The Polarization Variability in the Optical Afterglow of GRB 990712

In a recent paper, Rol and colleagues present evidence for a variable polarization in the optical afterglow following the gamma-ray burst GRB 990712. The variation is highly significant, but the position angle appears to be time independent. Contrary to their conclusion, we point out that this can in fact be explained with existing afterglow models, namely, that of a laterally expanding jet.

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