Polarization of gamma-ray burst afterglows in the context of non-axisymmetric structured jets

TL;DR

This paper investigates how non-axisymmetric jet structures in gamma-ray burst afterglows produce observable polarization signals, revealing complex polarization behaviors influenced by jet geometry, observation angle, and frequency.

Contribution

It provides the first detailed analysis of polarization characteristics in GRB afterglows with non-axisymmetric structured jets, highlighting their unique polarization signatures.

Findings

Polarization is generally present in afterglows with non-axisymmetric jets.

Polarization degree is higher when the line of sight is outside the jet.

Polarization angle can undergo abrupt changes at spectral breaks.

Abstract

As the most energetic explosion in the universe, gamma-ray bursts (GRBs) are usually believed to be generated by relativistic jets. Some mechanisms (e.g. internal non-uniform magnetic dissipation processes or the precession of the central engine) may generate asymmetric jet structures, which is characterized by multiple fluctuations in the light curve of afterglow. Since the jet's structure introduces asymmetry in radiation around the line of sight (LOS), it is naturally expected that polarization will be observable. In this work, we reveal the polarization characteristics of gamma-ray burst afterglows with a non-axisymmetric structured jet. Our results show that the afterglow signal generally exhibits polarization, with the degree and evolution influenced by the specific jet structure, observing frequency, and the line of sight (LOS). The polarization degree is notably higher when the LOS is outside the jet. This degree fluctuates over time as different regions of radiation alternate in their dominance, which is accompanied by the rotation of the polarization angle and further reflects the intricate nature of the jet. Regarding its evolution over frequency, the polarization degree displays significant fluctuations at spectral breaks, with the polarization angle possibly undergoing abrupt changes. These features may provide strong evidence for future identification of potential GRBs with asymmetric jet structures.