Comments on "Polarimetric constraints on the optical afterglow emission from GRB 990123" by Hjorth et al.
Received 24 March 2000 / Accepted 17 April 2000
Hjorth et al. (1999) reported an upper limit on the linear polarization of the optical afterglow for GRB 990123 (). One of the interpretations for this small value of P was that the emission was probably due a relativistic jet with ordered magnetic field, and the viewing angle in the lab frame , where is the bulk Lorentz factor of the jet. We point out that this conclusion is incorrect and resulted from a confusion between the angles measured in the lab frame () and in the plasma rest frame ().
Key words: gamma rays: bursts gamma rays: theory
© European Southern Observatory (ESO) 2000
Online publication: June 30, 2000