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TwitterA&A 422, 121-128 (2004)
DOI: 10.1051/0004-6361:20035951
On the jet structure and magnetic field configuration of GRB 020813
D. Lazzati1, S. Covino2, J. Gorosabel3, 4, E. Rossi1, G. Ghisellini2, E. Rol5, J. M. Castro Cerón4, A. J. Castro-Tirado3, M. Della Valle6, S. di Serego Alighieri6, A. S. Fruchter4, J. P. U. Fynbo7, P. Goldoni8, J. Hjorth9, G. L. Israel10, L. Kaper5, N. Kawai11, E. Le Floc'h8, D. Malesani12, N. Masetti13, P. Mazzali14, 15, 16, F. Mirabel8, P. Møller17, S. Ortolani18, E. Palazzi13, E. Pian14, J. Rhoads4, G. Ricker19, J. D. Salmonson20, L. Stella10, G. Tagliaferri2, N. Tanvir21, E. van den Heuvel5, R. A. M. J. Wijers5 and F. M. Zerbi21 Institute of Astronomy, University of Cambridge, Madingley Road, CB3 0HA Cambridge, UK
2 INAF, Osservatorio Astronomico di Brera, via E. Bianchi 46, 23807 Merate (LC), Italy
3 Instituto de Astrofísica de Andalucía (IAA-CSIC), Apartado de Correos, 3004, 18080 Granada, Spain
4 Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218-2463, USA
5 University of Amsterdam, Kruislaan 403, 1098 SJ Amsterdam, The Netherlands
6 INAF, Osservatorio Astrofisico di Arcetri, Large E. Fermi 5, 50125 Firenze, Italy
7 Department of Physics and Astronomy, University of Århus, Ny Munkegade, 8000 Århus C, Denmark
8 CEA/DSM/DAPNIA, L'Orme des Merisiers, Bât. 709, 91191 Gif-sur-Yvette, France
9 Niels Bohr Institute, Astronomical Observatory, University of Copenhagen, Juliane Maries Vej 30, 2100 Copenhagen Ø, Denmark
10 INAF, Osservatorio Astronomico di Roma, via Frascati 33, 00044 Monterporzio, Italy
11 Department of Physics, Faculty of Science, Tokyo Institute of Technology 2-12-1 Ookayama, Meguro-ku, Tokyo 152-8551, Japan
12 International School for Advanced Studies (SISSA/ISAS), via Beirut 2-4, 34014 Trieste, Italy
13 Istituto di Astrofisica Spaziale e Fisica Cosmica - Sezione di Bologna, CNR, Via Gobetti 101, 40129 Bologna, Italy
14 INAF, Osservatorio Astronomico di Trieste, Via Tiepolo 11, 34131 Trieste, Italy
15 Department of Astronomy, University of Tokyo, Bunkyo-ku, Tokyo 113-0033, Japan
16 Research Center for the Early Universe, University of Tokyo, Bunkyo-ku, Tokyo 113-0033, Japan
17 European Southern Observatory, Karl-Schwarzschild-Straße 2, 85748 Garching, Germany
18 Università di Padova, Dip. di Astronomia, Vicolo dell'Osservatorio 2, 35122 Padova, Italy
19 Center for Space Research, Massachusetts Institute of Technology, Cambridge, MA 02139-4307, USA
20 Lawrence Livermore National laboratory, L-038, PO Box 808, Livermore, CA, 94551, USA
21 Department of Physical Sciences, University of Hertfordshire, College Lane, Hatfield, Herts AL10 9AB, UK
(Received 28 December 2003 / Accepted 5 May 2004)
Abstract
The polarization curve of GRB 020813 is discussed and
compared to different models for the structure, evolution and
magnetisation properties of the jet and the interstellar medium onto
which the fireball impacts. GRB 020813 is best suited for this kind of
analysis for the smoothness of its afterglow light curve, ensuring the
applicability of current models. The polarization dataset allows us to
rule out the standard GRB jet, in which the energy and Lorentz factor
have a well defined value inside the jet opening angle and the
magnetic field is generated at the shock front. We explore alternative
models finding that a structured jet or a jet with a toroidal
component of the magnetic field can fit equally well the polarization
curve. Stronger conclusions cannot be drawn due to the incomplete
sampling of the polarization curve. A more dense sampling, especially
at early times, is required to pin down the structure of the jet and
the geometry of its magnetic field.
Key words: gamma rays: bursts -- polarization -- radiation mechanisms: non-thermal
Offprint request: D. Lazzati, lazzati@ast.cam.ac.uk
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