Other
Scientific paper
Dec 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995aas...187.1303g&link_type=abstract
American Astronomical Society, 187th AAS Meeting, #13.03; Bulletin of the American Astronomical Society, Vol. 27, p.1301
Other
Scientific paper
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 θ/(1-beta cos θ). Another combination of these parameters is given by the Doppler factor of the outflow delta = sqrt {1-beta (2}/(1-beta ) cos θ). 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.
Daly Ruth A.
Guerra Erick J.
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