Synchrotron Aging in Filamented Magnetic Fields

Abstract

Magnetic -elds in synchrotron sources are almost certainly inhomogeneous, mixing high--eld and low--eld 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 -nd these critical frequencies are higher than would be the case if the electrons were con- -ned to a homogeneous high--eld region. We apply our results to the interpretation of extragalactic radio sources whose dynamical ages are known to be signi-cantly greater than the ages inferred from their high-frequency spectral breaks. Subject headings: ISM: magnetic -elds È radiation mechanisms: nonthermal