AAS 201st Meeting, January, 2003
Session 98. AGNs, Black Holes, and Quasars
Oral, Wednesday, January 8, 2003, 10:00-11:30am, 616-617

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[98.05D] A view through Faraday's Fog: Parsec scale Rotation Measures in AGN

R.T. Zavala (New Mexico State University & NRAO), G.B. Taylor (NRAO)

The magnetic field orientations and strengths, and thermal gas densities and pressures can all be probed on parsec scales in active galactic nuclei using VLBA polarimetry. Faraday's Fog, a foreground Faraday rotating medium in the AGN core, is what makes this possible. To take advantage of this effect to explore the central engine we have completed a rotation measure survey of 40 quasars, BL Lac objects, and radio galaxies.

We summarize a few interesting results here. Quasars and radio galaxies show substantial rotation measures (> 1000 rad m-2) but BL Lacertae objects do not. A decreasing core percent polarization appears correlated with an increasing Faraday rotation measure. Faraday depolarization cannot account for this as the rotation measures are approximately two orders of magnitude too small to cause depolarization across an observing bandwidth. A more likely explanation for the depolarization is a gradient in the rotation measure across the synthesized beam. Multi-epoch observations of 3C 279 suggest that rotation measure variations may be tracked over time by changes in the percent polarization. The core rotation measures of the sample appears to be independent of core dominance. We will suggest possible identifications of the Faraday screen.

R.T.Z gratefully acknowledges support from a pre-doctoral research appointment at NRAO and from the New Mexico Alliance for Graduate Education and the Professiorate through NSF grant HRD-0086701.

The author(s) of this abstract have provided an email address for comments about the abstract: rzavala@nrao.edu

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