2015/09/08 by Lara Nava, Nava, Lara, Ehud Nakar +3
Physics and Astronomy · #Astrophysics and Cosmic Phenomena #FOS: Physical sciences #Gamma-ray bursts and supernovae #High Energy Astrophysical Phenomena (astro-ph.HE) #Solar and Space Plasma Dynamics
paper · pdf · doi:10.48550/arxiv.1509.02525
openalex publication_date 2015/09/08 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28
Polarization measurements from relativistic outflows are a valuable tool to\nprobe the geometry of the emission region and the microphysics of the particle\ndistribution. Indeed, the polarization level depends on: (i) the local magnetic\nfield orientation, (ii) the geometry of the emitting region with respect to the\nline of sight, and (iii) the electron pitch-angle distribution. Here we\nconsider optically thin synchrotron emission and we extend the theory of\ncircular polarization from a point source to an extended radially expanding\nrelativistic jet. We present numerical estimates for both linear and circular\npolarization in such systems. We consider different configurations of the\nmagnetic field, spherical and jetted outflows, isotropic and anisotropic\npitch-angle distributions, and outline the difficulty in obtaining the reported\nhigh level of circular polarization observed in the afterglow of GRB 121024A.\nWe conclude that the origin of the observed polarization cannot be intrinsic to\nan optically thin synchrotron process, even when the electron pitch-angle\ndistribution is extremely anisotropic.\n