| It is widely believed that the low-frequency quasi-periodic X-ray oscillations observed in microquasars are correlated to, but do not originate at, the physical radius of the inner edge of the accretion disk. Models relating the quasi-periodic oscillation (QPO) frequency and color radius are hindered by observations showing contradicting trend correlations between the microquasars GRO 1655–40, XTE J1550–564, and GRS 1915+105. The first shows a negative correlation and the latter two a positive one. By taking into account relativistic rotation in the accretion disk, the accretion-ejection instability (AEI) model predicts a turnover in the frequency-radius relationship, and has been successfully compared with observations of GRO J1655–40 and GRS 1915+105. We present further evidence supporting the AEI model prediction by using observations of the microquasar GRS 1915+105. By combining a data set including θ-, β-, and α-class X-ray light curves, we observe positive, negative, and null correlations in the frequency-radius relationship. This is the first time a single source has shown a possible inversion in the QPO frequency-color radius curve predicted by the AEI model. |
