Origin of the Twice-90° Rotations of the Polarization Angle in GRB 170114A and GRB 160821A

• Published in: The Astrophysical journal Vol. 972; no. 1; pp. 15 - 24
• Main Authors: Wang, Xu, Lan, Mi-Xiang, Tang, Qing-Wen, Wu, Xue-Feng, Dai, Zi-Gao
• Format: Journal Article
• Language: English
• Published: Philadelphia The American Astronomical Society 01.09.2024; IOP Publishing
• Subjects: Black holes; Gamma ray bursts; Gamma rays; Light curve; Magnetars; Magnetic field configurations; Magnetic fields; Polarization; Spectral emittance; Starlight polarization
• ISSN: 0004-637X; 1538-4357
• DOI: 10.3847/1538-4357/ad5be8

The observed abrupt twice-90° rotations of the polarization angle (PA) in the prompt phase of gamma-ray bursts (GRBs) are difficult to understand within the current one-emitting-shell models. Here, we apply a model with multiple emitting shells to solve this new challenging problem. Two configurations of large-scale ordered magnetic fields in the shells are considered: toroidal and aligned. Together with the light curves and the spectral peak energy evolutions, the twice-90° PA rotations in GRB 170114A and GRB 160821A could be well interpreted with the multishell aligned magnetic field configuration (MFC). Our numerical calculations also show that the multiple shells with the toroidal MFC could not explain the observed twice-90° PA rotations. An aligned MFC in the GRB outflow usually indicates the preference of a magnetar central engine, while a toroidal field configuration is typically related to a central black hole. Therefore, the magnetar central engines for the two GRBs are favored.