Probing the Efficiency of Electron-Proton Coupling in Relativistic Collisionless Shocks through the Radio Polarimetry of Gamma-Ray Burst Afterglows

Kenji Toma, Kunihito Ioka, Takashi Nakamura

Research output: Chapter in Book/Report/Conference proceedingConference contribution

Abstract

The late-time optical/radio afterglows of γ-ray bursts (GRBs) are believed to be synchrotron emission of electrons accelerated in relativistic collisionless shocks propagating in the ambient medium of the sources. However, the fraction f of electrons that are coupled to protons and accelerated remains unclear and a large number of thermal electrons that are not coupled to protons may be left behind. If f<1, the true explosion energies of GRBs are f -1 times larger than those commonly estimated with f=1. Thus the value of f gives an important constraint on the nature of the central engine of GRBs and the physics of collisionless shocks. Although early-time radio observations can probe the thermal electrons, they are difficult at present. We show that the Faraday rotation effects of the thermal electrons may suppress the linear polarization of the afterglow at frequencies higher than the absorption frequency in the late time, if the magnetic field is ordered at least in parts, and that f can be constrained through the observation of the effects. We find that those effects may be detected with late-time, ≥1 day, polarimetry with ALMA for a burst occurring within 1 Gpc (i.e., z≃0.2), if f∼10 -1.

Original languageEnglish
Title of host publicationGamma-Ray Bursts 2007 - Proceedings of the Santa Fe Conference
Pages472-475
Number of pages4
DOIs
Publication statusPublished - 2008 Dec 1
Externally publishedYes
EventSanta Fe Conference on Gamma-Ray Bursts 2007, GRB 2007 - Santa Fe, NM, United States
Duration: 2007 Nov 52007 Nov 9

Publication series

NameAIP Conference Proceedings
Volume1000
ISSN (Print)0094-243X
ISSN (Electronic)1551-7616

Conference

ConferenceSanta Fe Conference on Gamma-Ray Bursts 2007, GRB 2007
CountryUnited States
CitySanta Fe, NM
Period07/11/507/11/9

Keywords

  • γ-ray bursts1
  • γ-ray sources

ASJC Scopus subject areas

  • Ecology, Evolution, Behavior and Systematics
  • Ecology
  • Plant Science
  • Physics and Astronomy(all)
  • Nature and Landscape Conservation

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