Date of Award

4-17-2007

Document Type

Thesis open access

Abstract

We are conducting a Very Long Baseline Interferometer (VLBI) survey of a complete sample of 25 lobe-dominated quasars, with the goal of testing relativistic jet models. Since the quasars 3C207 and 3C245 have the most prominent parsec-scale jets, we have observed them intensively with the Very Long Baseline Array (VLBA) from 2003 to 2005 at 15 and 22 GHz. Data from observations made of 3C245 at 22 GHz were not usable due to the weak flux density of the source. We find superluminal motion in 3C207 when observing at 15 GHz, increasing from 2 to 3 times the speed of light (2-3c) in the inner jet (less than 1 milliarcsecond [mas] from the core) to ~11c in the outer (2 mas) jet. The jet is curved, decreasing in position angle (PA) by 10o approximately 2 mas away from the core. A Lorentz factor (γ) of 10, and an increase in angle to the line of sight from &#;&#;&#;&#;1o to 6o outward along the jet, are consistent with the observed speeds and fluxes. Observations of 3C207 at 22 GHz yielded results inconsistent with the observations made at 15 GHz and with large uncertainties, due to the limited number of observations. We therefore could not draw any definitive conclusions about the motion of the 3C207 from observations made at 22 GHz. We also find superluminal motion in 3C245, with speeds alternating in the pattern 3c, 8c, 5c, 11c, and 4c outward along the inner three mas of the jet. There is a mild oscillation in PA with amplitude ~5o. These observations are more difficult to interpret. A choice of &#;&#;= 10, and oscillations between &#;&#;= 1o and 6o, are consistent with the observed speeds and fluxes, but the probability that two of our sources would have such small &#; is very low. The speeds could also arise from oscillations between &#;&#;= 6o and 35o, but the predicted large range of Doppler-boosted component fluxes is not observed. A range of Lorentz factors, or acceleration along the jet, permits alternative interpretations. We are grateful for support from an AAS Small Research Grant.

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