  We report exact results for the Fermi Edge Singularity in the absorption
spectrum of an out-of-equilibrium tunnel junction. We consider two metals with
chemical potential difference V separated by a tunneling barrier containing a
defect, which exists in one of two states. When it is in its excited state,
tunneling through the otherwise impermeable barrier is possible. We find that
the lineshape not only depends on the total scattering phase shift as in the
equilibrium case but also on the difference in the phase of the reflection
amplitudes on the two sides of the barrier. The out-of-equilibrium spectrum
extends below the original threshold as energy can be provided by the power
source driving current across the barrier. Our results have a surprisingly
simple interpretation in terms of known results for the equilibrium case but
with (in general complex-valued) combinations of elements of the scattering
matrix replacing the equilibrium phase shifts.
