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Polarization of Prompt Gamma‐Ray Burst Emission: Evidence for Electromagnetically Dominated Outflow

Lyutikov, M. and Pariev, V. I. and Blandford, R. D. (2003) Polarization of Prompt Gamma‐Ray Burst Emission: Evidence for Electromagnetically Dominated Outflow. Astrophysical Journal, 597 (2). pp. 998-1009. ISSN 0004-637X. https://resolver.caltech.edu/CaltechAUTHORS:20190604-101747085

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Abstract

Observations by the RHESSI satellite of the large polarization of the prompt γ-ray emission from γ-ray burst (GRB) 021206 imply that the magnetic field coherence scale is larger than the size of the visible emitting region, ~R/Γ, where R is the radius of the flow and Γ is the associated Lorentz factor. Such fields cannot be generated in a causally disconnected, hydrodynamically dominated outflow. Electromagnetic models of GRBs, in which large-scale, dynamically dominant, magnetic fields are present in the outflow from the very beginning, provide a natural explanation of this large reported linear polarization. We derive the Stokes parameters of the synchrotron emission of a relativistically moving plasma with a given magnetic field configuration and calculate the pulse-averaged polarization fraction of the emission from a relativistically expanding shell carrying a global toroidal magnetic field. For viewing angles larger than 1/Γ, the observed patch of the emitting shell has an almost homogeneous magnetic field, producing a large fractional polarization (56% for a power-law energy distribution of relativistic particles, dn/dϵ ∝ ϵ^(-3)). The maximum polarization is smaller than the theoretical upper limit for a stationary plasma in a uniform magnetic field because of relativistic kinematic effects.


Item Type:Article
Related URLs:
URLURL TypeDescription
https://doi.org/10.1086/378497DOIArticle
https://arxiv.org/abs/astro-ph/0305410arXivDiscussion Paper
ORCID:
AuthorORCID
Blandford, R. D.0000-0002-1854-5506
Alternate Title:Polarization of prompt GRB emission: evidence for electromagnetically-dominated outflow
Additional Information:© 2003 The American Astronomical Society. Received 2003 May 21; accepted 2003 July 17. V. P. acknowledges support from Department of Energy grant DE-FG02-00ER54600.
Group:TAPIR
Funders:
Funding AgencyGrant Number
Department of Energy (DOE)DE-FG02-00ER54600
Subject Keywords:gamma rays: bursts — MHD — polarization
Issue or Number:2
Record Number:CaltechAUTHORS:20190604-101747085
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20190604-101747085
Official Citation:M. Lyutikov et al 2003 ApJ 597 998
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:96105
Collection:CaltechAUTHORS
Deposited By: Tony Diaz
Deposited On:04 Jun 2019 18:06
Last Modified:03 Oct 2019 21:19

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