Rotation of Polarization Angle in Gamma-Ray Burst Prompt Phase. II. The Influence of the Parameters

• Published in: The Astrophysical journal 2024-09, Vol.973 (1), p.2
• Main Authors: Li, Jia-Sheng, Wang, Hao-Bing, Lan, Mi-Xiang
• Format: Article
• Language: English
• Subjects: Depolarization; Energy spectra; Flux density; Gamma ray bursts; Gamma rays; Light curve; Lorentz factor; Magnetic fields; Magnetic properties; Magnetic reconnection; Parameters; Physical properties; Polarization; Rotation
• ISSN: 0004-637X; 1538-4357
• DOI: 10.3847/1538-4357/ad6f99

In addition to the light curve and energy spectrum, polarization is also important for inferring the physical properties of the gamma-ray burst (GRB). Rotation of the polarization angle (PA) with time will cause depolarization of the time-integrated polarization degree. However, it has rarely been studied before. Here, we use a magnetic reconnection model with a large-scale ordered aligned magnetic field in the emitting region to study the influence of the parameters on the PA rotations in the GRB prompt phase. We find that the half-opening angle of the jet θ j , the observational angle θ V , and the bulk Lorentz factor Γ all have significant impacts on the PA rotations. The PA rotations are affected by the product value of θ j Γ 0 (Γ 0 is the normalization factor of Γ with Γ ( r ) = Γ 0 ( r / r 0 ) s ), but are roughly independent of the concrete values of both θ j and Γ 0 . For the typical parameters, the changes of the PA within T 90 (△PA) would be within (12°, 66°) for slight off-axis observations, where T 90 is the duration of the burst with the accumulated flux density ranging from 5% to 95%. The q range for △PA > 10° becomes smaller with the increase of the product value of θ j Γ 0 . The most significant PA rotation with △PA ∼ 90° will happen when θ j Γ 0 > 50 and 1.0 < q ≤ 1.2.