The Dynamic Age of Centaurus A

In this paper I present dynamic models of the radio source Centaurus A, and critique possible models of in situ particle reacceleration (ISR) within the radio lobes. The radio and gamma-ray data require neither homogeneous plasma nor quasi-equipartition between plasma and magnetic field; inhomogeneous models containing both high-field and low-field regions are equally likely. Cen A cannot be as young as the radiative lifetimes of its relativistic electrons, which range from a few to several tens of Myr. Two classes of dynamic models -- flow driven and magnetically driven -- are consistent with current observations; each requires Cen A to be on the order of a Gyr old. Thus, ongoing ISR must be occurring within the radio source. Alfven-wave ISR is probably occurring throughout the source, and may be responsible for maintaining the gamma-ray-loud electrons. It is likely to be supplemented by shock or reconnection ISR which maintains the radio-loud electrons in high-field regions.