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Astron. Astrophys. 359, 413 (2000)

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Comments on "Polarimetric constraints on the optical afterglow emission from GRB 990123" by Hjorth et al.

A. Mitra

Theoretical Physics Division, BARC, Mumbai, 400085, India

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 ([FORMULA]). 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 [FORMULA], where [FORMULA] 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 ([FORMULA]) and in the plasma rest frame ([FORMULA]).

Key words: gamma rays: bursts – gamma rays: theory

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© European Southern Observatory (ESO) 2000

Online publication: June 30, 2000