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Polarization of Gamma-Ray Bursts in the Dissipative Photosphere Model
KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics. Columbia Univ.ORCID iD: 0000-0002-0642-1055
Columbia Univ, Phys Dept, 538 West 120th St, New York, NY 10027 USA.;Columbia Univ, Columbia Astrophys Lab, 538 West 120th St, New York, NY 10027 USA.;Tartu Observ, EE-61602 Toravere, Tartumaa, Estonia..
Columbia Univ, Phys Dept, 538 West 120th St, New York, NY 10027 USA.;Columbia Univ, Columbia Astrophys Lab, 538 West 120th St, New York, NY 10027 USA..
2018 (English)In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 856, no 2, article id 145Article in journal (Refereed) Published
Abstract [en]

The MeV spectral peak of gamma-ray bursts (GRBs) is best explained as photospheric emission from a dissipative relativistic jet. The observed non-blackbody spectrum shows that sub-photospheric dissipation involves both thermal plasma heating and injection of nonthermal particles, which quickly cool through inverse Compton scattering and emission of synchrotron radiation. Synchrotron photons emitted around and above the photosphere are predicted to dominate the low-energy part of the GRB spectrum, starting from roughly a decade in energy below the MeV peak. We show that this leads to a unique polarization signature: a rise in GRB polarization toward lower energies. We compute the polarization degree of GRB radiation as a function of photon energy for a generic jet model, and show the predictions for GRBs 990123, 090902B, and 110721A. The expected polarization is significant in the X-ray band, in particular for bursts similar to GRB 090902B. The model predicts that radiation in the MeV peak (and at higher energies) is unpolarized as long as the jet is approximately uniform on angular scales delta theta greater than or similar to Gamma(-1) where G is the bulk Lorentz factor of the jet.

Place, publisher, year, edition, pages
IOP PUBLISHING LTD , 2018. Vol. 856, no 2, article id 145
Keywords [en]
gamma-ray burst: general, polarization, radiation mechanisms: non-thermal, radiative transfer, relativistic processes, scattering
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
URN: urn:nbn:se:kth:diva-228140DOI: 10.3847/1538-4357/aab3e8ISI: 000429119800004Scopus ID: 2-s2.0-85045537662OAI: oai:DiVA.org:kth-228140DiVA, id: diva2:1207097
Note

QC 20180518

Available from: 2018-05-18 Created: 2018-05-18 Last updated: 2018-05-18Bibliographically approved

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Lundman, Christoffer

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