  In this paper we introduce a method to resolve transient excitations in
time-frequency space from molecular dynamics simulations. Our technique is
based on continuous wavelet transform of velocity time series coupled to a
threshold-dependent filtering procedure to isolate excitation events from
background noise in a given spectral region. By following in time the center of
mass of the reference frequency interval, the data can be easily exploited to
investigate the statistics of the burst excitation dynamics, by computing, for
instance, the distribution of the burst lifetimes, excitation times, amplitudes
and energies. As an illustration of our method, we investigate transient
excitations in the gap of NaI crystals at thermal equilibrium at different
temperatures. Our results reveal complex ensembles of transient nonlinear
bursts in the gap, whose lifetime and excitation rate increase with
temperature. The method described in this paper is a powerful tool to
investigate transient excitations in many-body systems at thermal equilibrium.
Our procedure gives access to both the equilibrium and the kinetics of
transient excitation processes, allowing one in principle to reconstruct the
full picture of the dynamical process under examination.
