1997. The American Astronomical Society. All rights reserved. Printed in U.S.A.( SYNCHROTRON AGING IN FILAMENTED MAGNETIC FIELDS

Magnetic Ðelds in synchrotron sources are almost certainly inhomogeneous, mixing high-Ðeld and low-Ðeld regions. This inhomogeneity a†ects the evolution of a relativistic electron distribution function due to the rate of energy loss of the electrons changing as they move between the two regions. We present two models for the evolution of the distribution function, and discuss the results of these models in terms of the critical energies, or synchrotron frequencies, where the particle and photon spectra steepen. We Ðnd these critical frequencies are higher than would be the case if the electrons were con-Ðned to a homogeneous high-Ðeld region. We apply our results to the interpretation of extragalactic radio sources whose dynamical ages are known to be signiÐcantly greater than the ages inferred from their high-frequency spectral breaks. Subject headings: ISM: magnetic Ðelds È radiation mechanisms: nontherma