Anisotropic inverse Compton scattering in powerful radio galaxies: The case of 3C 295

Inverse Compton (IC) scattering of nuclear photons with relativistic electr ons in the lobes of powerful radio galaxies and quasars can give detectable extended X-ray emission from the radio lobes if relativistic electrons wit h a Lorentz factor gamma < 300 are present (Brunetti et al. 1997). In gener al these electrons are not detected since they emit synchrotron radiation a t frequencies below the radio band, so that the study of this effect provid es a unique tool to measure the energy distribution of the electron populat ion in the radio lobes at <gamma> < 1000 energies. In this paper we reanaly ze the Chandra observation of the powerful and compact radio galaxy 3C 295 for which the IC scattering of nuclear photons is expected to be an importa nt mechanism. We find strong evidence for extended and asymmetrical X-ray e mission associated with the radio lobes in the energy band 0.1-2 keV. We sh ow that both the luminosity and morphology of the extended X-ray emission a ssociated with the radio lobes, not compatible with other X-ray mechanisms, can be best interpreted by the IC scattering with nuclear photons. We also show that the relativistic electron energy distribution obtained from the synchrotron radio emission can be extrapolated down to <gamma> similar to 1 00 thus providing a first direct evidence on the electron spectrum in the l obes down to lower energies.