar OP 313
The Core Concept: Blazar OP 313 is an exceptionally bright active galactic nucleus, specifically classified as a flat-spectrum radio quasar, powered by a central supermassive black hole.
Key Distinction/Mechanism: It emits a powerful burst of very high-energy photons (gamma rays) through a process where electrons are accelerated to near-light speeds and collide with lower-energy photons, propelling them to higher energy levels (leptonic scenario).
Origin/History: The high-energy gamma ray burst from OP 313, located about eight billion light-years away, was discovered in December 2023. It dates back to a period after the Universe's peak activity, known as the "Cosmic noon," began to slow down.
Major Frameworks/Components:
- Flat-spectrum radio quasar
- Extragalactic background light (EBL)
- Pair production (conversion of gamma ray energy into an electron and a positron)
- Leptonic scenario of particle acceleration
Branch of Science: Astronomy, Astrophysics, Nuclear and Particle Physics.
Future Application: Further research will continue using the completed Large-Sized Telescopes (LST) array to expand the gamma-ray horizon and deepen understanding of extragalactic backgrounds and particle acceleration mechanisms.
Why It Matters: This is the most distant very high-energy blazar ever detected, providing crucial data on the extragalactic background light density and the internal mechanisms of flat-spectrum radio quasars.
An international team, including researchers from UNIGE, has announced the discovery of the most distant blazar ever detected.
Blazars are exceptionally bright active galactic nuclei, powered by a central supermassive black hole. Thanks to the Cherenkov Telescope Array Observatory (CTAO), for which the University of Geneva (UNIGE) leads the Swiss consortium, scientists have announced that they have observed a very high-energy blazar at a distance of around eight billion light-years—the most distant ever recorded. These findings have been published in the journal Astronomy & Astrophysics.
Blazar OP 313 is classified as a flat-spectrum radio quasar, a particular type of blazar that ranks among the brightest and most powerful sources of radiation in the universe. "Around 11 billion years ago, the universe experienced a period of peak activity known as 'cosmic noon,' characterized by an intense rate of star and galaxy formation," explains Axel Arbet-Engels, a research fellow in the Department of Astronomy at UNIGE and among the corresponding authors of the study. "When this phase of intense activity slowed down and galaxies began to evolve and mature, the universe entered a calmer phase, which continues to this day."
It was at the start of this period that OP 313 emitted the powerful burst of very high-energy photons (gamma rays) discovered in December 2023 and brought to the attention of the astronomical community. Further observations of the blazar OP 313 were then carried out using the Large-Sized Telescope (LST-1) prototype and the Major Atmospheric Gamma-ray Imaging Cherenkov (MAGIC) telescope, both located at the Roque de los Muchachos Observatory on La Palma, Spain.
These joint observations detected a flux of high-energy gamma rays originating from a distance of approximately eight billion light-years. By analyzing these gamma rays, the scientists were able to gather essential information about the extragalactic background (EBL) and unravel the complex particle acceleration processes at work within the "engine" of this distant galaxy.
This discovery is proof of the telescope's exceptional performance and its promising future.
While these extremely high-energy gamma rays traveled through the cosmos for eight billion years, they interacted with the EBL, an omnipresent field of radiation spanning all energy scales, produced by cosmic objects throughout the history of the universe. This interaction attenuates the gamma-ray signal through a process known as "pair production." When these gamma rays collide with the EBL, their energy is converted into pairs of particles—specifically, an electron and a positron. Consequently, the initial flux of gamma rays from the cosmic source diminishes as it travels this immense distance, making its detection particularly difficult. To achieve this, instruments with exceptional sensitivity are required.
By analyzing combined data from the LST-1 and MAGIC telescopes, as well as lower-energy data from other facilities, the authors of the paper obtained precise information on the density of the EBL and characterized the variability of the flux. The team determined that the intense gamma-ray emission was fueled by a dense population of so-called "relativistic" electrons.
"In what is known as the leptonic scenario, electrons have been accelerated to speeds close to the speed of light within a powerful plasma jet ejected by the central supermassive black hole of OP 313," explains Domenico Della Volpe, a professor in the Department of Nuclear and Particle Physics at UNIGE, coauthor of the paper, and representative of the Swiss consortium in the CTAO Council. "Upon colliding with lower-energy photons surrounding the black hole, the electrons transfer part of their considerable energy to these photons, thereby propelling them to energy levels corresponding to very high-energy gamma rays." These results represent a major breakthrough in understanding the internal mechanisms of flat-spectrum radio quasars.
