  The excitation of an autoionizing resonance by intense radiation requires a
theoretical description beyond the transition probability per unit time. This
implies a time-dependent formulation incorporating all features of the
radiation source, such as pulse temporal shape and duration, as well as
stochastic properties, for pulses other than Fourier limited. The radiation
from short wavelength free electron lasers is a case in point, as it is the
only source that can provide the necessary intensity. In view of ongoing
experiments with such sources, we present a systematic study for an isolated
autoionizing resonance. We find that intensity, pulse duration and field
fluctuations conspire in producing unexpected excitation profiles, not amenable
to a description in terms of the usual Fano profile. In particular, the role of
intensity fluctuations turns out to pose challenging theoretical problems part
of which have been addressed herein.
