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

Techniques: high angular resolution

Radio continuum: general

Gamma-ray burst: general

Gamma-ray burst: individual: GRB 221009A

Author

S. Giarratana

Istituto di Radioastronomia

University of Bologna

O. S. Salafia

Istituto nazionale di astrofisica (INAF)

National Institute for Nuclear Physics

M. Giroletti

Istituto di Radioastronomia

G. Ghirlanda

Istituto nazionale di astrofisica (INAF)

National Institute for Nuclear Physics

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

Shanghai Astronomical Observatory

Chinese Academy of Sciences

G. A. Anderson

International Centre for Radio Astronomy Research

J. S. Bright

University of Oxford

W. Farah

SETI Institute

University of California

R. P. Fender

University of Cape Town

University of Oxford

J. K. Leung

University of Toronto

The Hebrew University Of Jerusalem

S. E. Motta

Istituto nazionale di astrofisica (INAF)

University of Oxford

M.A. Pérez-Torres

University of Zaragoza

Institute of Astrophysics of Andalusia (IAA)

European University Cyprus

A. J. van der Horst

George Washington University

Astronomy and Astrophysics

0004-6361 (ISSN) 1432-0746 (eISSN)

Vol. 690 A74

Opticon RadioNet Pilot

European Commission (EC) (EC/H2020/101004719), 2021-03-01 -- 2025-02-28.

Subject Categories

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

More information

Latest update

11/5/2024