Natural frequency of the dynamic corona-disk system for a nonrotating black hole with mass M_* = 10 M_⊙ as a function of the mass accretion rate (in units of the Eddington rate) for different values of r_c (panel a) and a (panel b), as indicated in the color bar. Beyond (or below) a certain mass accretion rate, the system reaches a steady state without exhibiting oscillations (dotted black lines). Other parameters used are: a = 0.2 (panel a) and r_c = 30 (panel b), with f = 0.999 in both panels.