Early Optical Polarization of a Gamma Ray Burst Afterglow

Abstract

We report the optical polarization of a gamma ray burst (GRB) afterglow, obtained 203 seconds after the initial burst of gamma rays from GRB 060418, using a ring polarimeter on the robotic Liverpool Telescope. Our robust (2-sigma) upper limit on the percentage of polarization, less than 8%, coincides with the fireball deceleration time at the onset of the afterglow. The combination of the rate of decay of the optical brightness and the low polarization at this critical time constrains standard models of GRB ejecta, ruling out the presence of a large-scale ordered magnetic field in the emitting region.

8 pages including 1 figure. Accepted for publication in Science; published online 15 March 2007; 10.1126/science.1138484

References in corpus (2)

• Gravitational Lens Time Delays: A Statistical Assessment of Lens Model Dependences and Implications for the Global Hubble Constant
• Evolution of the polarization of the optical afterglow of the gamma-ray burst GRB 030329

Cited by in corpus (8)

• Deceleration of arbitrarily magnetized GRB ejecta: the complete evolution
• Multiwavelength analysis of the intriguing GRB 061126: the reverse shock scenario and magnetization
• The Early-time Optical Properties of Gamma-Ray Burst Afterglows
• GRB 060418 and 060607A: the medium surrounding the progenitor and the weak reverse shock emission
• On the existence of a reverse shock in magnetized GRB ejecta
• Rise and fall of the X-ray flash 080330: an off-axis jet?
• Interpretation and implication of the non-detection of GeV spectrum excess by Fermi gamma-ray Space Telescope in most GRBs
• A Closer Look at a Gamma-Ray Burst