Polarization properties of photospheric emission from relativistic, collimated outflows
2014 (English)In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 440, no 4, 3292-3308 p.Article in journal (Refereed) Published
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.
Place, publisher, year, edition, pages
2014. Vol. 440, no 4, 3292-3308 p.
Gamma-ray burst: general, Polarization, Radiation mechanisms: thermal, Radiative transfer, Scattering
IdentifiersURN: urn:nbn:se:kth:diva-146938DOI: 10.1093/mnras/stu457ISI: 000336213800031ScopusID: 2-s2.0-84899881224OAI: oai:DiVA.org:kth-146938DiVA: diva2:727914
QC 201406232014-06-232014-06-182014-06-23Bibliographically approved