AAS Meeting #194 - Chicago, Illinois, May/June 1999
Session 73. AGN: Radio Galaxies, QSO's and Blazars
Display, Wednesday, June 2, 1999, 10:00am-6:30pm, Southeast Exhibit Hall

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[73.01] MERLIN observations of optical jets and hotspots

A. R. Martel (STScI), J. P. Leahy (U. Manchester/STScI), S. A. Baum, J. A. Biretta, W. B. Sparks (STScI)

The HST WFPC2 3CR snapshot survey discovered a number of new cases of optical synchrotron emission from radio jets and hotspots, and provided high-resolution images of some previously known cases. Because the HST images have significantly higher resolution than existing (VLA) radio images, we are observing all these objects with MERLIN, which has seven times longer baselines than the VLA A-configuration. This gives a resolution of 50 milli-arcsec at 5 GHz and 0.14 arcsec at 1.7 GHz, close to the effective resolutions of the PC and WFC chips respectively. In most cases we have observed at both 5 and 1.7 GHz. In addition to the original F702W (R) survey images, most targets have been re-observed with the F555W (V) filter; hence we can separately determine radio, radio-optical, and optical spectral indices. In this paper we present results on the jets of 3C 15, 3C 78, and 3C 200, and the hotspots in 3C 213.1 and 3C 20. We compare the general steepening of the spectrum along the jets to synchrotron ageing models. The structure of the jets and lobes in these objects is diverse, ranging from the classic diffuse FR I jet of 3C 78 to the highly collimated one in 3C 200, whose radio power is comparable to nearby quasars. In all three jets the spectrum steepens systematically with distance from the center, consistent with most of the particle acceleration occurring at the nucleus, provided flow speeds are relativistic. The hotspots also are clearly more compact in the optical than in the radio, supporting the notion that particle acceleration is confined to a small region near the end of the jets. This work was supported by GO-05.95700; MERLIN is operated by the University of Manchester as a national facility of PPARC.

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