  Galactic black hole candidates GRS 1915+105 and IGR J17091-3624 have many
similarities in their light curves and spectral properties. However, very
little is known about the orbital elements of their companions. In case the
orbits are eccentric, tidal forces by the black hole on the companion can cause
modulations of accretion rates in orbital time scale. We look for these
modulations in the light curves of these two objects and find that their
periodicities are around 28.3 d (29.0 d) and 32.2 d respectively.
Eccentricities are at the most 0.071 and 0.46 respectively. We conclude that
both these objects have long orbital periods and are eccentric. This could be a
reason why light curves have several similar variability class transitions as
reported in the literature.
