The Accretion-Ejection Instability has been proposed to explain the
low frequency Quasi-Periodic Oscillation (QPO) observed in
low-mass X-Ray binaries, in particular Black-Hole candidates. Its
frequency, typically a fraction of the Keplerian frequency at the disk
inner radius, is exactly in the range indicated by observations. The
variations of the frequency with the disk inner radius (extracted
from spectral fits of the X-ray emission) might thus be a useful
test. In this paper we discuss how changes in the rotation curve,
due to relativistic effects when the disk approaches the central
object, affect the physics of the instability, and thus this
frequency-inner radius relation. We find that the relationship
between the frequency of the mode and the Keplerian frequency at
the inner disk radius (r_int) departs from the one obtained in a
Keplerian disk, when r_int approaches the last stable orbit. This
might agree with the recently published results, showing a
discrepancy between the behavior of the QPO in the micro quasar
GRO J1655-40, compared to other sources such as XTE
J1550-564 and GRS 1915+105. In a companion paper (Rodriguez
et al. 2002, hereafter Paper I) we have presented detailed
observational results for GRO J1655-40 and GRS 1915+105. We
show how the opposite correlations found in these sources
between the disk color radius (assumed to be close to its inner
radius) and the QPO frequency could indeed be explained by our
theoretical result.
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