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J. M. Attridge (MIT Haystack Observatory), J. F. C. Wardle (Brandeis University), D. C. Homan (Denison University), R. B. Phillips (MIT Haystack Observatory)
We present new 43 and 86~GHz observations of 3C\,273 and 3C\,279 taken concurrently with the Very Long Baseline Array (VLBA) in May 2002. The VLBA was equipped with seven 86~GHz receivers and ten 43~GHz receivers, effectively yielding similar array resolution at the two frequencies. The new observations confirm the results of the first 86~GHz VLBP observations ever performed (Attridge 2001), and show that though quite challenging, 86~GHz VLBP is a worthwhile scientific pursuit. Improvement of the new images permits further investigation into possible causes of the depolarization seen in quasar cores at high frequencies. As in April 2000, the core of 3C\,273 is completely unpolarized, implying the presence of a strong Faraday screen with rotation measure of greater than 80,000 rad/m2 in or near the core of 3C\,273. The improved resolution of the new May 2002 observations places a limit on the size of any Faraday screen that exists in either the core of 3C\,273 or 3C\,279. In addition, an observed differential Faraday rotation between 43 and 86~GHz across the jet of 3C\,273 implies that a Faraday screen of at least 29,000 rad/m2 must be present approximately 1 milli-arcsecond from the core.
Radio astronomy research at MIT Haystack Observatory is sponsored by the National Science Foundation.
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Bulletin of the American Astronomical Society, 35#5
© 2003. The American Astronomical Soceity.