3C 454.3 FeII, MgII & 3000{AA} measurements

In this work, we perform multiwavelength analysis from radio to gamma-rays and study the MgII {lambda}2798 emission line and the UV FeII band from 2008 to 2018. We found that an increase in the 43GHz flux density of the quasi-stationary component C coincides with the estimated time at which a superluminal blob ejected from the radio core (which caused the brightest flare of 2010) collides with the quasi-stationary component (at a projected distance of ~4.6pc from the radio core).

The different behavior of the spectral index in the first (5000<JD-2,450000<5600) and second (6600<JD-2450000<7900) flaring periods suggests changes in the physical conditions. The complex nature of the second period can be a result of a superposition of multiple events at different locations. The MGII line has an anticorrelation with the UV continuum while Fe ii correlates positively, except at the time of the brightest flare of 2010, when both have a strong response at high continuum luminosities.