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The nearby radio galaxy Centaurus A is poorly studied at high frequencies with conventional radio telescopes because of its very large angular size, but is one of a very few extragalactic objects to be detected and resolved by the  Wilkinson Microwave Anisotropy Probe  ( WMAP ). We have used the five‐year  WMAP  data for Cen A to constrain the high‐frequency radio spectra of the 10° giant lobes and to search for spectral changes as a function of position along the lobes. We show that the high‐frequency radio spectra of the northern and southern giant lobes are significantly different: the spectrum of the southern lobe steepens monotonically (and is steeper further from the active nucleus) whereas the spectrum of the northern lobe remains consistent with a power law. The inferred differences in the northern and southern giant lobes may be the result of real differences in their high‐energy particle acceleration histories, perhaps due to the influence of the northern middle lobe, an intermediate‐scale feature which has no detectable southern counterpart. In light of these results, we discuss the prospects for  Fermi Gamma‐ray Space Telescope  detections of inverse‐Compton emission from the giant lobes and the lobes' possible role in the production of the ultra‐high‐energy cosmic rays (UHECR) detected by the Pierre Auger Observatory. We show that the possibility of a  Fermi  detection depends sensitively on the physical conditions in the giant lobes, with the northern lobe more likely to be detected, and that any emission observed by  Fermi  is likely to be dominated by photons at the soft end of the  Fermi  energy band. On the other hand, we argue that the estimated conditions in the giant lobes imply that UHECRs can be accelerated there, with a potentially detectable γ‐ray signature at TeV energies.

High‐energy particle acceleration and production of ultra‐high‐energy cosmic rays in the giant lobes of Centaurus A