2022A&A...666A.179B


Query : 2022A&A...666A.179B

2022A&A...666A.179B - Astronomy and Astrophysics, volume 666A, 179 (2022/10-1)

GRB 080928 afterglow imaging and spectro-polarimetry.

BRIVIO R., COVINO S., D'AVANZO P., WIERSEMA K., MAUND J.R., BERNARDINI M.G., CAMPANA S. and MELANDRI A.

Abstract (from CDS):


Context. Among the large variety of astrophysical sources that we can observe, gamma-ray bursts (GRBs) are the most energetic of the whole Universe. Their emission peaks in the γ-ray band, with a duration from a fraction of a second to a few hundred seconds, and is followed by an afterglow covering the whole electromagnetic spectrum. The definition of a general picture describing the physics behind GRBs has always been a compelling task, but the results obtained so far from observations have revealed a puzzling landscape. The lack of a clear, unique paradigm calls for further observations and additional, independent techniques for this purpose. Polarimetry constitutes a very useful example as it allows us to investigate some features of the source such as the geometry of the emitting region and the magnetic field configuration.
Aims. To date, only a handful of bursts detected by space telescopes have been accompanied by ground-based spectro-polarimetric follow-up, and therefore such an analysis of more GRBs is of crucial importance in order to increase the sample of bursts with multi-epoch polarisation analysis. In this work, we present the analysis of the GRB 080928 optical afterglow, with observations performed with the ESO-VLT FORS1 instrument.
Methods. Starting from raw data taken in the imaging polarimetry (IPOL) and spectro-polarimetry (PMOS) modes, we performed data reduction, followed by the photometric analysis of IPOL data, taken ∼14 and ∼40 h after the burst detection, and spectroscopy of PMOS data (t ∼ 14.95 h). After computing the reduced Stokes parameters Q/I and U/I, which describe the linear polarisation of the emitted radiation, we obtained the polarisation degree for the three observing epochs.
Results. We find that the GRB optical afterglow was not significantly polarised on the first observing night. The polarisation degree (P) grew on the following night to a level of P ∼ 4.5%, giving evidence of polarised radiation at a 4σ confidence level. The GRB 080928 light curve is not fully consistent with standard afterglow models, making any comparison with polarimetric models partly inconclusive. The most conservative interpretation is that the GRB emission was characterised by a homogeneous jet and was observed at an angle of 0.6 <θobsjet < 0.8. Moreover, the non-zero polarisation degree on the second night suggests the presence of a dominant locally ordered magnetic field in the emitting region.

Abstract Copyright: © R. Brivio et al. 2022

Journal keyword(s): gamma-ray burst: individual: GRB 080928 - polarization

Simbad objects: 23

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Number of rows : 23
N Identifier Otype ICRS (J2000)
RA
ICRS (J2000)
DEC
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2024
#notes
1 GRB 091208A gB 00 01 10.90 +65 40 47.7           ~ 23 0
2 GRB 041219 gB 00 24 27.7 +62 50 34           ~ 226 1
3 GRB 021004 gB 00 26 54.68 +18 55 41.6           ~ 548 0
4 NAME SMC G 00 52 38.0 -72 48 01   2.79 2.2     ~ 11178 1
5 GRB 091018 gB 02 08 46 -57 33.0           ~ 144 0
6 NAME Magellanic Clouds GrG 03 00 -71.0           ~ 7084 0
7 GRB 121024A gB 04 41 53.31 -12 17 26.1           ~ 121 0
8 NAME LMC G 05 23 34.6 -69 45 22     0.4     ~ 17478 0
9 NGC 2024 Cl* 05 41 43 -01 50.5           ~ 1154 1
10 Fermi bn080928628 gB 06 20 16.85 -55 11 59.3           ~ 166 0
11 GRB 090102 gB 08 32 59.50 +33 06 25.7           ~ 222 0
12 NAME Vela XYZ Rad 08 34.0 -45 50           ~ 1232 2
13 GRB 061121 gB 09 48 54.570 -13 11 42.68 17.19 17.71 17.02     ~ 327 0
14 GRB 191221B gB 10 19 19.17 -38 09 27.5           ~ 42 0
15 SN 2003dh SN* 10 44 50.030 +21 31 18.15     16.2     SNIcpec 1210 1
16 GRB 990510 gB 13 38 07.64 -80 29 48.8           ~ 489 1
17 GRB 120308A gB 14 36 20.02 +79 41 12.0           ~ 69 0
18 * alf Lyr dS* 18 36 56.33635 +38 47 01.2802 0.03 0.03 0.03 0.07 0.10 A0Va 2687 1
19 GRB 071010A gB 19 12 14.42 -32 24 06.2           ~ 125 0
20 GRB 020813A gB 19 46 41.874 -19 36 04.81           ~ 304 0
21 EGGR 150 WD* 21 52 25.3789636654 +02 23 19.576176425 11.942 12.732 12.743 12.839 12.938 DA2.8 195 0
22 GRB 050820A gB 22 29 38.110 +19 33 37.10 18.33 19.00 18.47     ~ 387 0
23 GRB 051111A gB 23 12 33.170 +18 22 28.80 19.77 20.08 19.50     ~ 207 0

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