Ten per cent polarized optical emission from GRB 090102.
The nature of the jets and the role of magnetic fields in gamma-ray bursts (GRBs) remains unclear. In a baryon-dominated jet only weak, tangled fields generated in situ through shocks would be present. In an alternative model, jets are threaded with large-scale magnetic fields that originate at the central engine and that accelerate and collimate the material. To distinguish between the models the degree of polarization in early-time emission must be measured; however, previous claims of gamma-ray polarization have been controversial. Here we report that the early optical emission from GRB 090102 was polarized at 10 +/- 1 per cent, indicating the presence of large-scale fields originating in the expanding fireball. If the degree of polarization and its position angle were variable on timescales shorter than our 60-second exposure, then the peak polarization may have been larger than ten per cent.
Steele
I A
IA
Astrophysics Research Institute, Liverpool John Moores University, CH41 1LD, UK. ias@astro.livjm.ac.uk
Mundell
C G
CG
Smith
R J
RJ
Kobayashi
S
S
Guidorzi
C
C