Faraday rotation and physical conditions in the Crab Nebula

New, high-resolution radio images of the Crab Nebula at four frequencies are presented. These are used to construct reliable depolarization and rotation measure (RM) maps. The polarization maps show considerable small-scale structure. The features in the RM map appear unrelated to any structure visi...

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Bibliographic Details
Published inThe Astrophysical journal Vol. 368; no. 1; pp. 231 - 240
Main Authors BIETENHOLZ, M. F, KRONBERG, P. P
Format Journal Article
LanguageEnglish
Published Chicago, IL University of Chicago Press 01.02.1991
Subjects
640102 - Astrophysics & Cosmology- Stars & Quasi-Stellar, Radio & X-Ray Sources
Astronomy
BREMSSTRAHLUNG
CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS
COSMIC RADIO SOURCES
CRAB NEBULA
Earth, ocean, space
ELECTROMAGNETIC RADIATION
Exact sciences and technology
FARADAY EFFECT
Interstellar medium (ism) and nebulae in milky way
MAGNETIC FIELDS
MORPHOLOGY
NEBULAE
POLARIZATION
PULSARS
RADIATIONS
RADIOWAVE RADIATION
STELLAR ACTIVITY
STELLAR RADIATION
Stellar systems. Galactic and extragalactic objects and systems. The universe
STELLAR WINDS
SUPERNOVA REMNANTS
SYNCHROTRON RADIATION
Depolarization
Polarization
Radiation mechanism
Crab nebula
VLA observation
Faraday effect
Data table
Radio interferometric observation
Rotation measure
Magnetic field
Supernova remnant
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Summary:New, high-resolution radio images of the Crab Nebula at four frequencies are presented. These are used to construct reliable depolarization and rotation measure (RM) maps. The polarization maps show considerable small-scale structure. The features in the RM map appear unrelated to any structure visible in the total intensity. The large-scale RM is remarkably constant at about -21 rad/sq m across the nebula, and is mostly external, with at most a small contribution from the nebula itself. The synchrotron-emitting regions are quite separate from those in which most of the Faraday rotation occurs. In the former, the scale size of the magnetic field structure is about 0.1 pc and the (thermal) densities are low. It is shown that the radio depolarization must be caused by a network of Faraday rotating filaments containing thermal material. Most of these filaments are too small to be seen individually, have a filling factor of about 0.3, and RMs of a few hundred radians per square meter. 28 refs.
ISSN:0004-637X
1538-4357
DOI:10.1086/169686