Based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc. under NASA contract No. NAS5-26555. These observations are associated with proposals #5980 and #7848. Also based on observations obtained at the NRAO's VLA. The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc.

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Present address: Fermilab MS 127, PO Box 500, Batavia IL 60510, USA.

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... outward

For the conversion of angular to physical scales, we assume a flat cosmology with $\Omega_{{\rm m}}=0.3$ and H₀ = h₇₀ $\times$ $70~{\rm km~s^{-1}~Mpc^{-1}}$ , leading to a scale of $2.7~h_{70}^{-1}~{\rm kpc}$ per second of arc at 3C 273's redshift of 0.158.

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... index

We define the spectral index $\alpha$ such that $f_\nu \propto \nu^{\alpha}$ .

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... mechanism

Slightly larger breaks may be possible by assuming certain source conditions, systematically varying magnetic fields, for example (Wilson 1975).

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