2025MNRAS.543.1039B

Polarization measurements of gamma-ray burst afterglows provide a powerful tool for probing the structure of relativistic jets. In this study, we revisit polarization signals observed in gamma-ray burst afterglows, focusing on the effects of non-axisymmetric jet structures. To characterize these non-axisymmetric jets, we adopt a simple elliptical jet head model and investigate how deviations from axisymmetry influence the temporal evolution of polarization properties, particularly around the jet break. Our results show that the polarization degree curve typically exhibits two peaks for top-hat jets or a single peak for structured jets, even in the presence of an elliptical jet head. In non-axisymmetric jets, a complete drop in polarization between peaks is generally absent, and the position angle rotation between the peaks can deviate significantly from 90 deg. In single-peak cases, the polarization position angle evolves gradually, contrasting with the constant position angle expected in axisymmetric jets. We also explore the implications of these findings for recent gamma-ray burst (GRB) events, including GRB 121024A, GRB 091018, GRB 020813, and GRB 210610B.