Letter to the Editor

Magnetically driven relativistic jet in the high-redshift blazar OH 471

¹ Shanghai Astronomical Observatory, Chinese Academy of Sciences (CAS), 80 Nandan Road, Shanghai, 200030, PR China
e-mail: sgguo@shao.ac.cn; antao@shao.ac.cn
² School of Astronomy and Space Sciences, University of Chinese Academy of Sciences, No. 19A Yuquan Road, Beijing, 100049, PR China
³ Key Laboratory of Radio Astronomy and Technology, CAS, A20 Datun Road, Beijing, 100101, PR China
⁴ Special Astrophysical Observatory of RAS, Nizhny Arkhyz, 369167, Russia
⁵ Radio Astronomy and Geodynamics Department, Crimean Astrophysical Observatory, Katsiveli, 22, Crimea
⁶ Kazan Federal University, 18 Kremlyovskaya St, Kazan, 420008, Russia
⁷ Xinjiang Astronomical Observatory, Chinese Academy of Sciences, 150 Science 1-Street, Urumqi, Xinjiang, 830011, PR China
⁸ Lebedev Physical Institute (Astro Space Center), Leninsky prospect 53, Moscow, 117997, Russia
⁹ Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, Bonn, 53121, Germany
¹⁰ Institute of Applied Astronomy, Russian Academy of Sciences, Kutuzova Embankment 10, St. Petersburg, 191187, Russia
¹¹ Institute for Nuclear Research of the Russian Academy of Sciences, Moscow, 117312, Russia

Received: 11 March 2024
Accepted: 24 April 2024

Abstract

Context. Understanding the mechanisms that launch and shape powerful relativistic jets from supermassive black holes (SMBHs) in high-redshift active galactic nuclei (AGNs) is crucial for probing the co-evolution of SMBHs and galaxies over cosmic time.

Aims. We focus on the high-redshift (z = 3.396) blazar OH 471 to explore the jet launching mechanism in the early Universe.

Methods. Using multi-frequency radio monitoring observations and high-resolution Very Long Baseline Interferometry (VLBI) imaging over three decades, we studied the milliarcsecond structure and long-term variability of OH 471.

Results. Our spectral modeling of the radio flux densities revealed a synchrotron self-absorbed spectrum, indicating strong magnetic fields within the compact core. By applying the flux freezing approximation, we estimated the magnetic flux carried by the jet. We found that it reaches or exceeds theoretical predictions for jets powered by black hole spin energy via the Blandford-Znajek mechanism. This implies that OH 471 is in a magnetically arrested disk (MAD) state, where the magnetic flux accumulated near the horizon regulates the accretion flow, allowing for an efficient extraction of black hole rotational energy.

Conclusions. Our study demonstrates the dominance of MAD accretion in powering the prominent radio flares and relativistic jets observed in the radio-loud AGN named OH 471. Statistical studies of larger samples of high-redshift AGNs will shed light on the role of MAD accretion in launching and accelerating the earliest relativistic jets.