J/A+A/690/A216 GRB210610B polarization images (Agui Fernandez+, 2024)
Varying linear polarisation in the dust-free gamma-ray burst 210610B.
Agui Fernandez J.F., de Ugarte Postigo A., Thoene C.C., Kobayashi S.,
Rossi A., Toma K., Jelinek M., Kann D.A., Covino S., Wiersema K.,
Hartmann D., Jakobsson P., Martin-Carrillo A., Melandri A., De Pasquale M.,
Pugliese G., Savaglio S., Starling R.L.C., Strobl J., Della Valle M.,
de Wet S., Zafar T.
<Astron. Astrophys. 690, A216 (2024)>
=2024A&A...690A.216A 2024A&A...690A.216A (SIMBAD/NED BibCode)
ADC_Keywords: GRB ; Polarization
Keywords: polarisation - techniques: polarimetric -
gamma-ray bursts: individual: GRB210610B
Abstract:
Long gamma ray bursts (GRBs) are produced by the collapse of some very
massive stars, which 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.
In this work we study the polarimetric evolution of GRB 210610B
afterglow, at z=1.1341. This allows to evaluate the role of geometric
and/or magnetic mechanisms in the GRB afterglow polarisation. We
observed GRB 210610B using imaging polarimetry with CAFOS on the 2.2 m
Calar Alto Telescope and FORS2 on the 4x8.1m Very Large Telescope.
Complementary optical spectroscopy was obtained with OSIRIS on the
10.4m Gran Telescopio Canarias. We study the GRB light-curve from
X-rays to optical bands and the Spectral Energy Distribution (SED).
This allows us to strongly constrain the line-of-sight extinction.
Finally, we study the GRB host galaxy using optical/NIR data to fit
the SED and derive its integrated properties. 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 then increases again to ∼2% with a change of the
position angle of 54±9deg. The spectrum show features with very low
equivalent widths, indicating a small amount of material in the
line-of-sight within the host. The lack of dust and the low amount of
material on the line-of-sight to GRB 210610B allow us to study the
intrinsic polarisation of the GRB optical afterglow. We find the GRB
polarisation signals are consistent with ordered magnetic fields in
refreshed shock or/and hydrodynamics-scale turbulent fields in the
forward shock.
Description:
Polarimetry images of GRB210610B from the CAFOS instrument at CAHA
2.2m telescope. High and zero polarised standard stars are included.
Objects:
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RA (2000) DE Designation(s)
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16 15 40.47 +14 23 56.2 GRB210610B = Fermi bn210610827
15 51 59.88 +32 56 54.3 BD+33 2642 = HIP 77716
20 23 28.53 +39 20 59.0 Hiltner 960 = BD+38 4058
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
list.dat 145 12 List of fits images
fits/* . 12 Individual fits images
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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- 10 F10.6 deg RAdeg Right Ascension of center (J2000)
11- 19 F9.5 deg DEdeg Declination of center (J2000)
21- 23 I3 --- Nx Number of pixels along X-axis
25- 28 I4 --- Ny Number of pixels along Y-axis
30- 48 A19 "datime" Obs.date Observation date
50- 53 I4 Kibyte size Size of FITS file
55- 96 A42 --- FileName Name of FITS file, in subdirectory fits
98-145 A48 --- Title Title of the FITS file
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Acknowledgements:
Feli Agui Fernandez, feli.agui.fernandez(at)gmail.com
(End) Patricia Vannier [CDS] 01-Oct-2024