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Title: TURBULENT COSMIC-RAY REACCELERATION AT RADIO RELICS AND HALOS IN CLUSTERS OF GALAXIES

Abstract

Radio relics are synchrotron emission found on the periphery of galaxy clusters. From the position and the morphology, it is often believed that the relics are generated by cosmic-ray (CR) electrons accelerated at shocks through a diffusive shock acceleration (DSA) mechanism. However, some radio relics have harder spectra than the prediction of the standard DSA model. One example is observed in the cluster 1RXS J0603.3+4214, which is often called the “Toothbrush Cluster.” Interestingly, the position of the relic is shifted from that of a possible shock. In this study, we show that these discrepancies in the spectrum and the position can be solved if turbulent (re)acceleration is very effective behind the shock. This means that for some relics turbulent reacceleration may be the main mechanism to produce high-energy electrons, contrary to the common belief that it is the DSA. Moreover, we show that for efficient reacceleration, the effective mean free path of the electrons has to be much smaller than their Coulomb mean free path. We also study the merging cluster 1E 0657−56, or the “Bullet Cluster,” in which a radio relic has not been found at the position of the prominent shock ahead of the bullet. We indicate that amore » possible relic at the shock is obscured by the observed large radio halo that is generated by strong turbulence behind the shock. We propose a simple explanation of the morphological differences of radio emission among the Toothbrush, the Bullet, and the Sausage (CIZA J2242.8+5301) Clusters.« less

Authors:
 [1];  [2];  [3];  [4];  [5]
  1. Department of Earth and Space Science, Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043 (Japan)
  2. Department of Physics, Yamagata University, 1-4-12 Kojirakawa-machi, Yamagata 990-8560 (Japan)
  3. Department of Physics and Mathematics, Aoyama Gakuin University, Fuchinobe, Chuou-ku, Sagamihara 252-5258 (Japan)
  4. SRON Netherlands Institute for Space Research, Sorbonnelaan 2, 3584 CA Utrecht (Netherlands)
  5. Tohoku Bunkyo College, 515 Katayachi, Yamagata 990-2316 (Japan)
Publication Date:
OSTI Identifier:
22521756
Resource Type:
Journal Article
Journal Name:
Astrophysical Journal
Additional Journal Information:
Journal Volume: 815; 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; ACCELERATION; COSMIC ELECTRONS; GALAXIES; GALAXY CLUSTERS; MEAN FREE PATH; MORPHOLOGY; PHOTON EMISSION; SHOCK WAVES; SYNCHROTRON RADIATION; TURBULENCE

Citation Formats

Fujita, Yutaka, Takizawa, Motokazu, Yamazaki, Ryo, Akamatsu, Hiroki, and Ohno, Hiroshi, E-mail: fujita@vega.ess.sci.osaka-u.ac.jp. TURBULENT COSMIC-RAY REACCELERATION AT RADIO RELICS AND HALOS IN CLUSTERS OF GALAXIES. United States: N. p., 2015. Web. doi:10.1088/0004-637X/815/2/116.
Fujita, Yutaka, Takizawa, Motokazu, Yamazaki, Ryo, Akamatsu, Hiroki, & Ohno, Hiroshi, E-mail: fujita@vega.ess.sci.osaka-u.ac.jp. TURBULENT COSMIC-RAY REACCELERATION AT RADIO RELICS AND HALOS IN CLUSTERS OF GALAXIES. United States. doi:10.1088/0004-637X/815/2/116.
Fujita, Yutaka, Takizawa, Motokazu, Yamazaki, Ryo, Akamatsu, Hiroki, and Ohno, Hiroshi, E-mail: fujita@vega.ess.sci.osaka-u.ac.jp. Sun . "TURBULENT COSMIC-RAY REACCELERATION AT RADIO RELICS AND HALOS IN CLUSTERS OF GALAXIES". United States. doi:10.1088/0004-637X/815/2/116.
@article{osti_22521756,
title = {TURBULENT COSMIC-RAY REACCELERATION AT RADIO RELICS AND HALOS IN CLUSTERS OF GALAXIES},
author = {Fujita, Yutaka and Takizawa, Motokazu and Yamazaki, Ryo and Akamatsu, Hiroki and Ohno, Hiroshi, E-mail: fujita@vega.ess.sci.osaka-u.ac.jp},
abstractNote = {Radio relics are synchrotron emission found on the periphery of galaxy clusters. From the position and the morphology, it is often believed that the relics are generated by cosmic-ray (CR) electrons accelerated at shocks through a diffusive shock acceleration (DSA) mechanism. However, some radio relics have harder spectra than the prediction of the standard DSA model. One example is observed in the cluster 1RXS J0603.3+4214, which is often called the “Toothbrush Cluster.” Interestingly, the position of the relic is shifted from that of a possible shock. In this study, we show that these discrepancies in the spectrum and the position can be solved if turbulent (re)acceleration is very effective behind the shock. This means that for some relics turbulent reacceleration may be the main mechanism to produce high-energy electrons, contrary to the common belief that it is the DSA. Moreover, we show that for efficient reacceleration, the effective mean free path of the electrons has to be much smaller than their Coulomb mean free path. We also study the merging cluster 1E 0657−56, or the “Bullet Cluster,” in which a radio relic has not been found at the position of the prominent shock ahead of the bullet. We indicate that a possible relic at the shock is obscured by the observed large radio halo that is generated by strong turbulence behind the shock. We propose a simple explanation of the morphological differences of radio emission among the Toothbrush, the Bullet, and the Sausage (CIZA J2242.8+5301) Clusters.},
doi = {10.1088/0004-637X/815/2/116},
journal = {Astrophysical Journal},
issn = {0004-637X},
number = 2,
volume = 815,
place = {United States},
year = {2015},
month = {12}
}