Report

Polarimetric Constraints on the Optical Afterglow Emission from GRB 990123

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Science  26 Mar 1999:
Vol. 283, Issue 5410, pp. 2073-2075
DOI: 10.1126/science.283.5410.2073

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Abstract

Polarization of the optical emission from GRB 990123 was measured on 24.17 January 1999 universal time with the Nordic Optical Telescope. An upper limit of 2.3% on the linear polarization was found. Accurate polarization measurements provide important clues to the blast wave geometry and magnetic field structure of gamma-ray bursts (GRBs). The lack of detectable polarization for GRB 990123 indicates that the optical afterglow was produced by a blast wave of unknown geometry with an insignificant coherent magnetic field or by a beamed outflow at high Lorentz factor seen at a small viewing angle. Such a collimated jet would help solve the problem of energy release in this exceptionally luminous cosmological burst.

  • * To whom correspondence should be addressed. E-mail: jens{at}astro.ku.dk

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