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Session 13 - Observations of Radio Sources.
Display session, Monday, January 15
North Banquet Hall, Convention Center

[13.03] Disentangling Relativistic Effects in Compact Radio Sourcs

E. J. Guerra, R. A. Daly (Princeton U.)

Compact radio sources can be strongly affected by relativistic motion. Relativistic motion is indicated by apparent superluminal motion, one-sidedness of jets, rapid flux variations, and a deficit of synchrotron self-Compton X-rays. The relativistic motion is characterized by 2 quantities: the speed of the outflow relative to the speed of light \beta, and the angle subtended by the velocity vector and the line of sight to the observer \theta.

One combination of these parameters is given by superluminal motion studies, which indicate an apparent velocity \beta_app = \beta \sin\theta/(1-\beta \cos\theta). Another combination of these parameters is given by the Doppler factor of the outflow \delta = \sqrt1-\beta^2/(1-\beta \cos\theta). Thus, \beta and \theta can be estimated separately for sources with an estimate of both \beta_app and \delta.

The Doppler factor of the outflow \delta can be estimated in 2 ways. The inverse Compton Doppler factor \delta_IC is obtained by comparing the radio and X-ray flux density of a source, and is so named because the X-rays are produced by the synchrotron self-Compton process. The equipartition Doppler factor \delta_eq can be estimated using single-epoch radio observations, and is obtained by setting the magnetic field strength equal to the equipartition value in the expression that relates the observed peak flux density, the peak frequency, the angular size of the source, the Doppler factor, and the source magnetic field (see Readhead 1994).

We have a sample of 43 sources with an estimate of \beta_app from superluminal motion studies, and estimates of \delta_eq and \delta_IC; the sample includes 8 BL Lac objects, 8 core-dominated high-polarization quasars, 10 core-dominated low-polarization quasars, 3 core-dominated quasars without polarization information, 7 lobe-dominated quasars, and 7 radio galaxies. The data have been used to study \beta and \theta for different categories of sources. Several interesting trends emerge. The redshift behavior of various quantities is also investigated. These results have implications for orientation unified models and for selection effects inherent in the radio catalogues. These results will be presented and discussed.

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