The quasar 3C454.3 underwent a uniquely-structured multi-frequency outburst in June 2016. The blazar was observed in the optical $R$ band by several ground-based telescopes in photometric and polarimetric modes, at $gamma$-ray frequencies by the emph{Fermi} Large Area Telescope, and at 43 GHz with the Very Long Baseline Array. The maximum flux density was observed on 2016 June 24 at both optical and $gamma$-ray frequencies, reaching $S^mathrm{max}_mathrm{opt}=18.91pm0.08$ mJy and $S_gamma^mathrm{max} =22.20pm0.18times10^{-6}$ ph cm$^{-2}$ s$^{-1}$, respectively. The June 2016 outburst possessed a precipitous decay at both $gamma$-ray and optical frequencies, with the source decreasing in flux density by a factor of 4 over a 24-hour period in $R$ band. Intraday variability was observed throughout the outburst, with flux density changes between 1 and 5 mJy over the course of a night. The precipitous decay featured statistically significant quasi-periodic micro-variability oscillations with an amplitude of $sim 2$-$3%$ about the mean trend and a characteristic period of 36 minutes. The optical degree of polarization jumped from $sim3%$ to nearly 20% during the outburst, while the position angle varied by $sim120degr$. A knot was ejected from the 43 GHz core on 2016 Feb 25, moving at an apparent speed $v_mathrm{app}=20.3cpm0.8c$. From the observed minimum timescale of variability $tau_mathrm{opt}^mathrm{min}approx2$ hr and derived Doppler factor $delta=22.6$, we find a size of the emission region $rlesssim2.6times10^{15}$ cm. If the quasi-periodic micro-variability oscillations are caused by periodic variations of the Doppler factor of emission from a turbulent vortex, we derive a rotational speed of the vortex $sim0.2c$.
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