J/A+A/690/A74 GRB 221009A afterglow reduced visibilities (Giarratana+, 2024)
The expansion of the GRB 221009A afterglow.
Giarratana S., Salafia O.S., Giroletti M., Ghirlanda G., Rhodes L., Atri P.,
Marcote B., Yang J., An T., Anderson G., Bright J.S., Farah W., Fender R.,
Leung J.K., Motta S.E., Perez-Torres M., van der Horst A.J.
<Astron. Astrophys. 690, A74 (2024)>
=2024A&A...690A..74G 2024A&A...690A..74G (SIMBAD/NED BibCode)
ADC_Keywords: GRB ; Interferometry ; VLBI ; Radio continuum
Keywords: techniques: high angular resolution - techniques: interferometric -
gamma-ray burst: general - radio continuum: general -
gamma-ray burst: individual: GRB 221009A
Abstract:
We observed gamma-ray burst (GRB) 221009A using very long baseline
interferometry (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>4sigma-equivalent significance, and confirm its relativistic nature
by revealing an apparently superluminal expansion rate. Fitting a
power law expansion model, s∼ta, to the observed size evolution, we
find a slope a=0.69+0.13-0.14. 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.
Description:
VLBI observations of GRB 221009A using the EVN and the VLBA are
presented. For each observation, calibrated visibilities are provided
as fits files.
Objects:
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RA (2000) DE Designation(s)
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19 13 03.84 +19 46 22.6 GRB 221009A = SWIFT J1913.1+1946
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
list.dat 109 9 List of fits visibilities files
fits/* . 9 Individual fits visibilities files
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Byte-by-byte Description of file: list.dat
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Bytes Format Units Label Explanations
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1- 9 F9.5 deg RAdeg Right Ascension of center (J2000)
10- 18 F9.5 deg DEdeg Declination of center (J2000)
20 I1 --- Nx Number of pixels along X-axis
22 I1 --- Ny Number of pixels along Y-axis
24 I1 --- Nz Number of pixels along Z-axis
26- 35 A10 "datime" Obs.date Observed date
37- 44 F8.5 GHz Freq Observed frequency
46- 50 I5 Kibyte size Size of FITS file
52- 62 A11 --- FileName Name of FITS file, in subdirectory fits
64-109 A46 --- Title Title of the FITS file
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Acknowledgements:
Stefano Giarratana, stefano.giarratana(at)inaf.it
(End) Stefano Giarratana [OAB, Italy], Patricia Vannier [CDS] 31-Jul-2024