Issue |
A&A
Volume 690, October 2024
|
|
---|---|---|
Article Number | A216 | |
Number of page(s) | 17 | |
Section | Extragalactic astronomy | |
DOI | https://doi.org/10.1051/0004-6361/202348572 | |
Published online | 10 October 2024 |
Varying linear polarisation in the dust-free gamma-ray burst 210610B
1
Instituto de Astrofísica de Andalucía, Glorieta de la Astronomía s/n, 18008 Granada, Spain
2
Observatoire de la Côte d’Azur, Université Côte d’Azur, Boulevard de l’Observatoire, 06304 Nice, France
3
Aix Marseille Univ., CNRS, CNES, LAM, Marseille, France
4
Astronomical Institute of the Czech Academy of Sciences (ASU-CAS), Fričova 298, 251 65 Ondřejov, Czech Republic
5
Astrophysics Research Institute, Liverpool John Moores University, 146 Brownlow Hill, Liverpool L3 5RF, UK
6
INAF – Osservatorio di Astrofisica e Scienza dello Spazio, Via Piero Gobetti 93/3, 40129 Bologna, Italy
7
Frontier Research Institute for Interdisciplinary Sciences, Tohoku University, Sendai 980-8578, Japan
8
Astronomical Institute, Graduate School of Science, Tohoku University, Sendai 980-8578, Japan
9
Hessian Research Cluster ELEMENTS, Giersch Science Center, Max-von-Laue-Strasse 12, Goethe University Frankfurt, Campus Riedberg, 60438 Frankfurt am Main, Germany
10
INAF – Brera Astronomical Observatory, Merate, Italy
11
Centre for Astrophysics Research, University of Hertfordshire, Hatfield AL10 9AB, UK
12
Clemson University, Department of Physics and Astronomy, Clemson, SC 29634, USA
13
Centre for Astrophysics and Cosmology, Science Institute, University of Iceland, Dunhagi 5, 107 Reykjavík, Iceland
14
School of Physics and Centre for Space Research, O’Brien Centre for Science North, University College Dublin, Belfield, Dublin 4, Ireland
15
INAF – Rome Astronomical Observatory, Via Frascati 33, I-00078 Monte Porzio Catone, Italy
16
University of Messina, MIFT Department, Via F. S. D’Alcontres 31, 98166 Messina, Italy
17
Astronomical Institute Anton Pannekoek, University of Amsterdam, PO Box 94249 1090 GE Amsterdam, The Netherlands
18
Physics Department, University of Calabria, Via P. Bucci, 87036 Arcavacata di Rende, CS, Italy
19
INFN-Laboratori Nazionali di Frascati, Via Enrico Fermi 54, 00044 Frascati, RM, Italy
20
School of Physics and Astronomy, University of Leicester, University Road, Leicester LE1 7RH, UK
21
Capodimonte Astronomical Observatory, INAF-Napoli, Salita Moiariello 16, 80131 Napoli, Italy
22
Inter-University Institute for Data Intensive Astronomy & Department of Astronomy, University of Cape Town, Private Bag X3, Rondebosch 7701, South Africa
23
School of Mathematical and Physical Sciences, Macquarie University, Macquarie, NSW 2109, Australia
24
ARC Centre of Excellence for All Sky Astrophysics in 3 Dimensions (ASTRO-3D), Australia
Received:
12
November
2023
Accepted:
23
February
2024
Context. Long gamma-ray bursts (GRBs) are produced by the collapse of some very massive stars, that emit ultra-relativistic jets. When the jets collide with the interstellar medium they decelerate and generate the so-called afterglow emission, which has been observed to be polarised.
Aims. We study the polarimetric evolution of the GRB 210610B afterglow, at z = 1.1341. This allows us to evaluate the role of geometric and/or magnetic mechanisms in the GRB afterglow polarisation.
Methods. We observed GRB 210610B using imaging polarimetry with CAFOS on the 2.2 m Calar Alto Telescope and FORS2 on the 4 × 8.1 m Very Large Telescope. Complementary optical spectroscopy was obtained with OSIRIS on the 10.4 m Gran Telescopio Canarias. We studied the GRB light-curve from X-rays to the optical bands and the Spectral Energy Distribution (SED). This allowed us to strongly constrain the line-of-sight extinction. Finally, we studied the GRB host galaxy using optical to NIR data to fit the SED and derive its integrated properties.
Results. GRB 210610B had a bright afterglow with a negligible line-of-sight extinction. Polarimetry was obtained at three epochs: during an early plateau phase, at the time when the light curve breaks, and after the light curve steepened. We observe an initial polarisation of ∼4% that goes to zero at the time of the break, and it then again increases to ∼2%, with a change in the position angle of 54 ± 9 deg. The spectrum shows features with very low equivalent widths. This indicate a small amount of material in the line of sight within the host.
Conclusions. The lack of dust and the low amount of material in the line of sight to GRB 210610B allowed us to study the intrinsic polarisation of the GRB optical afterglow. The GRB polarisation signals are consistent with ordered magnetic fields in refreshed shock or/and hydrodynamics-scale turbulent fields in the forward shock.
Key words: polarization / techniques: polarimetric / gamma-ray burst: individual: GRB 210610B
© The Authors 2024
Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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