Rotation of polarization angle in gamma-ray burst prompt phase

TL;DR

This paper investigates how polarization angle rotations in gamma-ray burst prompt emissions can be explained by magnetic reconnection models, revealing their dependence on viewing geometry and emission region shape, with applications to specific GRB observations.

Contribution

It introduces a magnetic reconnection model to explain polarization angle rotations in GRB prompt emission, emphasizing the role of observed shape changes of the emitting region.

Findings

PA rotations depend on off-axis viewing angles.

The model explains violent PA variations in GRB 170101A.

It cannot fully account for 90-degree PA flips in GRB 170114A.

Abstract

The rotations of the polarization angle (PA) with time (energy) can lead to the depolarization of the time-integrated (energy-integrated) polarization. However, we don't know how and when it will rotate. Here, we consider the magnetic reconnection model to investigate the polarizations, especially the PA rotations of GRB prompt emission. For the large-scale ordered aligned magnetic field configuration, we find that PAs will evolve with time (energy) for off-axis observations. Our studies show that the rotations of the PAs are due to the changes of the ``observed shape'' of the emitting region (before averaged). We apply our models to the single pulse burst of GRB 170101A and GRB 170114A with time-resolved PA observations. We find it can interpret the violent PA variation of GRB 170101A. The model could not predict the twice $90^{\circ}$ PA changes in GRB 170114A. Detailed model should be considered.