The nature of the jets and the role of magnetic fields in gamma-ray bursts (GRBs) remain unclear. There are two possible models, one of which suggests that magnetic fields are critical; to distinguish between these models the degree of polarization in early-time emission must be measured. The early optical emission from GRB 090102 is now reported to be polarized at 10 ± 1 per cent, indicating the presence of large-scale fields originating in the expanding fireball.
- I. A. Steele
- C. G. Mundell
- C. Guidorzi
