Letters to Nature

Nature 426, 157-159 (13 November 2003) | doi:10.1038/nature02077; Received 16 July 2003; Accepted 30 September 2003

Evolution of the polarization of the optical afterglow of the big gamma-ray burst GRB030329

Jochen Greiner1, Sylvio Klose2, Klaus Reinsch3, Hans Martin Schmid4, Re'em Sari5, Dieter H. Hartmann6, Chryssa Kouveliotou7, Arne Rau1, Eliana Palazzi8, Christian Straubmeier9, Bringfried Stecklum2, Sergej Zharikov10, Gaghik Tovmassian10, Otto Bärnbantner11, Christoph Ries11, Emmanuel Jehin12, Arne Henden13, Anlaug A. Kaas14, Tommy Grav15, Jens Hjorth16, Holger Pedersen16, Ralph A. M. J. Wijers17, Andreas Kaufer12, Hye-Sook Park18, Grant Williams19 & Olaf Reimer20

  1. Max-Planck-Institut für extraterrestrische Physik, 85741 Garching, Germany
  2. Thüringer Landessternwarte Tautenburg, 07778 Tautenburg, Germany
  3. Universitäts-Sternwarte Göttingen, 37083 Göttingen, Germany
  4. Institut für Astronomie, ETH Zürich, 8092 Zürich, Switzerland
  5. California Institute of Technology, Theoretical Astrophysics 130-33, Pasadena, California 91125, USA
  6. Clemson University, Department of Physics and Astronomy, Clemson, South Carolina 29634, USA
  7. NSSTC, SD-50, 320 Sparkman Drive, Huntsville, Alabama 35805, USA
  8. Istituto di Astrofisica Spaziale e Fisica Cosmica, CNR, Sezione di Bologna, 40129 Bologna, Italy
  9. Physikalisches Institut, Universität Köln, 50937 Köln, Germany
  10. Instituto de Astronomia, UNAM, 22860 Ensenada, Mexico
  11. Wendelstein-Observatorium, Universitätssternwarte, 81679 München, Germany
  12. European Southern Observatory, Alonso de Cordova 3107, Vitacura, Casilla 19001, Santiago 19, Chile
  13. Universities Space Research Association, US Naval Observatory, PO Box 1149, Flagstaff, Arizona 86002, USA
  14. Nordic Optical Telescope, 38700 Santa Cruz de La Palma, Spain
  15. University of Oslo, Institute for Theoretical Astrophysics, 0315 Oslo, Norway, and Harvard-Smithsonian Center for Astrophysics, Cambridge, Massachusetts 02138, USA
  16. Astronomical Observatory, NBIfAFG, University of Copenhagen, 2100 Copenhagen Ø, Denmark
  17. Astronomical Institute Anton Pannekoek, Kruislaan 403, 1098 SJ Amsterdam, The Netherlands
  18. Lawrence Livermore National Laboratory, University of California, PO Box 808, Livermore, California 94551, USA
  19. MMT Observatory, University of Arizona, Tucson, Arizona 85721, USA
  20. Theoretische Weltraum- und Astrophysik, Ruhr-Universität Bochum, 44780 Bochum, Germany

Correspondence to: Jochen Greiner1 Email: jcg@mpe.mpg.de

The association of a supernova with GRB0303291, 2 strongly supports the 'collapsar' model3 of gamma-ray bursts, where a relativistic jet4 forms after the progenitor star collapses. Such jets cannot be spatially resolved because gamma-ray bursts lie at cosmological distances; their existence is instead inferred from 'breaks' in the light curves of the afterglows, and from the theoretical desire to reduce the estimated total energy of the burst by proposing that most of it comes out in narrow beams. Temporal evolution of the polarization of the afterglows5, 6, 7 may provide independent evidence for the jet structure of the relativistic outflow. Small-level polarization (approx1–3 per cent)8, 9, 10, 11, 12, 13, 14, 15, 16, 17 has been reported for a few bursts, but its temporal evolution has yet to be established. Here we report polarimetric observations of the afterglow of GRB030329. We establish the polarization light curve, detect sustained polarization at the per cent level, and find significant variability. The data imply that the afterglow magnetic field has a small coherence length and is mostly random, probably generated by turbulence, in contrast with the picture arising from the high polarization detected in the prompt gamma-rays from GRB021206 (ref. 18).