  We present a theoretical study of the resonant interaction between dynamical
localized states (discrete breathers) and linear electromagnetic excitations
(EEs) in Josephson junction ladders. By making use of direct numerical
simulations we find that such an interaction manifests itself by resonant steps
and various sharp switchings (voltage jumps) in the current-voltage
characteristics. Moreover, the power of ac oscillations away from the breather
center (the breather tail) displays singularities as the externally applied dc
bias decreases. All these features can be mapped to the spectrum of EEs that
has been derived analytically and numerically. Using an improved analysis of
the breather tail, a spectroscopy of the EEs is developed. The nature of
breather instability driven by localized EEs is established.
