A blast from the infant Universe: The very high-z GRB 210905A^⋆

¹ INAF – Osservatorio di Astrofisica e Scienza dello Spazio, Via Piero Gobetti 93/3, 40129 Bologna, Italy
e-mail: andrea.rossi@inaf.it
² Ioffe Institute, Politekhnicheskaya 26, St. Petersburg 194021, Russia
³ Instituto de Astrofísica de Andalucía (IAA-CSIC), Glorieta de la Astronomía s/n, 18008 Granada, Spain
⁴ University of Messina, MIFT Department, Polo Papardo, Viale F.S. D’Alcontres 31, 98166 Messina, Italy
⁵ School of Physics and Astronomy, University of Leicester, University Road, Leicester LE1 7RH, UK
⁶ INAF – Osservatorio Astronomico di Brera, Via E. Bianchi 46, 23807 Merate, LC, Italy
⁷ DARK, Niels Bohr Institute, University of Copenhagen, Jagtvej 128, 2200 Copenhagen, Denmark
⁸ Department of Astrophysics/IMAPP, Radboud University, 6525 AJ Nijmegen, The Netherlands
⁹ Cosmic DAWN Center, Denmark
¹⁰ Niels Bohr Institute, University of Copenhagen, Jagtvej 128, 2200 Copenhagen, Denmark
¹¹ Thüringer Landessternwarte Tautenburg, Sternwarte 5, 07778 Tautenburg, Germany
¹² The Oskar Klein Centre, Physics Department of Physics, Stockholm University, Albanova University Center, Stockholm, 106 91 SE, Sweden
¹³ University of the Virgin Islands, Number 2 Brewers Bay Rd., St. Thomas, VI 00802, USA
¹⁴ College of Marin, 120 Kent Avenue, Kentfield, CA 94904, USA
¹⁵ INFN – Sezione di Milano-Bicocca, Piazza della Scienza 3, 20126 Milano, Italy
¹⁶ INAF, Osservatorio Astronomico di Capodimonte, Salita Moiariello 16, 80131 Naples, Italy
¹⁷ INAF – IASF Milano, Via Alfonso Corti 12, 20133 Milano, Italy
¹⁸ INAF – Istituto di Astrofisica e Planetologia Spaziali, Via Fosso del Cavaliere 100, 00133 Roma, Italy
¹⁹ GEPI, Observatoire de Paris, PSL University, CNRS, 5 Place Jules Janssen, 92190 Meudon, France
²⁰ Institut d’Astrophysique de Paris, UMR 7095, CNRS-SU, 98 bis boulevard Arago, 75014 Paris, France
²¹ INAF – IASF Palermo, Via Ugo La Malfa 153, 90146 Palermo, Italy
²² Aix Marseille Univ, CNRS, CNES, LAM, Marseille, France
²³ Space Science Data Center (SSDC) – Agenzia Spaziale Italiana (ASI), 00133 Roma, Italy
²⁴ INAF – Osservatorio Astronomico di Roma, Via Frascati 33, 00040 Monte Porzio Catone, Italy
²⁵ Artemis, Observatoire de la Côte d’Azur, Université Côte d’Azur, CNRS, 06304 Nice, France
²⁶ Department of Physics, The George Washington University, 725 21st Street NW, Washington, DC 20052, USA
²⁷ Department of Physics and Earth Science, University of Ferrara, Via Saragat 1, 44122 Ferrara, Italy
²⁸ INFN – Sezione di Ferrara, Via Saragat 1, 44122 Ferrara, Italy
²⁹ Centre for Astrophysics and Cosmology, Science Institute, University of Iceland, Dunhagi 5, 107 Reykjavík, Iceland
³⁰ Departamento de Ciencias Físicas, Universidad Andrés Bello, Fernández Concha 700, Las Condes, Santiago, Chile
³¹ Department of Physics, University of Bath, Claverton Down, Bath BA2 7AY, UK
³² School of Physics and Astronomy and Institute for Gravitational Wave Astronomy, University of Birmingham, Birmingham B15 2TT, UK
³³ Mullard Space Science Laboratory, University College London, Holmbury St Mary, Dorking, Surrey RH5 6NT, UK
³⁴ Anton Pannekoek Institute for Astronomy, University of Amsterdam, Science Park 904, 1098 XH Amsterdam, The Netherlands
³⁵ Leiden Observatory, University of Leiden, Niels Bohrweg 2, 2333 CA Leiden, The Netherlands
³⁶ Max-Planck-Institut für Extraterrestrische Physik, Giessenbachstraße 1, 85748 Garching, Germany
³⁷ Department of Astronomy and Astrophysics, The Pennsylvania State University, University Park, PA 16802, USA
³⁸ Astronomy, Physics, and Statistics Institute of Sciences (APSIS), 725 21st Street NW, Washington, DC 20052, USA
³⁹ Physics Department, Lancaster University, Lancaster LA1 4YB, UK
⁴⁰ Key Laboratory of Space Astronomy and Technology, National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100101, PR China
⁴¹ School of Astronomy and Space Sciences, University of Chinese Academy of Sciences, 19A Yuquan Road, Beijing 100049, PR China
⁴² Centre for Astrophysics and Supercomputing, Swinburne University of Technology, Mail Number H29, PO Box 218, 31122 Hawthorn, VIC, Australia
⁴³ ARC Centre of Excellence for Gravitational Wave Discovery (OzGrav), Hawthorn 3122, Australia

Received: 30 January 2022
Accepted: 1 August 2022

Abstract

We present a detailed follow-up of the very energetic GRB 210905A at a high redshift of z = 6.312 and its luminous X-ray and optical afterglow. Following the detection by Swift and Konus-Wind, we obtained a photometric and spectroscopic follow-up in the optical and near-infrared (NIR), covering both the prompt and afterglow emission from a few minutes up to 20 Ms after burst. With an isotropic gamma-ray energy release of E_iso = 1.27_−0.19^+0.20 × 10⁵⁴ erg, GRB 210905A lies in the top ∼7% of gamma-ray bursts (GRBs) in the Konus-Wind catalogue in terms of energy released. Its afterglow is among the most luminous ever observed, and, in particular, it is one of the most luminous in the optical at t ≳ 0.5 d in the rest frame. The afterglow starts with a shallow evolution that can be explained by energy injection, and it is followed by a steeper decay, while the spectral energy distribution is in agreement with slow cooling in a constant-density environment within the standard fireball theory. A jet break at ∼46.2 ± 16.3 d (6.3 ± 2.2 d rest-frame) has been observed in the X-ray light curve; however, it is hidden in the H band due to a constant contribution from the host galaxy and potentially from a foreground intervening galaxy. In particular, the host galaxy is only the fourth GRB host at z > 6 known to date. By assuming a number density n = 1 cm⁻³ and an efficiency η = 0.2, we derived a half-opening angle of 8.4 ° ±1.0°, which is the highest ever measured for a z ≳ 6 burst, but within the range covered by closer events. The resulting collimation-corrected gamma-ray energy release of ≃1 × 10⁵² erg is also among the highest ever measured. The moderately large half-opening angle argues against recent claims of an inverse dependence of the half-opening angle on the redshift. The total jet energy is likely too large to be sustained by a standard magnetar, and it suggests that the central engine of this burst was a newly formed black hole. Despite the outstanding energetics and luminosity of both GRB 210905A and its afterglow, we demonstrate that they are consistent within 2σ with those of less distant bursts, indicating that the powering mechanisms and progenitors do not evolve significantly with redshift.