We studied a reproducible fine structure observed in dynamic conductance spectra of Andreev arrays in Sm$_{1-x}$Th$_x$OFeAs superconductors with various thorium concentrations ($x = 0.08 - 0.3$) and critical temperatures $T_c = 26-50$,K. This structure is unambiguously caused by a multiple boson emission (of the same energy) during the process of multiple Andreev reflections. The directly determined energy of the bosonic mode reaches $varepsilon_0 = 14.8 pm 2.2$,meV for optimal compound. Within the studied range of $T_c$, this energy as well as the large $Delta_L$ and the small $Delta_S$ superconducting gaps, nearly scales with critical temperature with the characteristic ratio $varepsilon_0/k_BT_c approx 3.2$ (and $2Delta_L/k_BT_c approx 5.3$, correspondingly) resembling the expected energy $Delta_L + Delta_S$ of spin resonance and spectral density enhancement in $s^{pm}$ and $s^{++}$ states, respectively.
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