(Svetlana G. Jorstad, Alan P. Marscher, Thomas J. Balonek, Valeri M. Larionov, and Paul S. Smith)
In June 2016 the quasar 3C454.3 underwent a multi-frequency outburst observed at gamma-ray frequencies by the Fermi Large Area Telescope and in the optical R band by several ground-based telescopes. In contrast to previous outbursts, the June 2016 outburst featured a precipitous decay at both gamma-ray and optical frequencies, with the source decreasing in flux density by a factor of 6 over a 24-hour period. The gamma-ray light curve exhibited a three-flare structure observed in previous outbursts. A lower-amplitude outburst was observed in 2016 March, consistent in time with the forward shock of a knot passing through the radio core of the quasar, while the 2016 June outburst is consistent with a reverse shock from the same knot. Intraday variability during several nights was observed at R band throughout the outburst, with flux density changes ranging from 10 to 50 percent over the course of a night. The precipitous optical decay featured quasi-periodic oscillations with an amplitude of 2-3 percent about the mean trend and a characteristic period of 36 minutes. If the quasi-periodic micro-variability is caused by periodic variations of the Doppler factor of emission from a turbulent vortex, we derive a speed of rotation of such vortices of 0.2c. This research was supported in part by NASA Fermi Guest Investigator grant 80NSSC17K0649 and National Science Foundation grant AST-1615796.