The most distant optically polarised GRB afterglow: GRB 240419A at z = 5.178
Year: 2025
Type: article
Abstract: Context. Gamma-ray bursts (GRBs) are extremely bright phenomena powered by relativistic jets arising from explosive events at cosmological distances. The nature of the jet and the configuration of the local magnetic fields are still unclear, with the distinction between different models possibly provided by the detection of early-time polarisation. Aims. Past observations do not agree on a universal scenario describing early-time polarisation in GRB afterglows, and new studies are necessary to investigate this open question. We present here the discovery of GRB 240419A, its redshift determination of z = 5.178, its early-time optical polarimetry observations, and the multi-wavelength monitoring of its afterglow. Methods. We analysed three epochs of polarimetric data to derive the early-time evolution of the polarisation. The multi-wavelength light curve from the X-rays to the near-infrared band was also investigated to give a broader perspective on the whole event. Results. We find a high level of polarisation, P = 6.97 +1.84 −1.52 %, at 1740 s after the GRB trigger, followed by a slight decrease up to P = 4.81 +1.87 −1.53 % at 3059 s. On the same timescale, the polarisation position angle is nearly constant. The multi-band afterglow at the time of the polarisation measurements is consistent with a forward shock (FS), while the earlier evolution at t − t 0 ≲ 700 s can be associated with the interplay between the forward and the reverse shocks or with energy injection. Conclusions. The detected polarised radiation when the afterglow is FS-dominated and the stable position angle are consistent with an ordered magnetic field plus a turbulent component driven by large-scale magnetohydrodynamic instabilities. The lack of a jet break in the light curve prevents a comparison of the polarisation temporal evolution with theoretical expectations from magnetic fields amplified by microscopic-scale turbulence, limiting our ability to constrain the observer’s viewing angle. Notably, GRB 240419A is the most distant GRB with a detected polarised optical afterglow, extending the redshift range for such measurements.
Source: Astronomy and Astrophysics
Authors: R. Brivio, S. Covino, M. Ferro, A. Saccardi, A. Martin-Carrillo, A. Kuwata, K. Toma, P. D’Avanzo, Y.-D. Hu, L. Izzo, S. Kobayashi, T. Laskar, G. Leloudas, D. B. Malesani, M. Pursiainen, S. Vergani, K. Wiersema, S. Bloemen, S. Campana, V. D’Elia, S. de Wet, M. de Pasquale, P. J. Groot, P. Jakobsson, J. Mao, A. Melandri, G. Pugliese, A. Rossi, R. Salvaterra, B. Schneider, N. R. Tanvir, J. van Roestel, P. M. Vreeswijk, T. Zafar
Institutions: Brera Astronomical Observatory, National Institute for Astrophysics, University of Insubria, Centre National de la Recherche Scientifique, Université Paris Cité, Commissariat à l'Énergie Atomique et aux Énergies Alternatives, Université Paris-Saclay, Astrophysique, Instrumentation et Modélisation, University College Dublin, Tohoku University, Frontier Research Institute for Interdisciplinary Sciences, Tohoku University, Guangxi University, Astronomical Observatory of Capodimonte, Liverpool John Moores University, University of Utah, DTU Space, Technical University of Denmark, University of Copenhagen, Radboud University Nijmegen, University of Warwick, Université Paris Sciences et Lettres, Observatoire de Paris, Sorbonne Université, University of Hertfordshire, Agenzia Spaziale Italiana, University of Messina, University of Cape Town, Inter-university Institute for Data Intensive Astronomy, South African Astronomical Observatory, University of Iceland, Chinese Academy of Sciences, Yunnan Observatories, Astronomical Observatory of Rome, University of Amsterdam, Osservatorio di Astrofisica e Scienza dello Spazio, Aix-Marseille Université, Massachusetts Institute of Technology, University of Leicester, Macquarie University
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: gold
Estimated APC paid: $1,865
Funders: Texas Tech University, Villum Fonden, UK Research and Innovation, University of Leicester, University of Warwick, University of Oxford, Durham University, Weizmann Institute of Science, National Natural Science Foundation of China, Universiteit van Amsterdam, Radboud Universiteit, Centre National d’Etudes Spatiales, Ministero dell’Istruzione, dell’Università e della Ricerca, Hebrew University of Jerusalem, Agenzia Spaziale Italiana, KU Leuven, Universität Potsdam, Tel Aviv University, Danmarks Tekniske Universitet, Universitat de Barcelona, University of Cape Town, National Natural Science Foundation of China-Yunnan Joint Fund
OpenAlex ID: W4414644116