Numerical modeling of radio emission from young supernova remnants
Jun, Byung-Il
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https://hdl.handle.net/2142/23322
Description
Title
Numerical modeling of radio emission from young supernova remnants
Author(s)
Jun, Byung-Il
Issue Date
1995
Doctoral Committee Chair(s)
Norman, Michael L.
Department of Study
Astronomy
Discipline
Astronomy
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Physics, Astronomy and Astrophysics
Language
eng
Abstract
Young supernova remnants such as Tycho, Kepler, and Cas A generally show a circular, clumpy shell near the outer boundary in both radio and X-ray emission. The magnetic field in the radio shell has been inferred to be in the range of $10\sp{-4}\sim10\sp{-3}G$ by the minimum energy requirements. The detailed polarization studies reveal that the magnetic field in the shell exhibits a cellular pattern with a net radial orientation. In this thesis, attempts are made to explain the mechanism for the origin of strong radio emission from young supernova remnants by modeling the interaction between the ejecta and the interstellar medium.
"The Rayleigh-Taylor instability near the contact interface between the ejecta and the shocked ambient medium is studied in great detail by means of two- and three-dimensional MHD simulations. It is shown that the Rayleigh-Taylor instability model produce the thick clumpy radio shell as well as clumpy X-ray shell. The amplified magnetic field due to the Rayleigh-Taylor and Kelvin-Helmholtz instabilities is indeed strong and radial although the field strength is sensitive to the numerical resolution. However, the polarized magnetic field from the simulation is found to be dependent on the viewing angle because of the undisturbed large scale magnetic fields near the outer shock. To reconcile this result, the magnetic field in an ambient medium is required to be disordered on large scale, or an extra mechanism is required to randomize the large scale field if the ambient magnetic fields are ordered on a few parsec scale. The high degree of fractional polarization with a radial direction of magnetic fields in ""rims"" of Tycho's supernova remnant cannot be solved by the Rayleigh-Taylor instability model."
In order to attack the unsolved problems by the Rayleigh-Taylor instability model, an assumption of uniform medium is relaxed to investigate the effect of cloudy medium. The cloudy medium model is found to produce the dominant radial magnetic fields in the mixing region overall with a larger fractional polarization near the outer shock. The total intensity is found to be strongly correlated with the polarized intensity which implies that the ordered magnetic fields are more responsible for the radio emission. The radio luminosity is significantly enhanced by the clouds encounter while the effect on X-ray luminosity is less significant. This model is a strong candidate for the mechanism which is responsible for the origin of many radio features in young supernova remnants.
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