Description
Polarisation measurements of gamma-ray burst afterglows provide a powerful tool for probing the structure of relativistic jets.
In this talk, I will discuss polarisation signatures of gamma-ray burst afterglows, emphasising deviations from the classical model for axisymmetric top-hat jets, which predicts two polarisation peaks and a 90-degree position angle rotation.
Observations of events, such as GRB 170817A have demonstrated that GRB jets can be structured, with the late-time afterglow consistent with a structured jet viewed off-axis.
Structured jets will typically show a single peak in the afterglow along with an unchanging position angle.
Using a toy model we developed; we examine polarisation signals for non-axisymmetric top-hat and structured jets. For non-axisymmetric top-hat jets, the polarisation curve maintains the two-peak structure but no longer drops to zero in-between, and position angle rotations can deviate significantly from 90 degrees. Structured non-axisymmetric jets exhibit a single peak and a gradually evolving position angle.
I will also briefly explore the implications for GRB events with non-standard polarisation angle rotations such as GRB 210610B in which a $54 \pm 9$ degree rotation was observed near a break in the light curve.
Jet asymmetry also leaves a signature on the afterglow light curve; the possibility of constraining the jet’s geometry from multiple breaks observed in the light curve will be discussed.