The LST array, soon to be inaugurated
The LST-1 is the prototype of the Large-Sized Telescopes (LST), currently undergoing commissioning at the CTAO-North site on La Palma, Spain. The discovery of the most distant very high-energy blazar ever observed during this testing phase is proof of the telescope's exceptional performance and its promising future in expanding the gamma-ray horizon at very high energies. On October 15, 2026, the complete LST subarray, comprising three additional telescopes, will be inaugurated on La Palma by the LST collaboration. Designed to extend the CTAO's sensitivity at low energies down to 20 GeV, future observations by the LSTs will significantly broaden the gamma-ray horizon, thereby offering scientists the opportunity to observe extreme radiation at distances never before reached.
Additional information: The CTAO LST collaboration is an in-kind contributor (IKC) to the CTAO and is responsible for the construction of the Large-Sized Telescopes (LST). It brings together more than 500 scientists and engineers from 25 institutions across 11 countries: Brazil, Bulgaria, Croatia, the Czech Republic, France, Germany, Italy, Japan, Poland, Spain, and Switzerland.
Published in journal: Astronomy & Astrophysics
Title: Detection of the distant quasar OP 313 with the first Large-Sized Telescope of CTAO
Authors: K. Abe, S. Abe, J. Abhir, A. Abhishek, V. A. Acciari, F. Acero, A. Aguasca-Cabot, I. Agudo, C. Alispach, D. Ambrosino, T. Aniello, S. Ansoldi, L. A. Antonelli, C. Aramo, A. Arbet-Engels, C. Arcaro, T. T. H. Arnesen, K. Asano, P. Aubert, A. Babić, C. Bakshi, A. Baktash, M. Balbo, A. Bamba, A. Baquero Larriva, V. Barbosa Martins, U. Barres de Almeida, J. A. Barrio, L. Barrios Jiménez, I. Batkovic, J. Baxter, J. Becerra González, W. Bednarek, E. Bernardini, J. Bernete, A. Berti, J. Besenrieder, C. Bigongiari, A. Biland, E. Bissaldi, O. Blanch, Ž. Bošnjak, G. Bonnoli, P. Bordas, G. Borkowski, A. Briscioli, E. Bronzini, G. Brunelli, J. Buces, A. Bulgarelli, I. Burelli, L. Burmistrov, A. Campoy-Ordaz, M. Cardillo, S. Caroff, A. Carosi, R. Carosi, R. Carraro, M. S. Carrasco, M. Carretero-Castrillo, F. Cassol, A. J. Castro-Tirado, D. Cerasole, G. Ceribella, A. Cerviño Cortínez, Y. Chai, K. Cheng, A. Chiavassa, M. Chikawa, G. Chon, L. Chytka, G. M. Cicciari, A. Cifuentes Santos, J. L. Contreras, J. Cortina, H. Costantini, S. Covino, M. Croisonnier, G. D’Amico, P. Da Vela, M. Dalchenko, F. Dazzi, A. De Angelis, M. de Bony de Lavergne, B. De Lotto, R. de Menezes, G. De Palma, V. de Souza, R. Del Burgo, L. Del Peral, M. Delfino, C. Delgado Mendez, J. Delgado Mengual, D. della Volpe, A. Di Piano, F. Di Pierro, R. Di Tria, L. Di Venere, C. Díaz, A. Dinesh, D. Dominis Prester, A. Donini, D. Dorner, M. Doro, L. Eisenberger, D. Elsässer, G. Emery, J. Escudero, L. Fariña, L. Feligioni, F. Ferrarotto, A. Fiasson, L. Foffano, L. Font, F. Frías García-Lago, S. Fröse, Y. Fukazawa, S. Gallozzi, R. J. García López, S. Garcia Soto, C. Gasbarra, D. Gasparrini, S. Gasparyan, M. Gaug, J. G. Giesbrecht Paiva, N. Giglietto, F. Giordano, P. Gliwny, N. Godinovic, T. Gradetzke, R. Grau, L. Greaux, D. Green, J. Green, G. Grolleron, S. Gunji, P. Günther, J. Hackfeld, D. Hadasch, A. Hahn, G. Harutyunyan, M. Hashizume, T. Hassan, K. Hayashi, L. Heckmann, M. Heller, J. Herrera Llorente, K. Hirotani, D. Hoffmann, D. Horns, J. Houles, M. Hrabovsky, D. Hrupec, D. Hui, M. Iarlori, R. Imazawa, T. Inada, Y. Inome, S. Inoue, K. Ioka, M. Iori, D. Israyelyan, T. Itokawa, A. Iuliano, J. Jahanvi, I. Jimenez