Abstract
We consider the evolution of a spherically expanding plasma cloud, where there is a continuous injection of nonthermal electrons. We compute the time-dependent electron distribution and resultant photon spectra taking into account synchrotron, adiabatic, and inverse Compton cooling. This model is different from previous works where, instead of a continuous injection of particles, a short injection period was assumed. We apply this model to the radio/optical knots in the large-scale jets of active galactic nuclei, detected in X-rays by Chandra, and find that the overall broadband spectral features can be reproduced. It is shown that for some sources, constraints on the X-ray spectral index (by a longer Chandra observation) will be able to differentiate between the different models. This in turn will put a strong constraint on the acceleration mechanism active in these sources.
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