Polarization observations of the radio cores of AGN - I. A sample of quasars

Details Polarization observations of the radio cores of AGN - I. A sample of quasars Polarization observations of the radio cores of AGN - I. A sample of quasars

Aug 1998

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998mnras.298..877s&link_type=abstract

Monthly Notices of the Royal Astronomical Society, Volume 298, Issue 3, pp. 877-887.

Astronomy and Astrophysics

Astronomy

15

Polarization, Galaxies: Active, Galaxies: Nuclei, Quasars: General, Radio Continuum: Galaxies

Scientific paper

We present total-intensity and linear-polarization observations at a single epoch for a sample of 11 quasars and one BL Lac object. The data were taken with the VLA A array at λλ20, 18, 6 and 2 cm. We examine the variation of the degree of polarization, p, and polarization position angle, PA, with wavelength, and attempt to determine the rotation measure, RM, of the cores in these sources. The degree of polarization does not exhibit any systematic variation with wavelength, the median values ranging from 2.3 to 3.5 per cent at the different wavelengths. The variation of PA with λ2 is not linear over the entire wavelength range. However, for most sources the λλ20-, 18- and 6-cm PAs do follow such a linear relationship, yielding a median |RM| of about 15 rad m-2. In contrast, the λλ6- and 2-cm observations give a median |RM| of about 129 rad m-2. The long-wavelength emission is likely to originate from a spatially different part of the milliarcsec-scale jet from the λ2-cm emission, which could turn over at a higher frequency and is likely to be more compact and located closer to the quasar nucleus. We have attempted to obtain linear fits over the entire wavelength range allowing for nπ ambiguities in the PAs, but the fits are not statistically significant. The low values of RM for these core-dominated sources suggest that either the radio emission from the jet intercepts few of the emission-line clouds and their confining medium, or the clouds have a small filling factor and are possibly magnetically confined.

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