Panel a: observed period of the SMBHB system in years as a function of the primary mass fraction and of the decadic logarithm of the orbital separation of the black holes in milliparsecs. The considered total black hole mass is M_tot = 3 × 10⁸ M_⊙ according to Padovani et al. (2019). The plot represents the complete parameter space in terms of that would yield the observed disk-jet precession period of 10 yr. Panel b: color-coded merger timescale in years as a function of the primary black hole mass ratio x_p and of the decadic logarithm of the mutual component distance r_ps in milliparsecs. The whole parameter space (x_p, r_ps) is shown that yields merger timescales longer than the source-frame SMBHB orbital period, τ_merge >  P_ps.