  The spectral and timing properties of an oscillating hot thermal corona are
investigated. This oscillation is assumed to be due to a magneto-acoustic wave
propagating within the corona and triggered by an external, non specified,
excitation. A cylindrical geometry is adopted and, neglecting the rotation, the
wave equation is solved in for different boundary conditions. The resulting
X-ray luminosity, through thermal comptonization of embedded soft photons, is
then computed, first analytically, assuming linear dependence between the local
pressure disturbance and the radiative modulation. These calculations are also
compared to Monte-Carlo simulations. The main results of this study are: (1)
the corona plays the role of a low band-pass medium, its response to a white
noise excitation being a at top noise Power Spectral Density (PSD) at low
frequencies and a red noise at high frequency, (2) resonant peaks are present
in the PSD. Their powers depend on the boundary conditions chosen and, more
specifically, on the impedance adaptation with the external medium at the
corona inner boundary. (3) The flat top noise level and break as well as the
resonant peak frequencies are inversely proportional to the external radius rj.
(4) Computed rms and f-spectra exhibit an overall increase of the variability
with energy. Comparison with observed variability features, especially in the
hard intermediate states of X-ray binaries are discussed.
