Astronomy and Astrophysics – Astronomy
Scientific paper
Dec 2004
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004aas...20517804g&link_type=abstract
American Astronomical Society Meeting 205, #178.04; Bulletin of the American Astronomical Society, Vol. 37, p.381
Astronomy and Astrophysics
Astronomy
Scientific paper
Periodic variability of the Doppler effect is examined in helical jet models of radio-loud active galaxies. Helical motion in jets cause periodic changes in the direction of relativistic flow with respect to the line of sight. Relativistic Doppler factors are computed for different values of bulk Lorentz factor, direction of jet axis, jet radius, and helicity. It is shown that angles with respect to the line of sight can change up to 20 degrees due to helical motions similar to those observed in radio-loud quasars. Such changes in the direction of flow can result in Doppler factors varying by a factor of 10. Components undergoing this motion can have peak frequencies that vary by a factor of 10 and fluxes that vary by a factor greater than 100. It is apparent that components in helical jets can alter the radio spectra of quasars and BL Lac objects as a result of their motion on timescales from years to decades. Next, the properties of a sample of inverted-spectrum radio sources are compared to helical jet models. The radio spectra and variability of these sources can be explained in part by helical jets. Also, the impact of these models on observed polarization and predictions to the foreground of Cosmic Microwave Background anisotropy experiments will be discussed.
This work supported in part by the Lindback Foundation and Rowan University.
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