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Title: WEIBEL INSTABILITY DRIVEN BY SPATIALLY ANISOTROPIC DENSITY STRUCTURES

Abstract

Observations of afterglows of gamma-ray bursts (GRBs) suggest that post-shock magnetic fields are strongly amplified to about 100 times the shock-compressed value. The Weibel instability appears to play an important role in generating the magnetic field. However, recent simulations of collisionless shocks in homogeneous plasmas show that the magnetic field generated by the Weibel instability rapidly decays. There must be some density fluctuations in interstellar and circumstellar media. The density fluctuations are anisotropically compressed in the downstream region of relativistic shocks. In this paper, we study the Weibel instability in electron–positron plasmas with spatially anisotropic density distributions by means of two-dimensional particle-in-cell simulations. We find that large magnetic fields are maintained for a longer time by the Weibel instability driven by spatially anisotropic density structure. Particles anisotropically escape from the high density region, so that a temperature anisotropy is generated and the Weibel instability becomes unstable. Our simulation results suggest that the Weibel instability driven by an anisotropic density structure can generate sufficiently large magnetic fields and they can cover sufficiently large regions to explain the afterglow emission of GRBs.

Authors:
;  [1]
  1. Department of Physics and Mathematics, Aoyama Gakuin University, 5-10-1 Fuchinobe, Sagamihara 252-5258 (Japan)
Publication Date:
OSTI Identifier:
22666103
Resource Type:
Journal Article
Journal Name:
Astrophysical Journal
Additional Journal Information:
Journal Volume: 825; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA); Journal ID: ISSN 0004-637X
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; AFTERGLOW; ANISOTROPY; COSMIC GAMMA BURSTS; DENSITY; DISTRIBUTION; EMISSION; FLUCTUATIONS; GAMMA RADIATION; HOMOGENEOUS PLASMA; INSTABILITY; MAGNETIC FIELDS; POSITRONS; RELATIVISTIC RANGE; SHOCK WAVES; SIMULATION; TWO-DIMENSIONAL CALCULATIONS

Citation Formats

Tomita, Sara, and Ohira, Yutaka, E-mail: tomisara@phys.aoyama.ac.jp. WEIBEL INSTABILITY DRIVEN BY SPATIALLY ANISOTROPIC DENSITY STRUCTURES. United States: N. p., 2016. Web. doi:10.3847/0004-637X/825/2/103.
Tomita, Sara, & Ohira, Yutaka, E-mail: tomisara@phys.aoyama.ac.jp. WEIBEL INSTABILITY DRIVEN BY SPATIALLY ANISOTROPIC DENSITY STRUCTURES. United States. doi:10.3847/0004-637X/825/2/103.
Tomita, Sara, and Ohira, Yutaka, E-mail: tomisara@phys.aoyama.ac.jp. Sun . "WEIBEL INSTABILITY DRIVEN BY SPATIALLY ANISOTROPIC DENSITY STRUCTURES". United States. doi:10.3847/0004-637X/825/2/103.
@article{osti_22666103,
title = {WEIBEL INSTABILITY DRIVEN BY SPATIALLY ANISOTROPIC DENSITY STRUCTURES},
author = {Tomita, Sara and Ohira, Yutaka, E-mail: tomisara@phys.aoyama.ac.jp},
abstractNote = {Observations of afterglows of gamma-ray bursts (GRBs) suggest that post-shock magnetic fields are strongly amplified to about 100 times the shock-compressed value. The Weibel instability appears to play an important role in generating the magnetic field. However, recent simulations of collisionless shocks in homogeneous plasmas show that the magnetic field generated by the Weibel instability rapidly decays. There must be some density fluctuations in interstellar and circumstellar media. The density fluctuations are anisotropically compressed in the downstream region of relativistic shocks. In this paper, we study the Weibel instability in electron–positron plasmas with spatially anisotropic density distributions by means of two-dimensional particle-in-cell simulations. We find that large magnetic fields are maintained for a longer time by the Weibel instability driven by spatially anisotropic density structure. Particles anisotropically escape from the high density region, so that a temperature anisotropy is generated and the Weibel instability becomes unstable. Our simulation results suggest that the Weibel instability driven by an anisotropic density structure can generate sufficiently large magnetic fields and they can cover sufficiently large regions to explain the afterglow emission of GRBs.},
doi = {10.3847/0004-637X/825/2/103},
journal = {Astrophysical Journal},
issn = {0004-637X},
number = 2,
volume = 825,
place = {United States},
year = {2016},
month = {7}
}