Astronomy and Astrophysics – Astronomy
Scientific paper
Sep 1999
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999astl...25..555m&link_type=abstract
Astronomy Letters, Volume 25, Issue 9, September 1999, pp.555-568
Astronomy and Astrophysics
Astronomy
4
Scientific paper
The fine structure of the AGN objects 3C345 and 1803+784 is studied. Their jets are shown to have conical helical structures. The helix diameter and pitch are proportional to the distance from the nucleus (injector). The helix axis is curved. This structure is attributable to a short- and long-period precession of the accretion-disk rotation axis. The jet is cocooned in a thin layer of thermal plasma with l approximately equal to 0.01 pc, whose transparency increases as one recedes from the nucleus. The thermal-electron density in the cocoon wall near the nuclear region N_e is equal to or exceeds 10^6 cm^{-3}. The nuclear activity causes the cocoon transparency to change, which results in a low-frequency variability of radio emission from the quasars and in a change of polarization parameters. The cocoon transparency determines the visible part of the jet and "displaces" the nucleus from the injector. The nucleus is a compact, bright region of the jet, whose brightness temperature does not exceed the Compton limit. The jet spectrum exhibits a low-frequency cutoff. The cutoff frequency in the spectrum of the nuclear region lies at short centimeter wavelengths and shifts to lower frequencies as one recedes from the injector. The low-frequency spectral index is steep and reaches alpha = 4, which is attributable to additional absorption of synchrotron radiation in the cocoon wall. The high-frequency spectral index is typical of optically thin sources and is alpha = -1.5 at large distances from the nucleus.
Matveyenko L. I.
Witzel A. I.
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