Polarization in early optical afterglows of gamma-ray bursts driven by precessing jets

TL;DR

This study investigates how jet precession in gamma-ray bursts influences the polarization of early optical afterglows, revealing that precession can significantly reduce polarization degree and offering insights into observed low polarization levels.

Contribution

It introduces a model incorporating jet precession to analyze polarization evolution in GRB afterglows with different magnetic field geometries, a novel approach in the field.

Findings

Jet precession reduces polarization degree in GRB afterglows.

Maximum polarization attenuation occurs when viewing along the precession axis.

Precession effects can explain low polarization measurements in early optical afterglows.

Abstract

Jet precessions are widely involved in astrophysical phenomena from galaxies to X-ray binaries and gamma-ray bursts (GRBs). Polarization presents a unique probe of the magnetic fields in GRB jets. The precession of GRBs relativistic jets will change the geometry within the observable emitting region of the jet, which can potentially affect the polarization of the afterglow. In this paper, we take into account jet precession to study the polarization evolution and corresponding light curves in GRB early optical afterglows with ordered and random magnetic field geometries. We find that the jet precession in long-lived engines can significantly reduce the polarization degree (PD) regardless of the magnetic field structure. The strongest PD attenuation is found when the line of sight is aligned with the precession axis. Our results show that jet precession can provide new insight into the low PD measured in the early optical afterglows of GRBs.