J/A+A/671/A116 GRB 210731A flux measurements (de Wet+, 2023)
The triple-peaked afterglow of GRB 210731A from X-ray to radio frequencies.
de Wet S., Laskar T., Groot P.J., Cavallaro F., Nicuesa Guelbenzu A.,
Chastain S., Izzo L., Levan A., Malesani D.B., Monageng I.M.,
van der Horst A.J., Zheng W., Bloemen S., Filippenko A.V., Kann D.A.,
Klose S., Pieterse D.L.A., Rau A., Vreeswijk P.M., Woudt P., Zhu Z.-P.
<Astron. Astrophys. 671, A116 (2023)>
=2023A&A...671A.116D 2023A&A...671A.116D (SIMBAD/NED BibCode)
ADC_Keywords: GRB ; Equivalent widths ; X-ray sources ; Radio sources ; Optical
Keywords: gamma-ray burst: individual: GRB 210731A
Abstract:
GRB 210731A was a long-duration (T90=22.5s) gamma-ray burst
discovered by the Burst Alert Telescope aboard the Neil Gehrels Swift
Observatory. Swift triggered the wide-field, robotic MeerLICHT optical
telescope in Sutherland, which began observing the BAT error circle
286 seconds after the Swift trigger and discovered the optical
afterglow of GRB 210731A in its first 60 second q-band exposure.
Multi-colour observations of the afterglow with MeerLICHT revealed a
light curve showing three peaks of similar brightness within the first
four hours. The unusual optical evolution prompted multi-wavelength
follow-up observations spanning X-ray to radio frequencies. We present
the results of our follow-up campaign and interpret our observations
in the framework of the synchrotron forward shock model. We perform
temporal and spectral fits to determine the spectral regime and
external medium density profile, and perform detailed multi-wavelength
theoretical modelling of the afterglow following the last optical peak
at ∼0.2 days to determine the intrinsic blast wave parameters. We find
a preference for a stellar wind density profile consistent with a
massive star origin, while our theoretical modelling results in fairly
typical shock microphysics parameters. Based on the energy released in
gamma-rays and the kinetic energy in the blast wave we determine a low
radiative efficiency of ∼0.02. The first peak in the optical light
curve is likely the onset of the afterglow, while we find that energy
injection into the forward shock offers the simplest explanation for
the subsequent light curve evolution, with the blast wave kinetic
energy increasing by a factor of ∼1000 from the first peak to the last
peak, indicative of substantial energy injection. Our
highest-likelihood theoretical model over-predicts the 1.4GHz flux by
a factor of approximately three with respect to our upper limits,
possibly implying a population of thermal electrons within the shocked
region.
Description:
Table of flux measurements used in the paper, equivalent to Table B.1.
Objects:
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RA (2000) DE Designation(s)
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20 01 13.13 -28 03 39.7 GRB 210731A = GRB 210731A
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
tableb1.dat 53 222 GRB 210731A flux measurements
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Byte-by-byte Description of file: tableb1.dat
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Bytes Format Units Label Explanations
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1- 9 F9.5 d Time Time in days since the Swift trigger
11- 20 A10 --- Tel Name of telescope
22- 26 A5 --- Band Name of the observing band or filter (1)
28- 36 E9.3 Hz Freq Observing band frequency
38- 44 F7.3 uJy Flux Measured flux
46- 51 F6.3 uJy e_Flux Measured flux error
53 I1 --- l_Flux [0/1] 1 denotes detections,
0 denotes upper limits
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Note (1): band or filter are C, H, J, K, L, X, b, g, i, q, r, u, v, z,
g', i', r', z', 1keV, uvm2, uvw1, uvw2, clear and white.
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Acknowledgements:
Simon de Wet, DWTSIM002(at)myuct.ac.za
(End) Patricia Vannier [CDS] 26-Jan-2023