The expansion of the GRB 221009A afterglow
Journal article, 2024
We observed γ-ray burst (GRB) 221009A using very long baseline interferomety (VLBI) with the European VLBI Network (EVN) and the Very Long Baseline Array (VLBA), over a period spanning from 40 to 262 days after the initial GRB. The high angular resolution (mas) of our observations allowed us, for the second time ever, after GRB 030329, to measure the projected size, s, of the relativistic shock caused by the expansion of the GRB ejecta into the surrounding medium. Our observations support the expansion of the shock with a > 4σ-equivalent significance, and confirm its relativistic nature by revealing an apparently superluminal expansion rate. Fitting a power law expansion model, s α ta, to the observed size evolution, we find a slope a = 0.69α' 0.14+0.13. Fitting the data at each frequency separately, we find different expansion rates, pointing to a frequency-dependent behaviour. We show that the observed size evolution can be reconciled with a reverse shock plus forward shock, provided that the two shocks dominate the emission at different frequencies and, possibly, at different times.
Techniques: interferometric
Radio continuum: general
Gamma-ray burst: individual: GRB 221009A
Techniques: high angular resolution
Gamma-ray burst: general
Author
S. Giarratana
University of Bologna
Istituto di Radioastronomia
O. S. Salafia
National Institute for Nuclear Physics
Istituto nazionale di astrofisica (INAF)
M. Giroletti
Istituto di Radioastronomia
G. Ghirlanda
National Institute for Nuclear Physics
Istituto nazionale di astrofisica (INAF)
L. Rhodes
University of Oxford
P. Atri
Netherlands Institute for Radio Astronomy (ASTRON)
B. Marcote
Joint Institute for Very Long Baseline Interferometry European Research Infrastructure Consortium (JIVE)
Jun Yang
Chalmers, Space, Earth and Environment, Onsala Space Observatory
T. An
Chinese Academy of Sciences
G. A. Anderson
International Centre for Radio Astronomy Research
J. S. Bright
University of Oxford
W. Farah
University of California
SETI Institute
R. P. Fender
University of Cape Town
University of Oxford
J. K. Leung
University of Toronto
The Hebrew University Of Jerusalem
S. E. Motta
University of Oxford
Istituto nazionale di astrofisica (INAF)
M.A. Pérez-Torres
Spanish National Research Council (CSIC)
University of Zaragoza
European University Cyprus
A. J. van der Horst
George Washington University
Astronomy and Astrophysics
0004-6361 (ISSN) 1432-0746 (eISSN)
Vol. 690 A74Opticon RadioNet Pilot
European Commission (EC) (EC/H2020/101004719), 2021-03-01 -- 2025-02-28.
Subject Categories (SSIF 2011)
Astronomy, Astrophysics and Cosmology
DOI
10.1051/0004-6361/202348524
Related datasets
URI: https://cdsarc.cds.unistra.fr/viz-bin/cat/J/ A+A/690/A74