2013/09/29 by Christoffer Lundman, Asaf Pe’er, Asaf Pe'er +2 · 67 citations
Physics and Astronomy · #Astronomy #Astrophysics #Astrophysics and Cosmic Phenomena #Brewster's angle #Degree of polarization #Gamma-ray bursts and supernovae #Laser #Linear polarization #Lorentz factor #Lorentz transformation #Optics #Photon #Physics #Polarization (electrochemistry) #Pulsars and Gravitational Waves Research #Quantum mechanics #Radiative transfer #Scattering #Spectral index #Spectral line #Viewing angle #astro-ph.HE
paper · pdf · doi:10.1093/mnras/stu457
published in Monthly Notices of the Royal Astronomical Society 440(4), 3292-3308 (Oxford University Press) · 17 pages, 12 figures, submitted to MNRAS
arxiv created 2013/09/29 · openalex publication_date 2014/04/17 · arxiv updated 2015/06/17 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/05
We consider the polarization properties of photospheric emission originating in jets consisting of a highly relativistic core of opening angle θj and Lorentz factor Γ0, and a surrounding shear layer where the Lorentz factor is decreasing as a power law of index p with angle from the jet axis. We find significant degrees of linear polarization for observers located at viewing angles θv ≳ θj. In particular, the polarization degree of emission from narrow jets (θj ≈ 1/Γ0) with steep Lorentz factor gradients (p ≳ 4) reaches ∼40 per cent. The angle of polarization may shift by π/2 for time-variable jets. The spectrum below the thermal peak of the polarized emission appears non-thermal due to aberration of light, without the need for additional radiative processes or energy dissipation. Furthermore, above the thermal peak a power law of photons forms due to Comptonization of photons that repeatedly scatter between regions of different Lorentz factor before escaping. We show that polarization degrees of a few tens of per cent and broken power-law spectra are natural in the context of photospheric emission from structured jets. Applying the model to gamma-ray bursts, we discuss expected correlations between the spectral shape and the polarization degree of the prompt emission.