The brightest GRB ever detected: GRB 221009A as a highly luminous event at z = 0.151

¹ Department of Astrophysics/IMAPP, Radboud University, 6525 AJ Nijmegen, The Netherlands
² Cosmic Dawn Center (DAWN), Copenhagen, Denmark
³ Niels Bohr Institute, University of Copenhagen, Jagtvej 128, 2200 Copenhagen N, Denmark
⁴ Department of Physics, University of Warwick, CV4 7AL Coventry, United Kingdom
⁵ DARK, Niels Bohr Institute, University of Copenhagen Jagtvej 128, 2200 Copenhagen N, Denmark
⁶ Artemis, Université Côte d’Azur, Observatoire de la Côte d’Azur, CNRS, F-06304 Nice, France
⁷ INAF, Osservatorio Astronomico di Brera, via E. Bianchi 46, I-23807 Merate (LC), Italy
⁸ INFN – Sezione di Milano-Bicocca, Piazza della Scienza 3, I-20146 Milano (MI), Italy
⁹ Hessian Research Cluster ELEMENTS, Giersch Science Center, Max-von-Laue-Strasse 12, Goethe University Frankfurt, Campus Riedberg, 60438 Frankfurt am Main, Germany
¹⁰ Astrophysics Research Institute, Liverpool John Moores University, 146 Brownlow Hill, Liverpool L3 5RF, UK
¹¹ GEPI, Observatoire de Paris, Université PSL, CNRS, 5 Place Jules Janssen, 92190 Meudon, France
¹² INAF, Istituto di Astrofisica Spaziale e Fisica cosmica, Via Alfonso Corti 12, I-20133 Milano (MI), Italy
¹³ School of Physics and Astronomy, University of Leicester, University Road, LE1 7RH Leicester, United Kingdom
¹⁴ Instituto de Astrofísica de Andalucía – CSIC, Glorieta de la Astronomía s/n, 18008 Granada, Spain
¹⁵ European Space Agency (ESA), European Space Research and Technology Centre (ESTEC), Keplerlaan 1, 2201 AZ Noordwijk, The Netherlands
¹⁶ ASI – Italian Space Agency, Space Science Data Centre, Via del Politecnico snc, 00133 Rome, Italy
¹⁷ INAF, Osservatorio Astronomico di Capodimonte, Salita Moiariello 16, 80131 Napoli, Italy
¹⁸ Department of Mathematics, Informatics, Physics and Earth Sciences, University of Messina, Via F. D’Alcontres 31, Papardo, Messina 98166, Italy
¹⁹ School of Physics and Astronomy & Institute for Gravitational Wave Astronomy, University of Birmingham, Birmingham B15 2TT, United Kingdom
²⁰ Department of Physics and Astronomy, Kinard Lab of Physics, Clemson University, Clemson, SC 29634, USA
²¹ Centre for Astrophysics and Cosmology, Science Institute, University of Iceland, Dunhagi 5, 107 Reykjavík, Iceland
²² INAF–Osservatorio di Astrofisica e Scienza dello Spazio, Via Piero Gobetti 93/3, 40024 Bologna, Italy
²³ Astronomical Institute Anton Pannekoek, University of Amsterdam, 1090 GE Amsterdam, The Netherlands
²⁴ Department of Physics, University of Bath, Bath BA2 7AY, United Kingdom
²⁵ Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology, 77 Massachusetts Ave, Cambridge, MA 02139, USA
²⁶ The Oskar Klein Centre, Department of Astronomy, Stockholm University, AlbaNova, SE-106 91 Stockholm, Sweden
²⁷ Astronomical Institute of the Czech Academy of Sciences, Fričova 298, 251 65 Ondřejov, Czech Republic
²⁸ Department of Physics, George Washington University, 725 21st St NW, Washington, DC 20052, USA
²⁹ Physics Department, Lancaster University, Lancaster LA1 4YB, United Kingdom
³⁰ Key Laboratory of Space Astronomy, National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100101, China
³¹ School of Mathematical and Physical Sciences, Macquarie University, NSW 2109, Australia

^⋆ Corresponding author: d.malesani@astro.ru.nl

Received: 15 February 2023
Accepted: 9 June 2024

Abstract

Context. The extreme luminosity of gamma-ray bursts (GRBs) makes them powerful beacons, thus effective probes of the distant Universe. The most luminous bursts are typically detected at moderate and high redshift, where the volume for seeing such rare events is maximized and the star-formation activity is greater than at z = 0. For distant events, not all observations are feasible, such as those at TeV energies.

Aims. Here we present a spectroscopic redshift measurement for the exceptional GRB 221009A, the brightest GRB observed to date, with emission extending well into the TeV regime.

Methods. We used the X-shooter spectrograph at the ESO Very Large Telescope (VLT) to obtain simultaneous optical to near-infrared (NIR) spectroscopy of the burst afterglow 0.5 days after the explosion.

Results. The spectra exhibit both absorption and emission lines from material in a host galaxy at z_GRB = 0.15095 ± 0.00005. Thus, GRB 221009A was a relatively nearby burst with a luminosity distance of d_L = 745 Mpc. Its host galaxy properties (star-formation rate and metallicity) are consistent with those of long GRB hosts at low redshift. This redshift measurement yields information on the energy of the burst. The inferred isotropic energy release, E_iso > 5 × 10⁵⁴ erg, lies at the high end of the distribution, making GRB 221009A one of the nearest and also most energetic GRBs observed to date. We estimate that such a combination (nearby as well as intrinsically bright) occurs between once every few decades and once per millennium.