Radio Polarization and Spectra of Variable Extragalactic Objects

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Frequent measurements of the total flux density and linear polarization of extragalactic radio sources will be made at a frequency of 4.8, 8.0 and 14.5 GHz using the Michigan 26 meter radio telescope. Theoretical models will be developed and fitted to these data to study the physical conditions in the emitting regions and to study the particle energy generation mechanisms. These observations will be supplemented by Very Long Baseline Interferometry (VLBI) observations in collaboration with other researchers. Observations will also be made at 0.85, 1.4 and 2.7 GHz with the National Radio Astronomy Observatory 91 meter telescope to investigate the broad-band characteristics of low- frequency variable sources. Specific objectives of the research include: a) to obtain high time-resolution, multifrequency polarization and flux density data of isolated outbursts in order to test detailed theoretical models of the source emitting region, b) to develop more sophisticated models of shocks propagating in relativistic jet flows which constrain more of the physical parameters of the emitting regions, c) to better understand the relative importance of intrinsic and extrinsic and mechanisms as causes of decimetric variability, and the nature of the "intermediate frequency gap" , d) to improve global models of active galactic nuclei through simultaneous, broad- band (Ultraviolet or X-ray through radio wavelengths) observations, and e) to obtain morphological information of selected sources to test models of the emitting regions.