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 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 } } = 18.91 \pm 0.08 mJy and S _ { \gamma } ^ { \mathrm { max } } = 22.20 \pm 0.18 \times 10 ^ { -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 \sim 3 \% to nearly 20 % during the outburst , while the position angle varied by \sim 120 \degr .
A knot was ejected from the 43 GHz core on 2016 Feb 25 , moving at an apparent speed v _ { \mathrm { app } } = 20.3 c \pm 0.8 c .
From the observed minimum timescale of variability \tau _ { \mathrm { opt } } ^ { \mathrm { min } } \approx 2 hr and derived Doppler factor \delta = 22.6 , we find a size of the emission region r \lesssim 2.6 \times 10 ^ { 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 \sim 0.2 c .