We report on the detection of a statistically significant flare-like event in the Mg II \lambda 2798 Å emission line and the UV Fe II band of CTA 102 during the outburst of autumn 2017 .
The ratio between the maximum and minimum of \lambda 3000 Å continuum flux for the observation period ( 2010 - 2017 ) is 179 \pm 15 .
Respectively , the max/min ratios 8.1 \pm 10.5 and 34.0 \pm 45.5 confirmed the variability of the Mg II emission line and of the Fe II band .
The highest levels of emission lines fluxes recorded coincide with a superluminal jet component traversing through a stationary component located at \sim 0.1 mas from the 43 GHz core .
Additionally , comparing the Mg II line profile in the minimum of activity against the one in the maximum , we found that the latter is broader and blue-shifted .
As a result of these findings , we can conclude that the non-thermal continuum emission produced by material in the jet moving at relativistic speeds is related to the broad emission line fluctuations .
In consequence , these fluctuations are also linked to the presence of broad-line region ( BLR ) clouds located at \sim 25 pc from the central engine , outside from the inner parsec , where the canonical BLR is located .
Our results suggest that during strong activity in CTA 102 , the source of non-thermal emission and broad-line clouds outside the inner parsec introduces uncertainties in the estimates of black hole ( BH ) mass .
Therefore , it is important to estimate the BH mass , using single-epoch or reverberation mapping techniques , only with spectra where the continuum luminosity is dominated by the accretion disk .