Fig. 3. Confidence contours for the mass, radius, and mass accretion rate indices.

We show the confidence contours for the dependency of the characteristic bend frequency on the accretor mass, radius, and mass accretion rate indices. We have fitted the model, log ν_b = A log R + B log M + C log $\dot{\mathit{M}}$ + D, where ν_b represents the measured characteristic bend frequencies, and R, M, and $\dot{\mathit{M}}$ are the radii, masses, and mass accretion rates, respectively (all using cgs units), to determine the best-fit values for A, B, C, and D. The obtained fit is good (X² = 38.41 for 37 df) and consistent with the previously obtained fit (1), resulting in A = −2.07 ± 0.11, B = 0.043 ± 0.17, C = 0.95 ± 0.22, and D = −3.07 ± 2.61. The dark gray lines show the previously obtained fit using a BH-only sample (1), with 1σ errors marked with light gray regions. Given that the previous fit was solely based on BHs, a degeneracy between mass and radius existed, such that it was essentially fitting for ν_b ∝ R^aM^b and the finding that a + b ≈ −2. The contours refer to the fit including accreting WDs, AGN, and soft-state Galactic BHs and allowing the radius to be an additional free parameter. We thus show that the dominant parameter in the scaling law is a characteristic radius in the inner disc, and not the mass of the accretor as previously thought.