Giant Lobes of Centaurus A as Seen in Radio and Gamma-Ray Images Obtained with the Fermi-LAT and Planck Satellites

The gamma-ray data of Fermi-LAT on the giant lobes of Centaurus A are analysed together with the high frequency radio data obtained with the Planck satellite. The large gamma-ray photon statistics, accumulated during seven years of observations, and the recently updated Fermi-LAT collaboration software tools allow substantial extension of the detected gamma-ray emission towards higher energy, up to 30 GeV, and lower energy, down to 60 MeV. Moreover, the new gamma-ray data allow us to explore the spatial features of gamma-ray emission of the lobes. For the north lobe, we confirm, with higher statistical significance, our earlier finding on the extension of gamma-ray emission beyond the radio image. Moreover, the new analysis reveals significant spatial variation of gamma-ray spectra from both lobes. On the other hand, the Planck observations at microwave frequencies contain important information on spectra of synchrotron emission in the cutoff region, and thus allow model-independent derivation of the strength of the magnetic field and the distribution of relativistic electrons based on the combined gamma-ray and radio data. The interpretation of multiwavelength spectral energy distributions (SEDs) of the lobes within a pure leptonic model requires strong enhancement of the magnetic field at the edge of the south lobe. Alternatively, a more complex, leptonic-hadronic model of the gamma-ray emission, postulating a non-negligible contribution of the pi(0)-decay component at highest energies, can explain the gamma-ray data with a rather homogeneous distribution of the magnetic field over the giant lobes