Astronomy and Astrophysics – Astronomy
Scientific paper
May 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011aas...21832715r&link_type=abstract
American Astronomical Society, AAS Meeting #218, #327.15; Bulletin of the American Astronomical Society, Vol. 43, 2011
Astronomy and Astrophysics
Astronomy
Scientific paper
Deep Very Large Array imaging of the quasar 3C345 has been used to study the structure, linear polarization, and magnetic field of its radio jet at 4.86 and 8.44 GHz on scales ranging from 2 to 30 kpc. There is a 7-8 Jy unresolved core with spectral index -0.24. The jet (typical intensity 15 mJy/beam) consists of a 2.5 arcsec straight section containing two knots, and two additional non-co-linear knots at the end. The spectral index of the jet varies between -1.1 and -0.5. The main body of the jet diverges slightly, with an apparent opening half-angle of about 8 degrees; de-projected, the intrinsic opening angle is probably about 1-2 degrees. Surprisingly, the inferred magnetic field direction in the interior of the main body of the jet is neither longitudinal nor transverse, but makes an angle of about 55 degrees with the jet axis, in an apparent helix. There is no significant Faraday rotation in the source, so that is not the cause of the field twist. The fractional polarization in the jet averages 25%, while that of the core is only 3%. Despite the indication of jet precession in the total intensity structure, the polarization images suggest instead a jet re-directed at least twice by collisions with the external medium. Simple models of magnetized jets are investigated in order to study various possible origins of the magnetic field morphology. In a cylindrically symmetric transparent jet a helical magnetic field would appear either transverse or longitudinal due to partial cancellations of Stokes parameters. Synchrotron opacity can break the symmetry, but it leads to fractional polarization far less than that observed. We investigate whether differential Doppler boosting in a diverging jet can break the symmetry, allowing a truly helical jet to appear helical.
Marchenko Valerie V.
Roberts David H.
Wardle John F. C.
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