  We demonstrate for the first time that the effect of fullerene shell upon
photoionization of the "caged" atom in an endohedral can result in formation of
Giant Endohedral Resonances or GER. This is illustrated by the concrete case of
Xe@C60 photoionization cross-section that exhibits at 17 eV a powerful
resonance with total oscillator strengths of about 25. The prominent
modification of the 5p6 electron photoionization cross-section of Xe@C60 takes
place due to strong fullerene shell polarization under the action of the
incoming electromagnetic wave and oscillation of this cross-section due to the
reflection of the photoelectron from Xe by the C60. These two factors transform
the smoothly decreasing 5p6 cross-section of Xe into a rather complex curve
with a powerful maximum for Xe@C60, with the oscillator strength being equal to
25! We present also the results for the dipole angular anisotropy parameter
that is strongly affected by the reflection of the photoelectron waves but not
modified by C60 polarization. The polarization of C60 is expressed via its
total photoabsorption cross-section. The reflection of the photoelectron is
taken into account in the frame of the so-called bubble potential that is a
spherical delta-type potential.
