Propagation of radiation in astrophysical media: Gravitational lenses and astrophysical masers
Scappaticci, Gerardo Angelo
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https://hdl.handle.net/2142/21822
Description
Title
Propagation of radiation in astrophysical media: Gravitational lenses and astrophysical masers
Author(s)
Scappaticci, Gerardo Angelo
Issue Date
1992
Doctoral Committee Chair(s)
Watson, W.D.
Department of Study
Physics
Discipline
Physics
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
In Part I the time variability of the radiation emitted by astrophysical masers is studied by numerically solving the system of time dependent non-linear partial differential equations of radiative transfer through a masing gas. The calculations demonstrate for the first time how oscillations, with periods which are comparable to the light travel time through the maser, might develop as a result of radiative instabilities. In addition, we perform a linear stability analysis of the radiative transfer equations and the rate equations for the molecular populations of the masing transition. We use this stability analysis to determine the conditions and parameters for which an astrophysical maser would become unstable. Our results are in agreement with recent observations of astrophysical masers in which fluctuations are found on time scales as short as one thousand seconds.
In Part II statistical methods are applied to analytically calculate the properties of the fluctuations, in intensity and luminosity, of gravitationally lensed images of quasars, due to compact masses lying within the deflecting galaxy. We compute the fluctuations in intensity, and apparent luminosity, of the gravitationally lensed source as measured by quantities such as the standard deviation, autocorrelation function, and power spectrum. We also compare our results with numerical data we received from P. Schneider and A. Weiss, which for the first time directly compares a Monte Carlo type method with a totally analytical calculation.
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