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Thesis (Ph. D.)--University of Texas at Austin, 2002. / Vita. Includes bibliographical references. Available also from UMI Company.

Thesis--University of Florida. / Description based on print version record. Typescript. Vita. Bibliography: leaves 349-355.

Thesis (Ph. D)--University of Florida, 1981. / Description based on print version record. Typescript. Vita. Includes bibliographical references (leaves 155-157).

This thesis is concerned with the physics of extragalactic radio - sources. Radio observations of a given source provide a powerful method with which to make direct measurements of the physical processes occuring within the la~ge-scale radio lobes and hotspots . Multi-frequency observations with up to five frequencies have been made for a number of ~ources using the Cambridge 5-km telescope and the Very Large Array. These data have been used to determine the change in radio spectra across the source . to obtain information about the way in which the electron population has evolved. Combining this with inferred magnetic field directions, the dynamics of seven sources have been examined. Additionally the hotspot advance speeds for a statistically representative sample of sources have -been derived. For 3C234 it was possible to test the assumptions used throughout the analysis. They were found to h6ld good to within the limits of error. The results are best interpreted within the framework of a fluid-dynamical model lobes as have recently been examined in numerical experiments. The general distibution of radiating plasma can be understood in terms of the flow of material out of the main accelerating regions (the hotspots - a basic beam model � is assumed thr6ughout) and its subsequent interaction with the surrounding medium, coupled with some precession of the radio jet. As well as looking at source dynamics , the detailed spectra have been used to search for areas of particle acceleration not associated with hotspots. Three sources have been found to have such regions, but large scale acceleration within the radio-lobes is not required . The derivation of ho tspot advance speed for a statistically representative sample has enabled statistical correlations to be investigated . Advance speed is found to be strongly correlated with power and this is discussed in the wider context of overall source models.

Observations have been carried out to survey the northern galactic plane for sources of highly variable radio emission at 5 GHz. To over—come the biases of previous searches for variability, the survey is conducted by making repeated and systematic observations of the survey region, consisting of the area within about ±2° of the galactic plane in the longitude interval of 40° to 220°. This thesis presents the analysis and results of the first three years of observations, comprising 40% of the total survey. The observations were carried out for a total of 3 months, in August of 1977, 1978 and 1979, and cover an area of over 200 square degrees, with a resolution of 3'. Within this area, a total of 806 compact radio sources have been detected. The catalogue includes sources with flux density as low as 15 mJy, and is complete down to 70 mJy. Of these sources, 758 have been examined for variation on a time scale of a few days (short—term), and 434 for variations on time scales of one or two years (long—term). Twenty—three new variable radio sources have been discovered; 12 short—term and 11 long—term. An additional 18 sources are possibly variable. The amplitudes of the long—term variations are similar to those of known extragalactic variables. A number of short—term variables exhibit much larger variations. The longitude distribution suggest that the majority of short—term variables are galactic, with luminosities in the range 10³⁰—10³⁵ ergs—s⁻¹. This luminosity range is similar to that of the strong X—ray binaries sources, such as Cyg X-3, SS 433 and Sco X-1. To date, extensive follow—up observations have been carried out for only one of the variable sources discovered. This source (GT0236+610) is periodic, undergoing a radio outburst every 26.52 days. The source is positionally co-incident with the BO star LS 1+61°303 and this identification has been confirmed by Gregory et al. (1979). GT0236+610 is an X-ray source (Share et al. 1978, Bignami et al. 1980) and, in addition, is the most probable counterpart of the COS B ƴ-ray source CG135+01 (Gregory and Taylor 1978, Pollock et al. 1981 ). Another highly variable source (GT2116+493) is also found to be co—incident with a stellar object. This source is probably an RS CVn type binary at a distance of about 300 pc. Comparison of source counts from the catalogue of compact sources, to extragalactic results, show that >200 of the compact sources, with flux density less than 60 mJy, are galactic. The non—variable galactic sources are likely to be small HII regions within 6 kpc of the sun. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

A description and the results of two surveys to search for highly variable radio emission in the galactic plane are presented. The surveys were carried out by making daily beamswitched maps of the survey regions and comparing the results of each day to the average of all days for evidence of variability. The first survey, at 21 cm, maps an area of 86 sq. deg. of the local spiral arm, in the direction of the constellation Cygnus, and searches for variability to a sensitivity of ~ 0.3 Jy. The second survey, at 6 cm, covers an area of 56 sq. deg. in the galactic longitude range (ℓˡˡ) 40°- 140°. The study of variability in this survey is not yet complete but variations at a level of ~10 mJy are expected to be measurable. It is concluded that large intensity variations (greater than ~ 1 Jy) on a time scale of days are extremely rare; only one possible variation at a level of 0.9 Jy was detected during the 52 days of the 21 cm survey. A preliminary examination of the 6 cm data reveals one highly variable radio source, designated GT 0236+610, that reached a maximum flux density of 285 mJy. The results of further observations of this source are presented. The 6 cm observations were averaged over the complete survey period and the data were searched for compact sources down to a level of 10 - 20 mJy. The positions and 6 cm flux density for the resulting 196 compact sources are listed. / Science, Faculty of / Physics and Astronomy, Department of / Graduate