Polarization degree of magnetic field structure changes caused by random magnetic field in Gamma-ray Burst

TL;DR

This study models how random magnetic fields influence polarization degrees in gamma-ray burst jets, revealing significant effects on polarization measurements across energy ranges and introducing polarization angle rotations.

Contribution

It presents a novel model combining ordered and random magnetic fields to analyze polarization evolution in gamma-ray bursts, highlighting the impact of magnetic disorder.

Findings

Random magnetic fields reduce low-energy X-ray polarization degrees.

Polarization angle rotations occur earlier in high-energy segments.

Polarization degrees are similar across energy ranges when randomness is considered.

Abstract

In a Poynting-flux-dominated (PFD) jet that exhibits an ordered magnetic field, a transition towards turbulence and magnetic disorder follows after magnetic reconnection and energy dissipation during the prompt emission phase. In this process, the configuration of the magnetic field evolves with time, rendering it impossible to entirely categorize the magnetic field as ordered. Therefore, we assumed a crude model that incorporates a random magnetic field and an ordered magnetic field, and takes into account the proportionality of the random magnetic field strength to the ordered magnetic field, in order to compute the polarization degree (PD) curve for an individual pulse. It has been discovered that the random magnetic field has a significant impact on the PD results of the low-energy X-ray. In an ordered magnetic field, the X-ray segment maintains a significant PD compared to those in the hundreds of keV and MeV ranges even after electron injection ceases, this making PD easier to detect by polarimetry. However, when the random magnetic field is introduced, the low-energy and high-energy PDs exhibit a similar trend, with the X-ray PD being lower than that of the high-energy segment. Of course, this is related to the rate of disorder in the magnetic field. Additionally, there is two rotation of the polarization angles (PAs) that were not present previously, and the rotation of the PA in the high-energy segment occurs slightly earlier. These results are unrelated to the structure of the ordered magnetic field.