Pushing the VHE frontier: LST-1’s inaugural detection of the distant quasar OP 313

Result code in IS VaVaI

<a href="https://www.isvavai.cz/riv?ss=detail&h=RIV%2F67985815%3A_____%2F25%3A00646004" target="_blank" >RIV/67985815:_____/25:00646004 - isvavai.cz</a>

Alternative codes found

RIV/68378271:_____/25:00646004 RIV/61989592:15310/25:73635261

Result on the web

<a href="https://pos.sissa.it/501/569/pdf" target="_blank" >https://pos.sissa.it/501/569/pdf</a>

DOI - Digital Object Identifier

<a href="http://dx.doi.org/10.22323/1.501.0569" target="_blank" >10.22323/1.501.0569</a>

Result language

angličtina

Original language name

Pushing the VHE frontier: LST-1’s inaugural detection of the distant quasar OP 313

Original language description

In December 2023, the Flat Spectrum Radio Quasar OP 313 experienced an extraordinary very-high-energy (VHE, E > 100 GeV) gamma-ray flare, reaching an integral flux of 0.3 Crab Units above 100 GeV. This event marked the first VHE detection of OP 313 by the first Large-Sized Telescope~(LST-1) at the Northern site of the Cherenkov Telescope Array Observatory, delivering its inaugural scientific result and establishing OP 313 as the most distant blazar detected in this energy regime (z = 0.997). Coordinated observations with LST-1, the MAGIC telescopes, and extit{Fermi}-LAT enabled us to capture the detailed spectral and temporal evolution of the flare, which we compared with a low-emission state observed in January 2024. A complementary multi-wavelength campaign — from radio through X-rays — enabled us to construct and model the broad-band spectral energy distribution within a two-zone leptonic framework. In this scenario, synchrotron and external Compton processes, involving seed photons from the dusty torus and broad-line region, account for the observed emission, although several combinations of photon fields remain plausible. Furthermore, the broad energy coverage provided by our observations allowed us to probe the attenuation of VHE gamma-rays by the Extragalactic Background Light, yielding competitive upper limits on its intensity. This work not only demonstrates the breakthrough capabilities of LST-1 in VHE gamma-ray astronomy but also provides fresh insights into the complex radiative mechanisms of high-redshift blazars, paving the way for future studies of extreme extragalactic sources.

Czech name

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Czech description

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Type

D - Article in proceedings

CEP classification

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OECD FORD branch

10308 - Astronomy (including astrophysics,space science)

Project

Result was created during the realization of more than one project. More information in the Projects tab.

Continuities

I - Institucionalni podpora na dlouhodoby koncepcni rozvoj vyzkumne organizace

Publication year

2025

Confidentiality

S - Úplné a pravdivé údaje o projektu nepodléhají ochraně podle zvláštních právních předpisů

Article name in the collection

Proceedings of Science

ISBN

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ISSN

1824-8039

e-ISSN

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Number of pages

8

Pages from-to

569

Publisher name

Sissa Medilab srl

Place of publication

Trieste

Event location

Ženeva

Event date

Jul 15, 2025

Type of event by nationality

WRD - Celosvětová akce

UT code for WoS article

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