New Study by the LST-1 and MAGIC Collaborations Reveals Key Results from Observations of OP 313, the Most Distant Blazar Ever Detected at Very High Energies
A new study by the LST-1 and MAGIC collaborations presents important results from observations of gamma rays emitted by OP 313, the most distant blazar ever detected at very high energies. The analysis, published on August 11 in Astronomy & Astrophysics and involving researchers from the Italian National Institute for Nuclear Physics (INFN) and the National Institute for Astrophysics (INAF), combines observations from LST-1, the prototype Large-Sized Telescope for the future Cherenkov Telescope Array Observatory (CTAO), and the two MAGIC telescopes, located at the Roque de los Muchachos Observatory in La Palma, Spain.
The joint observations revealed a flux of very high-energy photons (gamma rays) originating from a distance of approximately eight billion light-years. By analyzing these data, researchers were able to obtain valuable information about the Extragalactic Background Light (EBL), the electromagnetic radiation emitted by all stars throughout the history of the Universe, and to gain further insight into the complex particle acceleration mechanisms occurring within active galactic nuclei.
OP 313 is a particular type of active galactic nucleus known as a blazar. At its core lies a supermassive black hole that generates a powerful jet of particles, gas, and radiation pointed toward Earth. More specifically, it is classified as a Flat Spectrum Radio Quasar (FSRQ), a particularly luminous class of blazars.
Approximately eight billion years ago, OP 313 produced the powerful flare of very high-energy gamma rays detected by the LST-1 and MAGIC telescopes. During their journey through the cosmos, these gamma rays were attenuated through interactions with the Extragalactic Background Light (EBL). When gamma rays collide with EBL photons, they produce particle pairs, particularly electron-positron pairs. As a result, observing such radiation is only possible with highly sensitive instruments. The analysis of this gamma-ray flux enabled the LST-1 and MAGIC collaborations to place stringent constraints on the density of the EBL.
“By analyzing the attenuation of the very high-energy radiation we observe, we can infer the properties of the EBL and test the various existing models. Observing increasingly distant active galactic nuclei not only expands our understanding of these extreme objects, but also allows us to better understand how the Universe and the light that fills it have evolved,” explains Jorge Otero Santos, INFN researcher, MAGIC Extragalactic Physics Coordinator, former LST-1 Extragalactic Physics Coordinator, and co-leader of this analysis. He adds: “The discovery of OP 313 demonstrates the enormous potential of LST-1 in view of the start of CTAO operations, while also confirming the effectiveness of the MAGIC telescopes, which have been at the forefront of high-energy astrophysics for the past 20 years.”
The study also shows that the intense gamma-ray emission is consistent with the presence of a dense population of relativistic electrons near the source, according to the so-called leptonic scenario. In this framework, the massive plasma jet emitted by OP 313’s supermassive black hole accelerates electrons to velocities close to the speed of light. These relativistic electrons then interact with the low-energy photons surrounding the black hole, transferring part of their energy and boosting them into very high-energy gamma rays.
The high-energy astrophysics group at INFN Padova and Padova University has played a crucial role in the discovery of OP 313 and the interpretation of the observations. Jorge Otero Santos, currently an INFN postdoctoral fellow in the group, has co-led this study and has led the analysis of the LST data and theoretical interpretation of the emission of this distant quasar. This work represents a step forward in our understanding of this still under-represented blazar type and in our knowledge of the EBL and the evolution of the Universe.
Italian participation in the CTAO LST and MAGIC collaborations involves INFN, INAF, and researchers from the Universities of Bari, Bologna, L’Aquila, Naples, Palermo, Padua, Pisa, Siena, Udine, Turin, and Trieste, as well as the Polytechnic University of Bari and the Gran Sasso Science Institute.
Read the article: https://doi.org/10.1051/0004-6361/202558646
The Telescopes
LST-1 is the prototype of the Large-Sized Telescopes currently undergoing testing at the northern CTAO site in La Palma, Spain. The LSTs are designed to observe the lowest-energy component of the gamma-ray radiation that will be studied by the Cherenkov Telescope Array Observatory (CTAO). The CTAO LST Collaboration brings together more than 500 scientists and engineers from 25 institutions across 11 countries. Italy plays a leading role in the collaboration, with researchers from INFN, INAF, and numerous Italian universities contributing to telescope development and construction, testing activities, and scientific data analysis.
The MAGIC (Major Atmospheric Gamma Imaging Cherenkov) telescopes are two Cherenkov telescopes operating together from the same site in La Palma. The first telescope began operations in 2003, while the second became operational in 2009. The MAGIC Collaboration comprises nearly 400 scientists and engineers from 12 countries, including Italy, which has participated in the project since its inception. Italian researchers have contributed to instrument development, data collection and analysis, and the study of very high-energy astrophysical phenomena.
Image credit: Mireia Nievas Rosillo.
