Temporal evolution of depolarization and magnetic field of FRB 20201124A

TL;DR

This study investigates the temporal changes in depolarization and magnetic fields of FRB 20201124A, revealing their correlation and suggesting a complex magneto-ionized environment influenced by a massive star's wind and disk.

Contribution

It provides the first detailed analysis of the time evolution of depolarization and magnetic fields in a repeating FRB using simultaneous measurements.

Findings

Depolarization and magnetic field strength vary over time.

Evolution of depolarization correlates with rotation measure changes.

Magneto-ionized environment likely shaped by a massive star's wind and disk.

Abstract

Fast radio bursts (FRBs) are energetic millisecond phenomena in radio band. Polarimetric studies of repeating FRBs indicate that many of these sources occupy extreme and complex magneto-ionized environments. Recently, a frequency-dependent depolarization has been discovered in several repeating FRBs. However, the temporal evolution of polarization properties is limited by the burst rate and observational cadence of telescopes. In this letter, the temporal evolution of depolarization in repeating FRB 20201124A is explored. Using the simultaneous variation of rotation measure and dispersion measure, we also measure the strength of a magnetic field parallel to the line-of-sight. The strength ranges from a few $\mu {\rm G}$ to $10^3\ \mu {\rm G}$. In addition, we find that the evolution of depolarization and magnetic field traces the evolution of rotation measure. Our result supports that the variation of depolarization, rotation measure and the magnetic field are determined by the same complex magneto-ionized screen surrounding the FRB source. The derived properties of the screen are consistent with the wind and the decretion disk of a massive star.