Martinez, J. Jimenez Quiles, I. Jorge Rodrigo, J. Jormanainen, J. Jurysek, M. Kagaya, O. Kalashev, S. Kankkunen, V. Karas, H. Katagiri, T. Kayanoki, D. Kerszberg, M. Kherlakian, T. Kiyomot, G. W. Kluge, Y. Kobayashi, K. Kohri, A. Kong, J. Konrad, P. Kornecki, P. M. Kouch, G. Koziol, H. Kubo, J. Kushida, B. Lacave, M. Lainez, G. Lamanna, A. Lamastra, L. Lemoigne, E. Lindfors, M. Linhoff, S. Lombardi, F. Longo, R. López-Coto, M. López-Moya, A. López-Oramas, S. Loporchio, A. Lorini, J. Lozano Bahilo, F. Lucarelli, H. Luciani, L. Lulić, P. L. Luque-Escamilla, E. Lyard, P. Majumdar, M. Makariev, M. Mallamaci, D. Mandat, G. Maneva, M. Manganaro, S. Mangano, D. K. Maniadakis, G. Manicò, K. Mannheim, S. Marchesi, F. Marini, M. Mariotti, P. Marquez, G. Marsella, M. Martínez, J. Martí, G. Martínez, M. Martínez, O. Martinez, P. Maruševec, A. Mas-Aguilar, M. Massa, G. Maurin, D. Mazin, J. Méndez-Gallego, S. Menon, E. Mestre Guillen, D. Miceli, T. Miener, J. M. Miranda, R. Mirzoyan, M. Mizote, T. Mizuno, M. Molero Gonzalez, E. Molina, H. A. Mondal, T. Montaruli, A. Moralejo, D. Morcuende, A. Moreno Ramos, A. Morselli, V. Moya, A. L. Müller, H. Muraishi, S. Nagataki, T. Nakamori, C. Nanci, A. Negro, A. Neronov, V. Neustroev, D. Nieto Castaño, M. Nievas Rosillo, C. Nigro, L. Nikolic, K. Nilsson, K. Nishijima, K. Noda, D. Nosek, V. Novotny, S. Nozaki, M. Ohishi, Y. Ohtani, T. Oka, A. Okumura, R. Orito, L. Orsini, J. Otero-Santos, P. Ottanelli, S. Paiano, M. Palatiello, G. Panebianco, D. Paneque, F. R. Pantaleo, R. Paoletti, J. M. Paredes, M. Pech, M. Pecimotika, M. Peresano, M. Persic, F. Pfeifle, E. Pietropaolo, M. Pihet, G. Pirola, C. Plard, F. Podobnik, M. Polo, P. G. Prada Moroni, E. Prandini, M. Prouza, S. Rainò, R. Rando, W. Rhode, M. Ribó, J. Rico, V. Rizi, G. Rodriguez Fernandez, M. D. Rodríguez Frías, P. Romano, A. Roy, A. Ruina, E. Ruiz-Velasco, N. Sahakyan, T. Saito, S. Sakurai, D. A. Sanchez, H. Sano, E. Santos Moura, T. Šarić, Y. Sato, F. G. Saturni, V. Savchenko, F. Schiavone, B. Schleicher, K. Schmitz, F. Schmuckermaier, F. Schussler, T. Schweizer, A. Sciaccaluga, M. Seglar Arroyo, T. Siegert, G. Silvestri, A. Simongini, J. Sitarek, V. Sliusar, D. Sobczynska, I. Sofia, A. Stamerra, J. Strišković, D. Strom, M. Strzys, Y. Suda, A. Sunny, H. Tajima, M. Takahashi, J. Takata, R. Takeishi, P. H. T. Tam, S. J. Tanaka, D. Tateishi, T. Tavernier, P. Temnikov, Y. Terada, K. Terauchi, T. Terzic, M. Teshima, M. Tluczykont, F. Tokanai, T. Tomura, D. F. Torres, F. Tramonti, P. Travnicek, G. Tripodo, A. Tutone, S. Ubach, M. Vacula, J. van Scherpenberg, M. Vázquez Acosta, S. Ventura, S. Vercellone, G. Verna, I. Viale, A. Viana, A. Vigliano, C. F. Vigorito, E. Visentin, V. Vitale, V. Voitsekhovskyi, G. Voutsinas, I. Vovk, T. Vuillaume, R. Walter, C. Walther, L. Wan, F. Wersig, M. Will, J. Wójtowicz, T. Yamamoto, R. Yamazaki, Y. Yao, P. K. H. Yeung, T. Yoshida, T. Yoshikoshi, W. Zhang, I. Myserlis, R. Rao, M. Gurwell, G. Keating, A. Marscher, S. Jorstad, E. Angelakis, A. Kraus, C. Thum, J. A. Acosta-Pulido, A. Marchini, L. Stiaccini, P. Aceti, M. Banfi, S. Leonini, M. Conti, P. Rosi, L. M. Tinjaca Ramirez, J. Escudero Pedrosa, A. Sota, V. Casanova, F. J. Aceituno, and V. Fallah Ramazani
Source/Credit: Université de Genève
Edited by: Scientific Frontline
Reference Number: astr100626_01
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