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Polarization properties of photospheric emission from relativistic, collimated outflows
KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.ORCID iD: 0000-0002-0642-1055
KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.ORCID iD: 0000-0002-9769-8016
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
Abstract [en]

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.
Keyword [en]
Gamma-ray burst: general, Polarization, Radiation mechanisms: thermal, Radiative transfer, Scattering
National Category
Physical Sciences
URN: urn:nbn:se:kth:diva-146938DOI: 10.1093/mnras/stu457ISI: 000336213800031ScopusID: 2-s2.0-84899881224OAI: diva2:727914

QC 20140623

Available from: 2014-06-23 Created: 2014-06-18 Last updated: 2014-06-23Bibliographically approved

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Lundman, ChristofferRyde, Felix
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