  We have analyzed AstroSat observations of the galactic micro-quasar system
GRS 1915+105, when the system exhibited C-type Quasi-periodic Oscillations
(QPOs) in the frequency range of 3.4-5.4 Hz. The broad band spectra (1-50 keV)
obtained from simultaneous LAXPC and SXT can be well described by a dominant
relativistic truncated accretion disk along with thermal Comptonization and
reflection. We find that while the QPO frequency depends on the inner radii
with a large scatter, a much tighter correlation is obtained when both the
inner radii and accretion rate of the disk are taken into account. In fact, the
frequency varies just as the dynamic frequency (i.e. the inverse of the sound
crossing time) as predicted decades ago by the relativistic standard accretion
disk theory for a black hole with spin parameter of ~0.9. We show that this
identification has been possible due to the simultaneous broad band spectral
coverage with temporal information as obtained from AstroSat.
