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Title: COSMIC RAY DIFFUSION FRONTS IN THE VIRGO CLUSTER

Abstract

The pair of large radio lobes in the Virgo cluster, each about 23 kpc in radius, have curiously sharp outer edges where the radio-synchrotron continuum flux declines abruptly. However, just adjacent to this sharp transition, the radio flux increases. This radio limb-brightening is observed over at least half of the perimeter of both lobes. We describe slowly propagating steady-state diffusion fronts that explain these counterintuitive features. Because of the natural buoyancy of radio lobes, the magnetic field is largely tangent to the lobe boundary, an alignment that polarizes the radio emission and dramatically reduces the diffusion coefficient of relativistic electrons. As cosmic ray electrons diffuse slowly into the cluster gas, the local magnetic field and gas density are reduced as gas flows back toward the radio lobe. Radio emission peaks can occur because the synchrotron emissivity increases with magnetic field and then decreases with the density of non-thermal electrons. A detailed comparison of steady diffusion fronts with quantitative radio observations may reveal information about the spatial variation of magnetic fields and the diffusion coefficient of relativistic electrons. On larger scales, some reduction of the gas density inside the Virgo lobes due to cosmic ray pressure must occur and may bemore » measurable. Such X-ray observations could reveal important information about the presence of otherwise unobservable non-thermal components such as relativistic electrons of low energy or proton cosmic rays.« less

Authors:
;  [1]
  1. Department of Astronomy and Astrophysics, University of California Observatories/Lick Observatory, University of California, Santa Cruz, CA 95064 (United States)
Publication Date:
OSTI Identifier:
21578360
Resource Type:
Journal Article
Journal Name:
Astrophysical Journal
Additional Journal Information:
Journal Volume: 736; Journal Issue: 1; Other Information: DOI: 10.1088/0004-637X/736/1/6; Journal ID: ISSN 0004-637X
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; COSMIC RADIATION; DENSITY; DIFFUSION; ELECTRONS; EMISSION; GALAXY CLUSTERS; MAGNETIC FIELDS; RADIATION PRESSURE; RADIOWAVE RADIATION; X-RAY GALAXIES; COSMIC RAY SOURCES; COSMIC X-RAY SOURCES; ELECTROMAGNETIC RADIATION; ELEMENTARY PARTICLES; FERMIONS; GALAXIES; IONIZING RADIATIONS; LEPTONS; PHYSICAL PROPERTIES; RADIATIONS

Citation Formats

Mathews, William G., and Guo Fulai, E-mail: mathews@ucolick.org. COSMIC RAY DIFFUSION FRONTS IN THE VIRGO CLUSTER. United States: N. p., 2011. Web. doi:10.1088/0004-637X/736/1/6.
Mathews, William G., & Guo Fulai, E-mail: mathews@ucolick.org. COSMIC RAY DIFFUSION FRONTS IN THE VIRGO CLUSTER. United States. doi:10.1088/0004-637X/736/1/6.
Mathews, William G., and Guo Fulai, E-mail: mathews@ucolick.org. Wed . "COSMIC RAY DIFFUSION FRONTS IN THE VIRGO CLUSTER". United States. doi:10.1088/0004-637X/736/1/6.
@article{osti_21578360,
title = {COSMIC RAY DIFFUSION FRONTS IN THE VIRGO CLUSTER},
author = {Mathews, William G. and Guo Fulai, E-mail: mathews@ucolick.org},
abstractNote = {The pair of large radio lobes in the Virgo cluster, each about 23 kpc in radius, have curiously sharp outer edges where the radio-synchrotron continuum flux declines abruptly. However, just adjacent to this sharp transition, the radio flux increases. This radio limb-brightening is observed over at least half of the perimeter of both lobes. We describe slowly propagating steady-state diffusion fronts that explain these counterintuitive features. Because of the natural buoyancy of radio lobes, the magnetic field is largely tangent to the lobe boundary, an alignment that polarizes the radio emission and dramatically reduces the diffusion coefficient of relativistic electrons. As cosmic ray electrons diffuse slowly into the cluster gas, the local magnetic field and gas density are reduced as gas flows back toward the radio lobe. Radio emission peaks can occur because the synchrotron emissivity increases with magnetic field and then decreases with the density of non-thermal electrons. A detailed comparison of steady diffusion fronts with quantitative radio observations may reveal information about the spatial variation of magnetic fields and the diffusion coefficient of relativistic electrons. On larger scales, some reduction of the gas density inside the Virgo lobes due to cosmic ray pressure must occur and may be measurable. Such X-ray observations could reveal important information about the presence of otherwise unobservable non-thermal components such as relativistic electrons of low energy or proton cosmic rays.},
doi = {10.1088/0004-637X/736/1/6},
journal = {Astrophysical Journal},
issn = {0004-637X},
number = 1,
volume = 736,
place = {United States},
year = {2011},
month = {7}
}